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<TITLE>PostgreSQL FAQ</TITLE>
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<H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1>
<P>Last updated: Tue Oct 17 00:21:20 EDT 2000</P>
- <P>Current maintainer: Bruce Momjian (<A href="mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
+ <P>Current maintainer: Bruce Momjian (<A href=
+ "mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR>
</P>
- <P>The most recent version of this document can be viewed at <A href="http://www.Postgresql.org/docs/faq-english.html">http://www.PostgreSQL.org/docs/faq-english.html</A>.</P>
+ <P>The most recent version of this document can be viewed at <A
+ href=
+ "http://www.Postgresql.org/docs/faq-english.html">http://www.PostgreSQL.org/docs/faq-english.html</A>.</P>
- <P>Platform-specific questions are answered at <A href="http://www.PostgreSQL.org/docs/">http://www.PostgreSQL.org/docs/</A>.</P>
+ <P>Platform-specific questions are answered at <A href=
+ "http://www.PostgreSQL.org/docs/">http://www.PostgreSQL.org/docs/</A>.</P>
<HR>
<CENTER>
</CENTER>
<A href="#1.1">1.1</A>) What is PostgreSQL?<BR>
<A href="#1.2">1.2</A>) What's the copyright on PostgreSQL?<BR>
- <A href="#1.3">1.3</A>) What Unix platforms does PostgreSQL run on?<BR>
+ <A href="#1.3">1.3</A>) What Unix platforms does PostgreSQL run
+ on?<BR>
<A href="#1.4">1.4</A>) What non-unix ports are available?<BR>
<A href="#1.5">1.5</A>) Where can I get PostgreSQL?<BR>
<A href="#1.6">1.6</A>) Where can I get support?<BR>
<A href="#1.7">1.7</A>) What is the latest release?<BR>
<A href="#1.8">1.8</A>) What documentation is available?<BR>
- <A href="#1.9">1.9</A>) How do I find out about known bugs or missing features?<BR>
- <A href="#1.10">1.10</A>) How can I learn SQL?<BR>
+ <A href="#1.9">1.9</A>) How do I find out about known bugs or
+ missing features?<BR>
+ <A href="#1.10">1.10</A>) How can I learn <SMALL>SQL</SMALL>?<BR>
<A href="#1.11">1.11</A>) Is PostgreSQL Y2K compliant?<BR>
<A href="#1.12">1.12</A>) How do I join the development team?<BR>
<A href="#1.13">1.13</A>) How do I submit a bug report?<BR>
- <A href="#1.14">1.14</A>) How does PostgreSQL compare to other DBMS's?<BR>
+ <A href="#1.14">1.14</A>) How does PostgreSQL compare to other
+ <SMALL>DBMS</SMALL>'s?<BR>
<CENTER>
<H2>User Client Questions</H2>
</CENTER>
- <A href="#2.1">2.1</A>) Are there ODBC drivers for PostgreSQL?<BR>
- <A href="#2.2">2.2</A>) What tools are available for hooking PostgreSQL to Web pages?<BR>
- <A href="#2.3">2.3</A>) Does PostgreSQL have a graphical user interface? A report generator? An embedded query language interface?<BR>
- <A href="#2.4">2.4</A>) What languages are available to communicate with PostgreSQL?<BR>
+ <A href="#2.1">2.1</A>) Are there <SMALL>ODBC</SMALL> drivers for
+ PostgreSQL?<BR>
+ <A href="#2.2">2.2</A>) What tools are available for hooking
+ PostgreSQL to Web pages?<BR>
+ <A href="#2.3">2.3</A>) Does PostgreSQL have a graphical user
+ interface? A report generator? An embedded query language
+ interface?<BR>
+ <A href="#2.4">2.4</A>) What languages are available to
+ communicate with PostgreSQL?<BR>
<CENTER>
<H2>Administrative Questions</H2>
</CENTER>
- <A href="#3.1">3.1</A>) How do I install PostgreSQL somewhere other than <I>/usr/local/pgsql?</I><BR>
- <A href="#3.2">3.2</A>) When I start the <I>postmaster</I>, I get a <I>Bad System Call</I> or core dumped message. Why?<BR>
- <A href="#3.3">3.3</A>) When I try to start the <I>postmaster</I>, I get <I>IpcMemoryCreate</I> errors. Why?<BR>
- <A href="#3.4">3.4</A>) When I try to start the <I>postmaster</I>, I get <I>IpcSemaphoreCreate</I> errors. Why?<BR>
- <A href="#3.5">3.5</A>) How do I prevent other hosts from accessing my PostgreSQL database?<BR>
- <A href="#3.6">3.6</A>) Why can't I connect to my database from another machine?<BR>
- <A href="#3.7">3.7</A>) All my servers crash under concurrent table access. Why?<BR>
- <A href="#3.8">3.8</A>) How do I tune the database engine for better performance?<BR>
+ <A href="#3.1">3.1</A>) How do I install PostgreSQL somewhere other
+ than <I>/usr/local/pgsql?</I><BR>
+ <A href="#3.2">3.2</A>) When I start the <I>postmaster</I>, I get
+ a <I>Bad System Call</I> or core dumped message. Why?<BR>
+ <A href="#3.3">3.3</A>) When I try to start the <I>postmaster</I>,
+ I get <I>IpcMemoryCreate</I> errors. Why?<BR>
+ <A href="#3.4">3.4</A>) When I try to start the <I>postmaster</I>,
+ I get <I>IpcSemaphoreCreate</I> errors. Why?<BR>
+ <A href="#3.5">3.5</A>) How do I prevent other hosts from
+ accessing my PostgreSQL database?<BR>
+ <A href="#3.6">3.6</A>) Why can't I connect to my database from
+ another machine?<BR>
+ <A href="#3.7">3.7</A>) All my servers crash under concurrent
+ table access. Why?<BR>
+ <A href="#3.8">3.8</A>) How do I tune the database engine for
+ better performance?<BR>
<A href="#3.9">3.9</A>) What debugging features are available?<BR>
- <A href="#3.10">3.10</A>) I get <I>"Sorry, too many clients"</I> when trying to connect. Why?<BR>
- <A href="#3.11">3.11</A>) What are the <I>pg_sorttempNNN.NN</I> files in my database directory?<BR>
+ <A href="#3.10">3.10</A>) I get <I>"Sorry, too many clients"</I>
+ when trying to connect. Why?<BR>
+ <A href="#3.11">3.11</A>) What are the <I>pg_sorttempNNN.NN</I>
+ files in my database directory?<BR>
<CENTER>
<H2>Operational Questions</H2>
</CENTER>
- <A href="#4.1">4.1</A>) Why is the system confused about commas, decimal points, and date formats.<BR>
- <A href="#4.2">4.2</A>) What is the exact difference between binary cursors and normal cursors?<BR>
- <A href="#4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the first few rows of a query?<BR>
- <A href="#4.4">4.4</A>) How do I get a list of tables or other things I can see in <I>psql?</I><BR>
- <A href="#4.5">4.5</A>) How do you remove a column from a table?<BR>
- <A href="#4.6">4.6</A>) What is the maximum size for a row, table, database?<BR>
- <A href="#4.7">4.7</A>) How much database disk space is required to store data from a typical text file?<BR>
- <A href="#4.8">4.8</A>) How do I find out what indices or operations are defined in the database?<BR>
- <A href="#4.9">4.9</A>) My queries are slow or don't make use of the indexes. Why?<BR>
- <A href="#4.10">4.10</A>) How do I see how the query optimizer is evaluating my query?<BR>
+ <A href="#4.1">4.1</A>) Why is the system confused about commas,
+ decimal points, and date formats.<BR>
+ <A href="#4.2">4.2</A>) What is the exact difference between
+ binary cursors and normal cursors?<BR>
+ <A href="#4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the
+ first few rows of a query?<BR>
+ <A href="#4.4">4.4</A>) How do I get a list of tables or other
+ things I can see in <I>psql?</I><BR>
+ <A href="#4.5">4.5</A>) How do you remove a column from a
+ table?<BR>
+ <A href="#4.6">4.6</A>) What is the maximum size for a row, table,
+ database?<BR>
+ <A href="#4.7">4.7</A>) How much database disk space is required
+ to store data from a typical text file?<BR>
+ <A href="#4.8">4.8</A>) How do I find out what indices or
+ operations are defined in the database?<BR>
+ <A href="#4.9">4.9</A>) My queries are slow or don't make use of
+ the indexes. Why?<BR>
+ <A href="#4.10">4.10</A>) How do I see how the query optimizer is
+ evaluating my query?<BR>
<A href="#4.11">4.11</A>) What is an R-tree index?<BR>
<A href="#4.12">4.12</A>) What is Genetic Query Optimization?<BR>
- <A href="#4.13">4.13</A>) How do I do regular expression searches and case-insensitive regular expression searches?<BR>
- <A href="#4.14">4.14</A>) In a query, how do I detect if a field is NULL?<BR>
- <A href="#4.15">4.15</A>) What is the difference between the various character types?<BR>
- <A href="#4.16.1">4.16.1</A>) How do I create a serial/auto-incrementing field?<BR>
- <A href="#4.16.2">4.16.2</A>) How do I get the value of a <SMALL>SERIAL</SMALL> insert?<BR>
- <A href="#4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to a race condition with other users?<BR>
- <A href="#4.17">4.17</A>) What is an <SMALL>OID</SMALL>? What is a <SMALL>TID</SMALL>?<BR>
- <A href="#4.18">4.18</A>) What is the meaning of some of the terms used in PostgreSQL?<BR>
- <A href="#4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc failure: memory exhausted?"</I><BR>
- <A href="#4.20">4.20</A>) How do I tell what PostgreSQL version I am running? <BR>
- <A href="#4.21">4.21</A>) My large-object operations get <I>invalid large obj descriptor.</I> Why?<BR>
- <A href="#4.22">4.22</A>) How do I create a column that will default to the current time?<BR>
- <A href="#4.23">4.23</A>) Why are my subqueries using <CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
+ <A href="#4.13">4.13</A>) How do I do regular expression searches
+ and case-insensitive regular expression searches?<BR>
+ <A href="#4.14">4.14</A>) In a query, how do I detect if a field
+ is <SMALL>NULL</SMALL>?<BR>
+ <A href="#4.15">4.15</A>) What is the difference between the
+ various character types?<BR>
+ <A href="#4.16.1">4.16.1</A>) How do I create a
+ serial/auto-incrementing field?<BR>
+ <A href="#4.16.2">4.16.2</A>) How do I get the value of a
+ <SMALL>SERIAL</SMALL> insert?<BR>
+ <A href="#4.16.3">4.16.3</A>) Don't <I>currval()</I> and
+ <I>nextval()</I> lead to a race condition with other users?<BR>
+ <A href="#4.17">4.17</A>) What is an <SMALL>OID</SMALL>? What is a
+ <SMALL>TID</SMALL>?<BR>
+ <A href="#4.18">4.18</A>) What is the meaning of some of the terms
+ used in PostgreSQL?<BR>
+ <A href="#4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc
+ failure: memory exhausted?"</I><BR>
+ <A href="#4.20">4.20</A>) How do I tell what PostgreSQL version I
+ am running? <BR>
+ <A href="#4.21">4.21</A>) My large-object operations get
+ <I>invalid large obj descriptor.</I> Why?<BR>
+ <A href="#4.22">4.22</A>) How do I create a column that will
+ default to the current time?<BR>
+ <A href="#4.23">4.23</A>) Why are my subqueries using
+ <CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
<A href="#4.24">4.24</A>) How do I do an <I>outer</I> join?<BR>
<CENTER>
<H2>Extending PostgreSQL</H2>
</CENTER>
- <A href="#5.1">5.1</A>) I wrote a user-defined function. When I run it in <I>psql,</I> why does it dump core?<BR>
- <A href="#5.2">5.2</A>) What does the message <I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I> mean?<BR>
- <A href="#5.3">5.3</A>) How can I contribute some nifty new types and functions to PostgreSQL?<BR>
- <A href="#5.4">5.4</A>) How do I write a C function to return a tuple?<BR>
- <A href="#5.5">5.5</A>) I have changed a source file. Why does the recompile not see the change?<BR>
+ <A href="#5.1">5.1</A>) I wrote a user-defined function. When I run
+ it in <I>psql,</I> why does it dump core?<BR>
+ <A href="#5.2">5.2</A>) What does the message
+ <I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I>
+ mean?<BR>
+ <A href="#5.3">5.3</A>) How can I contribute some nifty new types
+ and functions to PostgreSQL?<BR>
+ <A href="#5.4">5.4</A>) How do I write a C function to return a
+ tuple?<BR>
+ <A href="#5.5">5.5</A>) I have changed a source file. Why does the
+ recompile not see the change?<BR>
<HR>
<H4><A name="1.1">1.1</A>) What is PostgreSQL?</H4>
- <P>PostgreSQL is an enhancement of the POSTGRES database management system, a next-generation DBMS research prototype. While PostgreSQL retains the powerful data model and rich data types of POSTGRES, it replaces the PostQuel query language with an extended subset of SQL. PostgreSQL is free and the complete source is available.</P>
-
- <P>PostgreSQL development is performed by a team of Internet developers who all subscribe to the PostgreSQL development mailing list. The current coordinator is Marc G. Fournier (<A href="mailto:scrappy@PostgreSQL.org">scrappy@PostgreSQL.org</A>). (See below on how to join). This team is now responsible for all development of PostgreSQL.</P>
-
- <P>The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many others have contributed to the porting, testing, debugging, and enhancement of the code. The original Postgres code, from which PostgreSQL is derived, was the effort of many graduate students, undergraduate students, and staff programmers working under the direction of Professor Michael Stonebraker at the University of California, Berkeley.</P>
-
- <P>The original name of the software at Berkeley was Postgres. When SQL functionality was added in 1995, its name was changed to Postgres95. The name was changed at the end of 1996 to PostgreSQL.</P>
+ <P>PostgreSQL is an enhancement of the POSTGRES database management
+ system, a next-generation <SMALL>DBMS</SMALL> research prototype.
+ While PostgreSQL retains the powerful data model and rich data
+ types of POSTGRES, it replaces the PostQuel query language with an
+ extended subset of <SMALL>SQL</SMALL>. PostgreSQL is free and the
+ complete source is available.</P>
+
+ <P>PostgreSQL development is performed by a team of Internet
+ developers who all subscribe to the PostgreSQL development mailing
+ list. The current coordinator is Marc G. Fournier (<A href=
+ "mailto:scrappy@PostgreSQL.org">scrappy@PostgreSQL.org</A>). (See
+ below on how to join). This team is now responsible for all
+ development of PostgreSQL.</P>
+
+ <P>The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen.
+ Many others have contributed to the porting, testing, debugging,
+ and enhancement of the code. The original Postgres code, from which
+ PostgreSQL is derived, was the effort of many graduate students,
+ undergraduate students, and staff programmers working under the
+ direction of Professor Michael Stonebraker at the University of
+ California, Berkeley.</P>
+
+ <P>The original name of the software at Berkeley was Postgres. When
+ <SMALL>SQL</SMALL> functionality was added in 1995, its name was
+ changed to Postgres95. The name was changed at the end of 1996 to
+ PostgreSQL.</P>
<P>It is pronounced <I>Post-Gres-Q-L.</I></P>
<P>PostgreSQL Data Base Management System</P>
- <P>Portions copyright (c) 1996-2000, PostgreSQL, Inc Portions Copyright (c) 1994-6 Regents of the University of California</P>
+ <P>Portions copyright (c) 1996-2000, PostgreSQL, Inc Portions
+ Copyright (c) 1994-6 Regents of the University of California</P>
- <P>Permission to use, copy, modify, and distribute this software and its documentation for any purpose, without fee, and without a written agreement is hereby granted, provided that the above copyright notice and this paragraph and the following two paragraphs appear in all copies.</P>
+ <P>Permission to use, copy, modify, and distribute this software
+ and its documentation for any purpose, without fee, and without a
+ written agreement is hereby granted, provided that the above
+ copyright notice and this paragraph and the following two
+ paragraphs appear in all copies.</P>
- <P>IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.</P>
+ <P>IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY
+ PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL
+ DAMAGES, INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS
+ SOFTWARE AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF
+ CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.</P>
- <P>THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.</P>
+ <P>THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY
+ WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE
+ SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS" BASIS, AND THE
+ UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO PROVIDE MAINTENANCE,
+ SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.</P>
- <H4><A name="1.3">1.3</A>) What Unix platforms does PostgreSQL run on?</H4>
+ <H4><A name="1.3">1.3</A>) What Unix platforms does PostgreSQL run
+ on?</H4>
- <P>In general, a modern Unix-compatible platform should be able to run PostgreSQL. The platforms that had received explicit testing at the time of release are listed in the installation instructions.</P>
+ <P>In general, a modern Unix-compatible platform should be able to
+ run PostgreSQL. The platforms that had received explicit testing at
+ the time of release are listed in the installation
+ instructions.</P>
<H4><A name="1.4">1.4</A>) What non-unix ports are available?</H4>
- <P>It is possible to compile the <I>libpq</I> C library, psql, and other interfaces and binaries to run on MS Windows platforms. In this case, the client is running on MS Windows, and communicates via TCP/IP to a server running on one of our supported Unix platforms. A file <I>win31.mak</I> is included in the distribution for making a Win32 <I>libpq</I> library and psql.</P>
+ <H6>Client</H6>
+
+ <P>It is possible to compile the <I>libpq</I> C library, psql, and
+ other interfaces and binaries to run on MS Windows platforms. In
+ this case, the client is running on MS Windows, and communicates
+ via TCP/IP to a server running on one of our supported Unix
+ platforms. A file <I>win31.mak</I> is included in the distribution
+ for making a Win32 <I>libpq</I> library and psql. PostgreSQL also
+ communicates with <SMALL>ODBC</SMALL> clients.</P>
- <P>The database server can run on Windows NT and later using Cygwin, the Cygnus Unix/NT porting library. See <I>pgsql/doc/FAQ_MSWIN</I> in the distribution. The database server does not run on MS Windows 9X because Cygwin does not support the required features on those platforms. We have no plans to do a native port to any Microsoft platform.</P>
+ <H6>Server</H6>
+
+ <P>The database server can run on Windows NT and later using
+ Cygwin, the Cygnus Unix/NT porting library. See
+ <I>pgsql/doc/FAQ_MSWIN</I> in the distribution or the MS Windows
+ FAQ on our web site. The database server does not run on MS Windows
+ 9X because Cygwin does not support the required features on those
+ platforms. We have no plan to do a native port to any Microsoft
+ platform.</P>
<H4><A name="1.5">1.5</A>) Where can I get PostgreSQL?</H4>
- <P>The primary anonymous ftp site for PostgreSQL is <A href="ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A>. For mirror sites, see our main Web site.</P>
+ <P>The primary anonymous ftp site for PostgreSQL is <A href=
+ "ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A>.
+ For mirror sites, see our main Web site.</P>
<H4><A name="1.6">1.6</A>) Where can I get support?</H4>
- <P>There is no support for PostgreSQL from the University of California, Berkeley. It is maintained through volunteer effort.</P>
+ <P>There is no support for PostgreSQL from the University of
+ California, Berkeley. It is maintained through volunteer
+ effort.</P>
- <P>The main mailing list is: <A href="mailto:pgsql-general@PostgreSQL.org">pgsql-general@PostgreSQL.org</A>. It is available for discussion of matters pertaining to PostgreSQL. To subscribe, send mail with the following lines in the body (not the subject line)</P>
+ <P>The main mailing list is: <A href=
+ "mailto:pgsql-general@PostgreSQL.org">pgsql-general@PostgreSQL.org</A>.
+ It is available for discussion of matters pertaining to PostgreSQL.
+ To subscribe, send mail with the following lines in the body (not
+ the subject line)</P>
<PRE>
subscribe
end
</PRE>
- <P>to <A href="mailto:pgsql-general-request@PostgreSQL.org">pgsql-general-request@PostgreSQL.org</A>.</P>
+ <P>to <A href=
+ "mailto:pgsql-general-request@PostgreSQL.org">pgsql-general-request@PostgreSQL.org</A>.</P>
- <P>There is also a digest list available. To subscribe to this list, send email to: <A href="mailto:pgsql-general-digest-request@PostgreSQL.org">pgsql-general-digest-request@PostgreSQL.org</A> with a body of:</P>
+ <P>There is also a digest list available. To subscribe to this
+ list, send email to: <A href=
+ "mailto:pgsql-general-digest-request@PostgreSQL.org">pgsql-general-digest-request@PostgreSQL.org</A>
+ with a body of:</P>
<PRE>
subscribe
end
</PRE>
- Digests are sent out to members of this list whenever the main list has received around 30k of messages.
+ Digests are sent out to members of this list whenever the main list
+ has received around 30k of messages.
- <P>The bugs mailing list is available. To subscribe to this list, send email to <A href="mailto:pgsql-bugs-request@PostgreSQL.org">pgsql-bugs-request@PostgreSQL.org</A> with a body of:</P>
+ <P>The bugs mailing list is available. To subscribe to this list,
+ send email to <A href=
+ "mailto:pgsql-bugs-request@PostgreSQL.org">pgsql-bugs-request@PostgreSQL.org</A>
+ with a body of:</P>
<PRE>
subscribe
end
</PRE>
- There is also a developers discussion mailing list available. To subscribe to this list, send email to <A href="mailto:pgsql-hackers-request@PostgreSQL.org">pgsql-hackers-request@PostgreSQL.org</A> with a body of:
+ There is also a developers discussion mailing list available. To
+ subscribe to this list, send email to <A href=
+ "mailto:pgsql-hackers-request@PostgreSQL.org">pgsql-hackers-request@PostgreSQL.org</A>
+ with a body of:
<PRE>
subscribe
end
</PRE>
- <P>Additional mailing lists and information about PostgreSQL can be found via the PostgreSQL WWW home page at:</P>
+ <P>Additional mailing lists and information about PostgreSQL can be
+ found via the PostgreSQL WWW home page at:</P>
<BLOCKQUOTE>
<A href="http://www.PostgreSQL.org">http://www.PostgreSQL.org</A>
</BLOCKQUOTE>
- <P>There is also an IRC channel on EFNet, channel <I>#PostgreSQL.</I> I use the unix command <CODE>irc -c '#PostgreSQL' "$USER" irc.phoenix.net.</CODE></P>
+ <P>There is also an IRC channel on EFNet, channel
+ <I>#PostgreSQL.</I> I use the unix command <CODE>irc -c
+ '#PostgreSQL' "$USER" irc.phoenix.net.</CODE></P>
- <P>A list of commercial PostgreSQL support is available at <A href="http://www.postgresql.org/users-lounge/commercial-support.html">http://www.postgresql.org/users-lounge/commercial-support.html</A>.</P>
+ <P>A list of commercial PostgreSQL support is available at <A href=
+ "http://www.postgresql.org/users-lounge/commercial-support.html">http://www.postgresql.org/users-lounge/commercial-support.html</A>.</P>
<H4><A name="1.7">1.7</A>) What is the latest release?</H4>
<H4><A name="1.8">1.8</A>) What documentation is available?</H4>
- <P>Several manuals, manual pages, and some small test examples are included in the distribution. See the <I>/doc</I> directory. You can also browse the manual online at <A href="http://www.PostgreSQL.org/docs/postgres">http://www.PostgreSQL.org/docs/postgres</A>.</P>
+ <P>Several manuals, manual pages, and some small test examples are
+ included in the distribution. See the <I>/doc</I> directory. You
+ can also browse the manual online at <A href=
+ "http://www.PostgreSQL.org/docs/postgres">http://www.PostgreSQL.org/docs/postgres</A>.</P>
- <P>There is a PostgreSQL book available at <A href="http://www.PostgreSQL.org/docs/awbook.html">http://www.PostgreSQL.org/docs/awbook.html</A>.</P>
+ <P>There is a PostgreSQL book available at <A href=
+ "http://www.PostgreSQL.org/docs/awbook.html">http://www.PostgreSQL.org/docs/awbook.html</A>.</P>
- <P><I>psql</I> has some nice \d commands to show information about types, operators, functions, aggregates, etc.</P>
+ <P><I>psql</I> has some nice \d commands to show information about
+ types, operators, functions, aggregates, etc.</P>
<P>Our Web site contains even more documentation.</P>
- <H4><A name="1.9">1.9</A>) How do I find out about known bugs or missing features?</H4>
+ <H4><A name="1.9">1.9</A>) How do I find out about known bugs or
+ missing features?</H4>
- <P>PostgreSQL supports an extended subset of SQL-92. See our <A href="http://www.PostgreSQL.org/docs/todo.html">TODO</A> list for known bugs, missing features, and future plans.</P>
+ <P>PostgreSQL supports an extended subset of <SMALL>SQL</SMALL>-92.
+ See our <A href="http://www.PostgreSQL.org/docs/todo.html">TODO</A>
+ list for known bugs, missing features, and future plans.</P>
- <H4><A name="1.10">1.10</A>) How can I learn SQL?</H4>
+ <H4><A name="1.10">1.10</A>) How can I learn
+ <SMALL>SQL</SMALL>?</H4>
- <P>The PostgreSQL book at <A href="http://www.PostgreSQL.org/docs/awbook.html">http://www.PostgreSQL.org/docs/awbook.html</A> teaches SQL. There is a nice tutorial at <A href="http://w3.one.net/~jhoffman/sqltut.htm">http://w3.one.net/~jhoffman/sqltut.htm</A> and at <A href="http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM">http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM.</A></P>
+ <P>The PostgreSQL book at <A href=
+ "http://www.PostgreSQL.org/docs/awbook.html">http://www.PostgreSQL.org/docs/awbook.html</A>
+ teaches <SMALL>SQL</SMALL>. There is a nice tutorial at <A href=
+ "http://w3.one.net/~jhoffman/sqltut.htm">http://w3.one.net/~jhoffman/sqltut.htm</A>
+ and at <A href=
+ "http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM">
+ http://ourworld.compuserve.com/homepages/graeme_birchall/HTM_COOK.HTM.</A></P>
- <P>Another one is "Teach Yourself SQL in 21 Days, Second Edition" at <A href="http://members.tripod.com/er4ebus/sql/index.htm">http://members.tripod.com/er4ebus/sql/index.htm</A></P>
+ <P>Another one is "Teach Yourself SQL in 21 Days, Second Edition"
+ at <A href=
+ "http://members.tripod.com/er4ebus/sql/index.htm">http://members.tripod.com/er4ebus/sql/index.htm</A></P>
- <P>Many of our users like <I>The Practical SQL Handbook</I>, Bowman, Judith S., et al., Addison-Wesley. Others like <I>The Complete Reference SQL</I>, Groff et al., McGraw-Hill.</P>
+ <P>Many of our users like <I>The Practical SQL Handbook</I>,
+ Bowman, Judith S., et al., Addison-Wesley. Others like <I>The
+ Complete Reference SQL</I>, Groff et al., McGraw-Hill.</P>
<H4><A name="1.11">1.11</A>) Is PostgreSQL Y2K compliant?</H4>
- <P>Yes, we easily handle dates past the year 2000AD, and before 2000BC.</P>
+ <P>Yes, we easily handle dates past the year 2000AD, and before
+ 2000BC.</P>
- <H4><A name="1.12">1.12</A>) How do I join the development team?</H4>
+ <H4><A name="1.12">1.12</A>) How do I join the development
+ team?</H4>
- <P>First, download the latest source and read the PostgreSQL Developers documentation on our Web site, or in the distribution. Second, subscribe to the <I>pgsql-hackers</I> and <I>pgsql-patches</I> mailing lists. Third, submit high-quality patches to pgsql-patches.</P>
+ <P>First, download the latest source and read the PostgreSQL
+ Developers documentation on our Web site, or in the distribution.
+ Second, subscribe to the <I>pgsql-hackers</I> and
+ <I>pgsql-patches</I> mailing lists. Third, submit high-quality
+ patches to pgsql-patches.</P>
- <P>There are about a dozen people who have commit privileges to the PostgreSQL CVS archive. They each have submitted so many high-quality patches that it was impossible for the existing committers to keep up, and we had confidence that patches they committed were of high quality.</P>
+ <P>There are about a dozen people who have commit privileges to the
+ PostgreSQL <SMALL>CVS</SMALL> archive. They each have submitted so
+ many high-quality patches that it was impossible for the existing
+ committers to keep up, and we had confidence that patches they
+ committed were of high quality.</P>
<H4><A name="1.13">1.13</A>) How do I submit a bug report?</H4>
- <P>Fill out the "bug-template" file and send it to: <A href="mailto:pgsql-bugs@PostgreSQL.org">pgsql-bugs@PostgreSQL.org</A></P>
+ <P>Fill out the "bug-template" file and send it to: <A href=
+ "mailto:pgsql-bugs@PostgreSQL.org">pgsql-bugs@PostgreSQL.org</A></P>
- <P>Also check out our ftp site <A href="ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A> to see if there is a more recent PostgreSQL version or patches.</P>
+ <P>Also check out our ftp site <A href=
+ "ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A> to
+ see if there is a more recent PostgreSQL version or patches.</P>
- <H4><A name="1.14">1.14</A>) How does PostgreSQL compare to other DBMS's?</H4>
+ <H4><A name="1.14">1.14</A>) How does PostgreSQL compare to other
+ <SMALL>DBMS</SMALL>'s?</H4>
- <P>There are several ways of measuring software: features, performance, reliability, support, and price.</P>
+ <P>There are several ways of measuring software: features,
+ performance, reliability, support, and price.</P>
<DL>
<DT><B>Features</B></DT>
- <DD>PostgreSQL has most features present in large commercial DBMS's, like transactions, subselects, triggers, views, foreign key referential integrity, and sophisticated locking. We have some features they don't have, like user-defined types, inheritance, rules, and multi-version concurrency control to reduce lock contention. We don't have outer joins, but are working on them.<BR>
+ <DD>PostgreSQL has most features present in large commercial
+ <SMALL>DBMS</SMALL>'s, like transactions, subselects, triggers,
+ views, foreign key referential integrity, and sophisticated
+ locking. We have some features they don't have, like user-defined
+ types, inheritance, rules, and multi-version concurrency control
+ to reduce lock contention.<BR>
<BR>
</DD>
<DT><B>Performance</B></DT>
- <DD>PostgreSQL runs in two modes. Normal <I>fsync</I> mode flushes every completed transaction to disk, guaranteeing that if the OS crashes or loses power in the next few seconds, all your data is safely stored on disk. In this mode, we are slower than most commercial databases, partly because few of them do such conservative flushing to disk in their default modes. In <I>no-fsync</I> mode, we are usually faster than commercial databases, though in this mode, an OS crash could cause data corruption. We are working to provide an intermediate mode that suffers less performance overhead than full fsync mode, and will allow data integrity within 30 seconds of an OS crash.<BR>
+ <DD>PostgreSQL runs in two modes. Normal <I>fsync</I> mode
+ flushes every completed transaction to disk, guaranteeing that if
+ the OS crashes or loses power in the next few seconds, all your
+ data is safely stored on disk. In this mode, we are slower than
+ most commercial databases, partly because few of them do such
+ conservative flushing to disk in their default modes. In
+ <I>no-fsync</I> mode, we are usually faster than commercial
+ databases, though in this mode, an OS crash could cause data
+ corruption. We are working to provide an intermediate mode that
+ suffers less performance overhead than full fsync mode, and will
+ allow data integrity within 30 seconds of an OS crash.<BR>
<BR>
- In comparison to MySQL or leaner database systems, we are slower on inserts/updates because we have transaction overhead. Of course, MySQL doesn't have any of the features mentioned in the <I>Features</I> section above. We are built for flexibility and features, though we continue to improve performance through profiling and source code analysis. There is an interesting Web page comparing PostgreSQL to MySQL at <A href="http://openacs.org/why-not-mysql.html">http://openacs.org/why-not-mysql.html</A><BR>
+ In comparison to MySQL or leaner database systems, we are slower
+ on inserts/updates because we have transaction overhead. Of
+ course, MySQL doesn't have any of the features mentioned in the
+ <I>Features</I> section above. We are built for flexibility and
+ features, though we continue to improve performance through
+ profiling and source code analysis. There is an interesting Web
+ page comparing PostgreSQL to MySQL at <A href=
+ "http://openacs.org/why-not-mysql.html">http://openacs.org/why-not-mysql.html</A><BR>
+
<BR>
- We handle each user connection by creating a Unix process. Backend processes share data buffers and locking information. With multiple CPU's, multiple backends can easily run on different CPU's.<BR>
+ We handle each user connection by creating a Unix process.
+ Backend processes share data buffers and locking information.
+ With multiple CPU's, multiple backends can easily run on
+ different CPU's.<BR>
<BR>
</DD>
<DT><B>Reliability</B></DT>
- <DD>We realize that a DBMS must be reliable, or it is worthless. We strive to release well-tested, stable code that has a minimum of bugs. Each release has at least one month of beta testing, and our release history shows that we can provide stable, solid releases that are ready for production use. We believe we compare favorably to other database software in this area.<BR>
+ <DD>We realize that a <SMALL>DBMS</SMALL> must be reliable, or it
+ is worthless. We strive to release well-tested, stable code that
+ has a minimum of bugs. Each release has at least one month of
+ beta testing, and our release history shows that we can provide
+ stable, solid releases that are ready for production use. We
+ believe we compare favorably to other database software in this
+ area.<BR>
<BR>
</DD>
<DT><B>Support</B></DT>
- <DD>Our mailing list provides a large group of developers and users to help resolve any problems encountered. While we can not guarantee a fix, commercial DBMS's don't always supply a fix either. Direct access to developers, the user community, manuals, and the source code often make PostgreSQL support superior to other DBMS's. There is commercial per-incident support available for those who need it. (See support FAQ item.)<BR>
+ <DD>Our mailing list provides a large group of developers and
+ users to help resolve any problems encountered. While we can not
+ guarantee a fix, commercial <SMALL>DBMS</SMALL>'s don't always
+ supply a fix either. Direct access to developers, the user
+ community, manuals, and the source code often make PostgreSQL
+ support superior to other <SMALL>DBMS</SMALL>'s. There is
+ commercial per-incident support available for those who need it.
+ (See support FAQ item.)<BR>
<BR>
</DD>
<DT><B>Price</B></DT>
- <DD>We are free for all use, both commercial and non-commercial. You can add our code to your product with no limitations, except those outlined in our BSD-style license stated above.<BR>
+ <DD>We are free for all use, both commercial and non-commercial.
+ You can add our code to your product with no limitations, except
+ those outlined in our BSD-style license stated above.<BR>
<BR>
</DD>
</DL>
<H2>User Client Questions</H2>
</CENTER>
- <H4><A name="2.1">2.1</A>) Are there ODBC drivers for PostgreSQL?</H4>
+ <H4><A name="2.1">2.1</A>) Are there <SMALL>ODBC</SMALL> drivers
+ for PostgreSQL?</H4>
- <P>There are two ODBC drivers available, PsqlODBC and OpenLink ODBC.</P>
+ <P>There are two <SMALL>ODBC</SMALL> drivers available, PsqlODBC
+ and OpenLink <SMALL>ODBC</SMALL>.</P>
- <P>PsqlODBC is included in the distribution. More information about it can be gotten from <A href="ftp://ftp.PostgreSQL.org/pub/odbc/">ftp://ftp.PostgreSQL.org/pub/odbc/</A>.</P>
+ <P>PsqlODBC is included in the distribution. More information about
+ it can be gotten from <A href=
+ "ftp://ftp.PostgreSQL.org/pub/odbc/">ftp://ftp.PostgreSQL.org/pub/odbc/</A>.</P>
- <P>OpenLink ODBC can be gotten from <A href="http://www.openlinksw.com/">http://www.openlinksw.com</A>. It works with their standard ODBC client software so you'll have PostgreSQL ODBC available on every client platform they support (Win, Mac, Unix, VMS).</P>
+ <P>OpenLink <SMALL>ODBC</SMALL> can be gotten from <A href=
+ "http://www.openlinksw.com/">http://www.openlinksw.com</A>. It
+ works with their standard <SMALL>ODBC</SMALL> client software so
+ you'll have PostgreSQL <SMALL>ODBC</SMALL> available on every
+ client platform they support (Win, Mac, Unix, VMS).</P>
- <P>They will probably be selling this product to people who need commercial-quality support, but a freeware version will always be available. Questions to <A href="mailto:postgres95@openlink.co.uk">postgres95@openlink.co.uk</A>.</P>
+ <P>They will probably be selling this product to people who need
+ commercial-quality support, but a freeware version will always be
+ available. Questions to <A href=
+ "mailto:postgres95@openlink.co.uk">postgres95@openlink.co.uk</A>.</P>
- <P>See also the <A href="http://www.PostgreSQL.org/docs/programmer/odbc.htm">ODBC chapter of the Programmer's Guide</A>.</P>
+ <P>See also the <A href=
+ "http://www.PostgreSQL.org/docs/programmer/odbc.htm">ODBC chapter
+ of the Programmer's Guide</A>.</P>
- <H4><A name="2.2">2.2</A>) What tools are available for hooking PostgreSQL to Web pages?</H4>
+ <H4><A name="2.2">2.2</A>) What tools are available for hooking
+ PostgreSQL to Web pages?</H4>
- <P>A nice introduction to Database-backed Web pages can be seen at: <A href="http://www.webtools.com">http://www.webtools.com</A></P>
+ <P>A nice introduction to Database-backed Web pages can be seen at:
+ <A href="http://www.webtools.com">http://www.webtools.com</A></P>
- <P>There is also one at <A href="http://www.phone.net/home/mwm/hotlist/">http://www.phone.net/home/mwm/hotlist/.</A></P>
+ <P>There is also one at <A href=
+ "http://www.phone.net/home/mwm/hotlist/">http://www.phone.net/home/mwm/hotlist/.</A></P>
- <P>For Web integration, PHP is an excellent interface. It is at <A href="http://www.php.net">http://www.php.net</A></P>
+ <P>For Web integration, PHP is an excellent interface. It is at <A
+ href="http://www.php.net">http://www.php.net</A></P>
<P>For complex cases, many use the Perl interface and CGI.pm.</P>
- <P>A WWW gateway based on WDB using Perl can be downloaded from <A href="http://www.eol.ists.ca/~dunlop/wdb-p95">http://www.eol.ists.ca/~dunlop/wdb-p95</A></P>
+ <P>A WWW gateway based on WDB using Perl can be downloaded from <A
+ href=
+ "http://www.eol.ists.ca/~dunlop/wdb-p95">http://www.eol.ists.ca/~dunlop/wdb-p95</A></P>
- <H4><A name="2.3">2.3</A>) Does PostgreSQL have a graphical user interface? A report generator? An embedded query language interface?</H4>
+ <H4><A name="2.3">2.3</A>) Does PostgreSQL have a graphical user
+ interface? A report generator? An embedded query language
+ interface?</H4>
- <P>We have a nice graphical user interface called <I>pgaccess,</I> which is shipped as part of the distribution. <I>Pgaccess</I> also has a report generator. The Web page is <A href="http://www.flex.ro/pgaccess">http://www.flex.ro/pgaccess</A></P>
+ <P>We have a nice graphical user interface called <I>pgaccess,</I>
+ which is shipped as part of the distribution. <I>Pgaccess</I> also
+ has a report generator. The Web page is <A href=
+ "http://www.flex.ro/pgaccess">http://www.flex.ro/pgaccess</A></P>
- <P>We also include <I>ecpg,</I> which is an embedded SQL query language interface for C.</P>
+ <P>We also include <I>ecpg,</I> which is an embedded SQL query
+ language interface for C.</P>
- <H4><A name="2.4">2.4</A>) What languages are available to communicate with PostgreSQL?</H4>
+ <H4><A name="2.4">2.4</A>) What languages are available to
+ communicate with PostgreSQL?</H4>
<P>We have:</P>
<LI>C Easy API (libpgeasy)</LI>
- <LI>Embedded HTML (<A href="http://www.php.net">PHP from http://www.php.net</A>)</LI>
+ <LI>Embedded <SMALL>HTML</SMALL> (<A href=
+ "http://www.php.net">PHP from http://www.php.net</A>)</LI>
</UL>
<HR>
<H2>Administrative Questions</H2>
</CENTER>
- <H4><A name="3.1">3.1</A>) How do I install PostgreSQL somewhere other than <I>/usr/local/pgsql?</I></H4>
-
- <P>Specify the <I>--prefix</I> option when running <I>configure.</I></P>
-
- <H4><A name="3.2">3.2</A>) When I start the <I>postmaster</I>, I get a <I>Bad System Call</I> or core dumped message. Why?</H4>
-
- <P>It could be a variety of problems, but first check to see that you have System V extensions installed in your kernel. PostgreSQL requires kernel support for shared memory and semaphores.</P>
-
- <H4><A name="3.3">3.3</A>) When I try to start the <I>postmaster,</I> I get <I>IpcMemoryCreate</I> errors. Why?</H4>
-
- <P>You either do not have shared memory configured properly in your kernel or you need to enlarge the shared memory available in the kernel. The exact amount you need depends on your architecture and how many buffers and backend processes you configure for the <I>postmaster.</I> For most systems, with default numbers of buffers and processes, you need a minimum of ~1MB.</P>
-
- <H4><A name="3.4">3.4</A>) When I try to start the <I>postmaster,</I> I get <I>IpcSemaphoreCreate</I> errors. Why?</H4>
-
- <P>If the error message is <I>IpcSemaphoreCreate: semget failed (No space left on device)</I> then your kernel is not configured with enough semaphores. Postgres needs one semaphore per potential backend process. A temporary solution is to start the <I>postmaster</I> with a smaller limit on the number of backend processes. Use <I>-N</I> with a parameter less than the default of 32. A more permanent solution is to increase your kernel's <SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI</SMALL> parameters.</P>
-
- <P>If the error message is something else, you might not have semaphore support configured in your kernel at all.</P>
-
- <H4><A name="3.5">3.5</A>) How do I prevent other hosts from accessing my PostgreSQL database?</H4>
-
- <P>By default, PostgreSQL only allows connections from the local machine using Unix domain sockets. Other machines will not be able to connect unless you add the <I>-i</I> flag to the <I>postmaster,</I> <B>and</B> enable host-based authentication by modifying the file <I>$PGDATA/pg_hba.conf</I> accordingly. This will allow TCP/IP connections.</P>
-
- <H4><A name="3.6">3.6</A>) Why can't I connect to my database from another machine?</H4>
-
- <P>The default configuration allows only unix domain socket connections from the local machine. To enable TCP/IP connections, make sure the <I>postmaster</I> has been started with the <I>-i</I> option, and add an appropriate host entry to the file <I>pgsql/data/pg_hba.conf</I>.</P>
-
- <H4><A name="3.7">3.7</A>) All my servers crash under concurrent table access. Why?</H4>
-
- <P>This problem can be caused by a kernel that is not configured to support semaphores.</P>
-
- <H4><A name="3.8">3.8</A>) How do I tune the database engine for better performance?</H4>
-
- <P>Certainly, indices can speed up queries. The <SMALL>EXPLAIN</SMALL> command allows you to see how PostgreSQL is interpreting your query, and which indices are being used.</P>
-
- <P>If you are doing a lot of <SMALL>INSERTs</SMALL>, consider doing them in a large batch using the <SMALL>COPY</SMALL> command. This is much faster than individual <SMALL>INSERTS.</SMALL> Second, statements not in a <SMALL>BEGIN WORK/COMMIT</SMALL> transaction block are considered to be in their own transaction. Consider performing several statements in a single transaction block. This reduces the transaction overhead. Also consider dropping and recreating indices when making large data changes.</P>
-
- <P>There are several tuning options. You can disable <I>fsync()</I> by starting the <I>postmaster</I> with a <I>-o -F</I> option. This will prevent <I>fsync()'s</I> from flushing to disk after every transaction.</P>
-
- <P>You can also use the <I>postmaster</I> <I>-B</I> option to increase the number of shared memory buffers used by the backend processes. If you make this parameter too high, the <I>postmaster</I> may not start because you've exceeded your kernel's limit on shared memory space. Each buffer is 8K and the default is 64 buffers.</P>
-
- <P>You can also use the backend <I>-S</I> option to increase the maximum amount of memory used by the backend process for temporary sorts. The <I>-S</I> value is measured in kilobytes, and the default is 512 (ie, 512K).</P>
-
- <P>You can also use the <SMALL>CLUSTER</SMALL> command to group data in tables to match an index. See the <SMALL>CLUSTER</SMALL> manual page for more details.</P>
-
- <H4><A name="3.9">3.9</A>) What debugging features are available?</H4>
-
- <P>PostgreSQL has several features that report status information that can be valuable for debugging purposes.</P>
-
- <P>First, by running <I>configure</I> with the --enable-cassert option, many <I>assert()'s</I> monitor the progress of the backend and halt the program when something unexpected occurs.</P>
-
- <P>Both <I>postmaster</I> and <I>postgres</I> have several debug options available. First, whenever you start the <I>postmaster,</I> make sure you send the standard output and error to a log file, like:</P>
+ <H4><A name="3.1">3.1</A>) How do I install PostgreSQL somewhere
+ other than <I>/usr/local/pgsql?</I></H4>
+
+ <P>Specify the <I>--prefix</I> option when running
+ <I>configure.</I></P>
+
+ <H4><A name="3.2">3.2</A>) When I start the <I>postmaster</I>, I
+ get a <I>Bad System Call</I> or core dumped message. Why?</H4>
+
+ <P>It could be a variety of problems, but first check to see that
+ you have System V extensions installed in your kernel. PostgreSQL
+ requires kernel support for shared memory and semaphores.</P>
+
+ <H4><A name="3.3">3.3</A>) When I try to start the
+ <I>postmaster,</I> I get <I>IpcMemoryCreate</I> errors. Why?</H4>
+
+ <P>You either do not have shared memory configured properly in your
+ kernel or you need to enlarge the shared memory available in the
+ kernel. The exact amount you need depends on your architecture and
+ how many buffers and backend processes you configure for the
+ <I>postmaster.</I> For most systems, with default numbers of
+ buffers and processes, you need a minimum of ~1MB.</P>
+
+ <H4><A name="3.4">3.4</A>) When I try to start the
+ <I>postmaster,</I> I get <I>IpcSemaphoreCreate</I> errors.
+ Why?</H4>
+
+ <P>If the error message is <I>IpcSemaphoreCreate: semget failed (No
+ space left on device)</I> then your kernel is not configured with
+ enough semaphores. Postgres needs one semaphore per potential
+ backend process. A temporary solution is to start the
+ <I>postmaster</I> with a smaller limit on the number of backend
+ processes. Use <I>-N</I> with a parameter less than the default of
+ 32. A more permanent solution is to increase your kernel's
+ <SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI</SMALL> parameters.</P>
+
+ <P>If the error message is something else, you might not have
+ semaphore support configured in your kernel at all.</P>
+
+ <H4><A name="3.5">3.5</A>) How do I prevent other hosts from
+ accessing my PostgreSQL database?</H4>
+
+ <P>By default, PostgreSQL only allows connections from the local
+ machine using Unix domain sockets. Other machines will not be able
+ to connect unless you add the <I>-i</I> flag to the
+ <I>postmaster,</I> <B>and</B> enable host-based authentication by
+ modifying the file <I>$PGDATA/pg_hba.conf</I> accordingly. This
+ will allow TCP/IP connections.</P>
+
+ <H4><A name="3.6">3.6</A>) Why can't I connect to my database from
+ another machine?</H4>
+
+ <P>The default configuration allows only unix domain socket
+ connections from the local machine. To enable TCP/IP connections,
+ make sure the <I>postmaster</I> has been started with the <I>-i</I>
+ option, and add an appropriate host entry to the file
+ <I>pgsql/data/pg_hba.conf</I>.</P>
+
+ <H4><A name="3.7">3.7</A>) All my servers crash under concurrent
+ table access. Why?</H4>
+
+ <P>This problem can be caused by a kernel that is not configured to
+ support semaphores.</P>
+
+ <H4><A name="3.8">3.8</A>) How do I tune the database engine for
+ better performance?</H4>
+
+ <P>Certainly, indices can speed up queries. The
+ <SMALL>EXPLAIN</SMALL> command allows you to see how PostgreSQL is
+ interpreting your query, and which indices are being used.</P>
+
+ <P>If you are doing a lot of <SMALL>INSERTs</SMALL>, consider doing
+ them in a large batch using the <SMALL>COPY</SMALL> command. This
+ is much faster than individual <SMALL>INSERTS.</SMALL> Second,
+ statements not in a <SMALL>BEGIN WORK/COMMIT</SMALL> transaction
+ block are considered to be in their own transaction. Consider
+ performing several statements in a single transaction block. This
+ reduces the transaction overhead. Also consider dropping and
+ recreating indices when making large data changes.</P>
+
+ <P>There are several tuning options. You can disable <I>fsync()</I>
+ by starting the <I>postmaster</I> with a <I>-o -F</I> option. This
+ will prevent <I>fsync()'s</I> from flushing to disk after every
+ transaction.</P>
+
+ <P>You can also use the <I>postmaster</I> <I>-B</I> option to
+ increase the number of shared memory buffers used by the backend
+ processes. If you make this parameter too high, the
+ <I>postmaster</I> may not start because you've exceeded your
+ kernel's limit on shared memory space. Each buffer is 8K and the
+ default is 64 buffers.</P>
+
+ <P>You can also use the backend <I>-S</I> option to increase the
+ maximum amount of memory used by the backend process for temporary
+ sorts. The <I>-S</I> value is measured in kilobytes, and the
+ default is 512 (ie, 512K).</P>
+
+ <P>You can also use the <SMALL>CLUSTER</SMALL> command to group
+ data in tables to match an index. See the <SMALL>CLUSTER</SMALL>
+ manual page for more details.</P>
+
+ <H4><A name="3.9">3.9</A>) What debugging features are
+ available?</H4>
+
+ <P>PostgreSQL has several features that report status information
+ that can be valuable for debugging purposes.</P>
+
+ <P>First, by running <I>configure</I> with the --enable-cassert
+ option, many <I>assert()'s</I> monitor the progress of the backend
+ and halt the program when something unexpected occurs.</P>
+
+ <P>Both <I>postmaster</I> and <I>postgres</I> have several debug
+ options available. First, whenever you start the <I>postmaster,</I>
+ make sure you send the standard output and error to a log file,
+ like:</P>
<PRE>
cd /usr/local/pgsql
./bin/postmaster >server.log 2>&1 &
</PRE>
- <P>This will put a server.log file in the top-level PostgreSQL directory. This file contains useful information about problems or errors encountered by the server. <I>Postmaster</I> has a <I>-d</I> option that allows even more detailed information to be reported. The <I>-d</I> option takes a number that specifies the debug level. Be warned that high debug level values generate large log files.</P>
-
- <P>If the <I>postmaster</I> is not running, you can actually run the <I>postgres</I> backend from the command line, and type your SQL statement directly. This is recommended <B>only</B> for debugging purposes. Note that a newline terminates the query, not a semicolon. If you have compiled with debugging symbols, you can use a debugger to see what is happening. Because the backend was not started from the <I>postmaster,</I> it is not running in an identical environment and locking/backend interaction problems may not be duplicated.</P>
-
- <P>If the <I>postmaster</I> is running, start <I>psql</I> in one window, then find the <SMALL>PID</SMALL> of the <I>postgres</I> process used by <I>psql.</I> Use a debugger to attach to the <I>postgres</I> <SMALL>PID.</SMALL> You can set breakpoints in the debugger and issue queries from <I>psql.</I> If you are debugging <I>postgres</I> startup, you can set PGOPTIONS="-W n", then start <I>psql.</I> This will cause startup to delay for <I>n</I> seconds so you can attach with the debugger and trace through the startup sequence.</P>
-
- <P>The <I>postgres</I> program has <I>-s, -A,</I> and <I>-t</I> options that can be very useful for debugging and performance measurements.</P>
-
- <P>You can also compile with profiling to see what functions are taking execution time. The backend profile files will be deposited in the <I>pgsql/data/base/dbname</I> directory. The client profile file will be put in the client's current directory.</P>
-
- <H4><A name="3.10">3.10</A>) I get 'Sorry, too many clients' when trying to connect. Why?</H4>
-
- <P>You need to increase the <I>postmaster's</I> limit on how many concurrent backend processes it can start.</P>
-
- <P>In PostgreSQL 6.5 and up, the default limit is 32 processes. You can increase it by restarting the <I>postmaster</I> with a suitable <I>-N</I> value. With the default configuration you can set <I>-N</I> as large as 1024. If you need more, increase <SMALL>MAXBACKENDS</SMALL> in <I>include/config.h</I> and rebuild. You can set the default value of <I>-N</I> at configuration time, if you like, using <I>configure's</I> <I>--with-maxbackends</I> switch.</P>
-
- <P>Note that if you make <I>-N</I> larger than 32, you must also increase <I>-B</I> beyond its default of 64; <I>-B</I> must be at least twice <I>-N,</I> and probably should be more than that for best performance. For large numbers of backend processes, you are also likely to find that you need to increase various Unix kernel configuration parameters. Things to check include the maximum size of shared memory blocks, <SMALL>SHMMAX;</SMALL> the maximum number of semaphores, <SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI;</SMALL> the maximum number of processes, <SMALL>NPROC;</SMALL> the maximum number of processes per user, <SMALL>MAXUPRC;</SMALL> and the maximum number of open files, <SMALL>NFILE</SMALL> and <SMALL>NINODE.</SMALL> The reason that PostgreSQL has a limit on the number of allowed backend processes is so your system won't run out of resources.</P>
-
- <P>In PostgreSQL versions prior to 6.5, the maximum number of backends was 64, and changing it required a rebuild after altering the MaxBackendId constant in <I>include/storage/sinvaladt.h.</I></P>
-
- <H4><A name="3.11">3.11</A>) What are the <I>pg_sorttempNNN.NN</I> files in my database directory?</H4>
-
- <P>They are temporary files generated by the query executor. For example, if a sort needs to be done to satisfy an <SMALL>ORDER BY,</SMALL> and the sort requires more space than the backend's <I>-S</I> parameter allows, then temporary files are created to hold the extra data.</P>
-
- <P>The temporary files should be deleted automatically, but might not if a backend crashes during a sort. If you have no backends running at the time, it is safe to delete the pg_tempNNN.NN files.</P>
+ <P>This will put a server.log file in the top-level PostgreSQL
+ directory. This file contains useful information about problems or
+ errors encountered by the server. <I>Postmaster</I> has a <I>-d</I>
+ option that allows even more detailed information to be reported.
+ The <I>-d</I> option takes a number that specifies the debug level.
+ Be warned that high debug level values generate large log
+ files.</P>
+
+ <P>If the <I>postmaster</I> is not running, you can actually run
+ the <I>postgres</I> backend from the command line, and type your
+ <SMALL>SQL</SMALL> statement directly. This is recommended
+ <B>only</B> for debugging purposes. Note that a newline terminates
+ the query, not a semicolon. If you have compiled with debugging
+ symbols, you can use a debugger to see what is happening. Because
+ the backend was not started from the <I>postmaster,</I> it is not
+ running in an identical environment and locking/backend interaction
+ problems may not be duplicated.</P>
+
+ <P>If the <I>postmaster</I> is running, start <I>psql</I> in one
+ window, then find the <SMALL>PID</SMALL> of the <I>postgres</I>
+ process used by <I>psql.</I> Use a debugger to attach to the
+ <I>postgres</I> <SMALL>PID.</SMALL> You can set breakpoints in the
+ debugger and issue queries from <I>psql.</I> If you are debugging
+ <I>postgres</I> startup, you can set PGOPTIONS="-W n", then start
+ <I>psql.</I> This will cause startup to delay for <I>n</I> seconds
+ so you can attach with the debugger and trace through the startup
+ sequence.</P>
+
+ <P>The <I>postgres</I> program has <I>-s, -A,</I> and <I>-t</I>
+ options that can be very useful for debugging and performance
+ measurements.</P>
+
+ <P>You can also compile with profiling to see what functions are
+ taking execution time. The backend profile files will be deposited
+ in the <I>pgsql/data/base/dbname</I> directory. The client profile
+ file will be put in the client's current directory.</P>
+
+ <H4><A name="3.10">3.10</A>) I get 'Sorry, too many clients' when
+ trying to connect. Why?</H4>
+
+ <P>You need to increase the <I>postmaster's</I> limit on how many
+ concurrent backend processes it can start.</P>
+
+ <P>In PostgreSQL 6.5 and up, the default limit is 32 processes. You
+ can increase it by restarting the <I>postmaster</I> with a suitable
+ <I>-N</I> value. With the default configuration you can set
+ <I>-N</I> as large as 1024. If you need more, increase
+ <SMALL>MAXBACKENDS</SMALL> in <I>include/config.h</I> and rebuild.
+ You can set the default value of <I>-N</I> at configuration time,
+ if you like, using <I>configure's</I> <I>--with-maxbackends</I>
+ switch.</P>
+
+ <P>Note that if you make <I>-N</I> larger than 32, you must also
+ increase <I>-B</I> beyond its default of 64; <I>-B</I> must be at
+ least twice <I>-N,</I> and probably should be more than that for
+ best performance. For large numbers of backend processes, you are
+ also likely to find that you need to increase various Unix kernel
+ configuration parameters. Things to check include the maximum size
+ of shared memory blocks, <SMALL>SHMMAX;</SMALL> the maximum number
+ of semaphores, <SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI;</SMALL> the
+ maximum number of processes, <SMALL>NPROC;</SMALL> the maximum
+ number of processes per user, <SMALL>MAXUPRC;</SMALL> and the
+ maximum number of open files, <SMALL>NFILE</SMALL> and
+ <SMALL>NINODE.</SMALL> The reason that PostgreSQL has a limit on
+ the number of allowed backend processes is so your system won't run
+ out of resources.</P>
+
+ <P>In PostgreSQL versions prior to 6.5, the maximum number of
+ backends was 64, and changing it required a rebuild after altering
+ the MaxBackendId constant in
+ <I>include/storage/sinvaladt.h.</I></P>
+
+ <H4><A name="3.11">3.11</A>) What are the <I>pg_sorttempNNN.NN</I>
+ files in my database directory?</H4>
+
+ <P>They are temporary files generated by the query executor. For
+ example, if a sort needs to be done to satisfy an <SMALL>ORDER
+ BY,</SMALL> and the sort requires more space than the backend's
+ <I>-S</I> parameter allows, then temporary files are created to
+ hold the extra data.</P>
+
+ <P>The temporary files should be deleted automatically, but might
+ not if a backend crashes during a sort. If you have no backends
+ running at the time, it is safe to delete the pg_tempNNN.NN
+ files.</P>
<HR>
<CENTER>
<H2>Operational Questions</H2>
</CENTER>
- <H4><A name="4.1">4.1</A>) Why is system confused about commas, decimal points, and date formats.</H4>
+ <H4><A name="4.1">4.1</A>) Why is system confused about commas,
+ decimal points, and date formats.</H4>
- <P>Check your locale configuration. PostgreSQL uses the locale setting of the user that ran the <I>postmaster</I> process. There are postgres and psql SET commands to control the date format. Set those accordingly for your operating environment.</P>
+ <P>Check your locale configuration. PostgreSQL uses the locale
+ setting of the user that ran the <I>postmaster</I> process. There
+ are postgres and psql <SMALL>SET</SMALL> commands to control the
+ date format. Set those accordingly for your operating
+ environment.</P>
- <H4><A name="4.2">4.2</A>) What is the exact difference between binary cursors and normal cursors?</H4>
+ <H4><A name="4.2">4.2</A>) What is the exact difference between
+ binary cursors and normal cursors?</H4>
- <P>See the <SMALL>DECLARE</SMALL> manual page for a description.</P>
+ <P>See the <SMALL>DECLARE</SMALL> manual page for a
+ description.</P>
- <H4><A name="4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the first few rows of a query?</H4>
+ <H4><A name="4.3">4.3</A>) How do I <SMALL>SELECT</SMALL> only the
+ first few rows of a query?</H4>
- <P>See the <SMALL>FETCH</SMALL> manual page, or use SELECT ... LIMIT....</P>
+ <P>See the <SMALL>FETCH</SMALL> manual page, or use
+ <SMALL>SELECT</SMALL> ... <SMALL>LIMIT</SMALL>....</P>
- <P>The entire query may have to be evaluated, even if you only want the first few rows. Consider a query that has an <SMALL>ORDER BY.</SMALL> If there is an index that matches the <SMALL>ORDER BY</SMALL>, PostgreSQL may be able to evaluate only the first few records requested, or the entire query may have to be evaluated until the desired rows have been generated.</P>
+ <P>The entire query may have to be evaluated, even if you only want
+ the first few rows. Consider a query that has an <SMALL>ORDER
+ BY.</SMALL> If there is an index that matches the <SMALL>ORDER
+ BY</SMALL>, PostgreSQL may be able to evaluate only the first few
+ records requested, or the entire query may have to be evaluated
+ until the desired rows have been generated.</P>
- <H4><A name="4.4">4.4</A>) How do I get a list of tables or other things I can see in <I>psql?</I><BR>
+ <H4><A name="4.4">4.4</A>) How do I get a list of tables or other
+ things I can see in <I>psql?</I><BR>
</H4>
- <P>You can read the source code for <I>psql</I> in file <I>pgsql/src/bin/psql/describe.c.</I> It contains SQL commands that generate the output for psql's backslash commands. You can also start <I>psql</I> with the <I>-E</I> option so it will print out the queries it uses to execute the commands you give.</P>
+ <P>You can read the source code for <I>psql</I> in file
+ <I>pgsql/src/bin/psql/describe.c.</I> It contains
+ <SMALL>SQL</SMALL> commands that generate the output for psql's
+ backslash commands. You can also start <I>psql</I> with the
+ <I>-E</I> option so it will print out the queries it uses to
+ execute the commands you give.</P>
- <H4><A name="4.5">4.5</A>) How do you remove a column from a table?</H4>
+ <H4><A name="4.5">4.5</A>) How do you remove a column from a
+ table?</H4>
- <P>We do not support <SMALL>ALTER TABLE DROP COLUMN,</SMALL> but do this:</P>
+ <P>We do not support <SMALL>ALTER TABLE DROP COLUMN,</SMALL> but do
+ this:</P>
<PRE>
SELECT ... -- select all columns but the one you want to remove
INTO TABLE new_table
ALTER TABLE new_table RENAME TO old_table;
</PRE>
- <H4><A name="4.6">4.6</A>) What is the maximum size for a row, table, database?</H4>
+ <H4><A name="4.6">4.6</A>) What is the maximum size for a row,
+ table, database?</H4>
<P>These are the limits:</P>
<PRE>
Maximum number of columns in a table? unlimited
Maximum number of indexes on a table? unlimited
</PRE>
- Of course, these are not actually unlimited, but limited to available disk space.
+ Of course, these are not actually unlimited, but limited to
+ available disk space.
- <H4><A name="4.7">4.7</A>) How much database disk space is required to store data from a typical text file?<BR>
+ <H4><A name="4.7">4.7</A>) How much database disk space is required
+ to store data from a typical text file?<BR>
</H4>
- <P>A PostgreSQL database may need six-and-a-half times the disk space required to store the data in a flat file.</P>
+ <P>A PostgreSQL database may need six-and-a-half times the disk
+ space required to store the data in a flat file.</P>
- <P>Consider a file of 300,000 lines with two integers on each line. The flat file is 2.4MB. The size of the PostgreSQL database file containing this data can be estimated at 14MB:</P>
+ <P>Consider a file of 300,000 lines with two integers on each line.
+ The flat file is 2.4MB. The size of the PostgreSQL database file
+ containing this data can be estimated at 14MB:</P>
<PRE>
36 bytes: each row header (approximate)
+ 8 bytes: two int fields @ 4 bytes each
1755 database pages * 8192 bytes per page = 14,376,960 bytes (14MB)
</PRE>
- <P>Indexes do not require as much overhead, but do contain the data that is being indexed, so they can be large also.</P>
+ <P>Indexes do not require as much overhead, but do contain the data
+ that is being indexed, so they can be large also.</P>
- <H4><A name="4.8">4.8</A>) How do I find out what indices or operations are defined in the database?</H4>
+ <H4><A name="4.8">4.8</A>) How do I find out what indices or
+ operations are defined in the database?</H4>
- <P><I>psql</I> has a variety of backslash commands to show such information. Use \? to see them.</P>
+ <P><I>psql</I> has a variety of backslash commands to show such
+ information. Use \? to see them.</P>
- <P>Also try the file <I>pgsql/src/tutorial/syscat.source.</I> It illustrates many of the <SMALL>SELECT</SMALL>s needed to get information from the database system tables.</P>
+ <P>Also try the file <I>pgsql/src/tutorial/syscat.source.</I> It
+ illustrates many of the <SMALL>SELECT</SMALL>s needed to get
+ information from the database system tables.</P>
- <H4><A name="4.9">4.9</A>) My queries are slow or don't make use of the indexes. Why?</H4>
+ <H4><A name="4.9">4.9</A>) My queries are slow or don't make use of
+ the indexes. Why?</H4>
- <P>PostgreSQL does not automatically maintain statistics. V<SMALL>ACUUM</SMALL> must be run to update the statistics. After statistics are updated, the optimizer knows how many rows in the table, and can better decide if it should use indices. Note that the optimizer does not use indices in cases when the table is small because a sequential scan would be faster.</P>
+ <P>PostgreSQL does not automatically maintain statistics.
+ V<SMALL>ACUUM</SMALL> must be run to update the statistics. After
+ statistics are updated, the optimizer knows how many rows in the
+ table, and can better decide if it should use indices. Note that
+ the optimizer does not use indices in cases when the table is small
+ because a sequential scan would be faster.</P>
- <P>For column-specific optimization statistics, use <SMALL>VACUUM ANALYZE.</SMALL> <SMALL>VACUUM ANALYZE</SMALL> is important for complex multijoin queries, so the optimizer can estimate the number of rows returned from each table, and choose the proper join order. The backend does not keep track of column statistics on its own, so <SMALL>VACUUM ANALYZE</SMALL> must be run to collect them periodically.</P>
+ <P>For column-specific optimization statistics, use <SMALL>VACUUM
+ ANALYZE.</SMALL> <SMALL>VACUUM ANALYZE</SMALL> is important for
+ complex multijoin queries, so the optimizer can estimate the number
+ of rows returned from each table, and choose the proper join order.
+ The backend does not keep track of column statistics on its own, so
+ <SMALL>VACUUM ANALYZE</SMALL> must be run to collect them
+ periodically.</P>
- <P>Indexes are usually not used for <SMALL>ORDER BY</SMALL> operations: a sequential scan followed by an explicit sort is faster than an indexscan of all tuples of a large table, because it takes fewer disk accesses.</P>
+ <P>Indexes are usually not used for <SMALL>ORDER BY</SMALL>
+ operations: a sequential scan followed by an explicit sort is
+ faster than an indexscan of all tuples of a large table, because it
+ takes fewer disk accesses.</P>
- <P>When using wild-card operators such as <SMALL>LIKE</SMALL> or <I>~,</I> indices can only be used if the beginning of the search is anchored to the start of the string. So, to use indices, <SMALL>LIKE</SMALL> searches should not begin with <I>%,</I> and <I>~</I>(regular expression searches) should start with <I>^.</I></P>
+ <P>When using wild-card operators such as <SMALL>LIKE</SMALL> or
+ <I>~,</I> indices can only be used if the beginning of the search
+ is anchored to the start of the string. So, to use indices,
+ <SMALL>LIKE</SMALL> searches should not begin with <I>%,</I> and
+ <I>~</I>(regular expression searches) should start with
+ <I>^.</I></P>
- <H4><A name="4.10">4.10</A>) How do I see how the query optimizer is evaluating my query?</H4>
+ <H4><A name="4.10">4.10</A>) How do I see how the query optimizer
+ is evaluating my query?</H4>
<P>See the <SMALL>EXPLAIN</SMALL> manual page.</P>
<H4><A name="4.11">4.11</A>) What is an R-tree index?</H4>
- <P>An R-tree index is used for indexing spatial data. A hash index can't handle range searches. A B-tree index only handles range searches in a single dimension. R-tree's can handle multi-dimensional data. For example, if an R-tree index can be built on an attribute of type <I>point,</I> the system can more efficiently answer queries such as "select all points within a bounding rectangle."</P>
-
- <P>The canonical paper that describes the original R-tree design is:</P>
-
- <P>Guttman, A. "R-trees: A Dynamic Index Structure for Spatial Searching." Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57.</P>
-
- <P>You can also find this paper in Stonebraker's "Readings in Database Systems".</P>
-
- <P>Built-in R-trees can handle polygons and boxes. In theory, R-trees can be extended to handle higher number of dimensions. In practice, extending R-trees requires a bit of work and we don't currently have any documentation on how to do it.</P>
-
- <H4><A name="4.12">4.12</A>) What is Genetic Query Optimization?</H4>
-
- <P>The GEQO module speeds query optimization when joining many tables by means of a Genetic Algorithm (GA). It allows the handling of large join queries through nonexhaustive search.</P>
-
- <H4><A name="4.13">4.13</A>) How do I do regular expression searches and case-insensitive regular expression searches?</H4>
-
- <P>The <I>~</I> operator does regular expression matching, and <I>~*</I> does case-insensitive regular expression matching. There is no case-insensitive variant of the LIKE operator, but you can get the effect of case-insensitive <SMALL>LIKE</SMALL> with this:</P>
+ <P>An R-tree index is used for indexing spatial data. A hash index
+ can't handle range searches. A B-tree index only handles range
+ searches in a single dimension. R-tree's can handle
+ multi-dimensional data. For example, if an R-tree index can be
+ built on an attribute of type <I>point,</I> the system can more
+ efficiently answer queries such as "select all points within a
+ bounding rectangle."</P>
+
+ <P>The canonical paper that describes the original R-tree design
+ is:</P>
+
+ <P>Guttman, A. "R-trees: A Dynamic Index Structure for Spatial
+ Searching." Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data,
+ 45-57.</P>
+
+ <P>You can also find this paper in Stonebraker's "Readings in
+ Database Systems".</P>
+
+ <P>Built-in R-trees can handle polygons and boxes. In theory,
+ R-trees can be extended to handle higher number of dimensions. In
+ practice, extending R-trees requires a bit of work and we don't
+ currently have any documentation on how to do it.</P>
+
+ <H4><A name="4.12">4.12</A>) What is Genetic Query
+ Optimization?</H4>
+
+ <P>The <SMALL>GEQO</SMALL> module speeds query optimization when
+ joining many tables by means of a Genetic Algorithm (GA). It allows
+ the handling of large join queries through nonexhaustive
+ search.</P>
+
+ <H4><A name="4.13">4.13</A>) How do I do regular expression
+ searches and case-insensitive regular expression searches?</H4>
+
+ <P>The <I>~</I> operator does regular expression matching, and
+ <I>~*</I> does case-insensitive regular expression matching. There
+ is no case-insensitive variant of the <SMALL>LIKE</SMALL> operator,
+ but you can get the effect of case-insensitive <SMALL>LIKE</SMALL>
+ with this:</P>
<PRE>
WHERE lower(textfield) LIKE lower(pattern)
</PRE>
- <H4><A name="4.14">4.14</A>) In a query, how do I detect if a field is NULL?</H4>
+ <H4><A name="4.14">4.14</A>) In a query, how do I detect if a field
+ is <SMALL>NULL</SMALL>?</H4>
- <P>You test the column with IS NULL and IS NOT NULL.</P>
+ <P>You test the column with <SMALL>IS NULL</SMALL>IS NOT NULL.</P>
- <H4><A name="4.15">4.15</A>) What is the difference between the various character types?</H4>
+ <H4><A name="4.15">4.15</A>) What is the difference between the
+ various character types?</H4>
<PRE>
Type Internal Name Notes
--------------------------------------------------
BYTEA bytea variable-length byte array (null-safe)
</PRE>
- <P>You will see the internal name when examining system catalogs and in some error messages.</P>
+ <P>You will see the internal name when examining system catalogs
+ and in some error messages.</P>
- <P>The last four types above are "varlena" types (i.e., the first four bytes on disk are the length, followed by the data). Thus the actual space used is slightly greater than the declared size. However, these data types are also subject to compression or being stored out-of-line by TOAST, so the space on disk might also be less than expected.</P>
+ <P>The last four types above are "varlena" types (i.e., the first
+ four bytes on disk are the length, followed by the data). Thus the
+ actual space used is slightly greater than the declared size.
+ However, these data types are also subject to compression or being
+ stored out-of-line by <SMALL>TOAST</SMALL>, so the space on disk
+ might also be less than expected.</P>
- <H4><A name="4.16.1">4.16.1</A>) How do I create a serial/auto-incrementing field?</H4>
+ <H4><A name="4.16.1">4.16.1</A>) How do I create a
+ serial/auto-incrementing field?</H4>
- <P>PostgreSQL supports a <SMALL>SERIAL</SMALL> data type. It auto-creates a sequence and index on the column. For example, this:</P>
+ <P>PostgreSQL supports a <SMALL>SERIAL</SMALL> data type. It
+ auto-creates a sequence and index on the column. For example,
+ this:</P>
<PRE>
CREATE TABLE person (
id SERIAL,
);
CREATE UNIQUE INDEX person_id_key ON person ( id );
</PRE>
- See the <I>create_sequence</I> manual page for more information about sequences. You can also use each row's <I>OID</I> field as a unique value. However, if you need to dump and reload the database, you need to use <I>pg_dump's -o</I> option or <SMALL>COPY WITH OIDS</SMALL> option to preserve the <SMALL>OID</SMALL>s.
-
- <P><A href="http://www.PostgreSQL.org/docs/aw_pgsql_book">Numbering Rows.</A></P>
-
- <H4><A name="4.16.2">4.16.2</A>) How do I get the value of a <SMALL>SERIAL</SMALL> insert?</H4>
-
- <P>One approach is to to retrieve the next SERIAL value from the sequence object with the <I>nextval()</I> function <I>before</I> inserting and then insert it explicitly. Using the example table in <A href="#4.16.1">4.16.1</A>, that might look like this:</P>
+ See the <I>create_sequence</I> manual page for more information
+ about sequences. You can also use each row's <I>OID</I> field as a
+ unique value. However, if you need to dump and reload the database,
+ you need to use <I>pg_dump's -o</I> option or <SMALL>COPY WITH
+ OIDS</SMALL> option to preserve the <SMALL>OID</SMALL>s.
+
+ <P><A href="http://www.PostgreSQL.org/docs/aw_pgsql_book">Numbering
+ Rows.</A></P>
+
+ <H4><A name="4.16.2">4.16.2</A>) How do I get the value of a
+ <SMALL>SERIAL</SMALL> insert?</H4>
+
+ <P>One approach is to to retrieve the next <SMALL>SERIAL</SMALL>
+ value from the sequence object with the <I>nextval()</I> function
+ <I>before</I> inserting and then insert it explicitly. Using the
+ example table in <A href="#4.16.1">4.16.1</A>, that might look like
+ this:</P>
<PRE>
$newSerialID = nextval('person_id_seq');
INSERT INTO person (id, name) VALUES ($newSerialID, 'Blaise Pascal');
</PRE>
- You would then also have the new value stored in <CODE>$newSerialID</CODE> for use in other queries (e.g., as a foreign key to the <CODE>person</CODE> table). Note that the name of the automatically created SEQUENCE object will be named <<I>table</I>>_<<I>serialcolumn</I>>_<I>seq</I>, where <I>table</I> and <I>serialcolumn</I> are the names of your table and your SERIAL column, respectively.
-
- <P>Alternatively, you could retrieve the assigned SERIAL value with the <I>currval</I>() function <I>after</I> it was inserted by default, e.g.,</P>
+ You would then also have the new value stored in
+ <CODE>$newSerialID</CODE> for use in other queries (e.g., as a
+ foreign key to the <CODE>person</CODE> table). Note that the name
+ of the automatically created <SMALL>SEQUENCE</SMALL> object will be
+ named <<I>table</I>>_<<I>serialcolumn</I>>_<I>seq</I>,
+ where <I>table</I> and <I>serialcolumn</I> are the names of your
+ table and your <SMALL>SERIAL</SMALL> column, respectively.
+
+ <P>Alternatively, you could retrieve the assigned
+ <SMALL>SERIAL</SMALL> value with the <I>currval</I>() function
+ <I>after</I> it was inserted by default, e.g.,</P>
<PRE>
INSERT INTO person (name) VALUES ('Blaise Pascal');
$newID = currval('person_id_seq');
</PRE>
- Finally, you could use the <A href="#4.17"><SMALL>OID</SMALL></A> returned from the INSERT statement to look up the default value, though this is probably the least portable approach. In Perl, using DBI with Edmund Mergl's DBD::Pg module, the oid value is made available via <I>$sth->{pg_oid_status} after $sth->execute().</I>
+ Finally, you could use the <A href="#4.17"><SMALL>OID</SMALL></A>
+ returned from the <SMALL>INSERT</SMALL> statement to look up the
+ default value, though this is probably the least portable approach.
+ In Perl, using DBI with Edmund Mergl's DBD::Pg module, the oid
+ value is made available via <I>$sth->{pg_oid_status} after
+ $sth->execute().</I>
- <H4><A name="4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to a race condition with other users?</H4>
+ <H4><A name="4.16.3">4.16.3</A>) Don't <I>currval()</I> and
+ <I>nextval()</I> lead to a race condition with other users?</H4>
<P>No. This is handled by the backends.</P>
- <H4><A name="4.17">4.17</A>) What is an <SMALL>OID</SMALL>? What is a <SMALL>TID</SMALL>?</H4>
-
- <P><SMALL>OID</SMALL>s are PostgreSQL's answer to unique row ids. Every row that is created in PostgreSQL gets a unique <SMALL>OID</SMALL>. All <SMALL>OID</SMALL>s generated during <I>initdb</I> are less than 16384 (from <I>backend/access/transam.h</I>). All user-created <SMALL>OID</SMALL>s are equal to or greater than this. By default, all these <SMALL>OID</SMALL>s are unique not only within a table or database, but unique within the entire PostgreSQL installation.</P>
-
- <P>PostgreSQL uses <SMALL>OID</SMALL>s in its internal system tables to link rows between tables. These <SMALL>OID</SMALL>s can be used to identify specific user rows and used in joins. It is recommended you use column type <SMALL>OID</SMALL> to store <SMALL>OID</SMALL> values. You can create an index on the <SMALL>OID</SMALL> field for faster access.</P>
-
- <P>O<SMALL>id</SMALL>s are assigned to all new rows from a central area that is used by all databases. If you want to change the <SMALL>OID</SMALL> to something else, or if you want to make a copy of the table, with the original <SMALL>OID</SMALL>'s, there is no reason you can't do it:</P>
+ <H4><A name="4.17">4.17</A>) What is an <SMALL>OID</SMALL>? What is
+ a <SMALL>TID</SMALL>?</H4>
+
+ <P><SMALL>OID</SMALL>s are PostgreSQL's answer to unique row ids.
+ Every row that is created in PostgreSQL gets a unique
+ <SMALL>OID</SMALL>. All <SMALL>OID</SMALL>s generated during
+ <I>initdb</I> are less than 16384 (from
+ <I>backend/access/transam.h</I>). All user-created
+ <SMALL>OID</SMALL>s are equal to or greater than this. By default,
+ all these <SMALL>OID</SMALL>s are unique not only within a table or
+ database, but unique within the entire PostgreSQL installation.</P>
+
+ <P>PostgreSQL uses <SMALL>OID</SMALL>s in its internal system
+ tables to link rows between tables. These <SMALL>OID</SMALL>s can
+ be used to identify specific user rows and used in joins. It is
+ recommended you use column type <SMALL>OID</SMALL> to store
+ <SMALL>OID</SMALL> values. You can create an index on the
+ <SMALL>OID</SMALL> field for faster access.</P>
+
+ <P>O<SMALL>id</SMALL>s are assigned to all new rows from a central
+ area that is used by all databases. If you want to change the
+ <SMALL>OID</SMALL> to something else, or if you want to make a copy
+ of the table, with the original <SMALL>OID</SMALL>'s, there is no
+ reason you can't do it:</P>
<PRE>
CREATE TABLE new_table(old_oid oid, mycol int);
SELECT old_oid, mycol INTO new FROM old;
-->
</PRE>
- <P>O<SMALL>ID</SMALL>s are stored as 4-byte integers, and will overflow at 4 billion. No one has reported this ever happening, and we plan to have the limit removed before anyone does.</P>
+ <P>O<SMALL>ID</SMALL>s are stored as 4-byte integers, and will
+ overflow at 4 billion. No one has reported this ever happening, and
+ we plan to have the limit removed before anyone does.</P>
- <P>T<SMALL>ID</SMALL>s are used to identify specific physical rows with block and offset values. Tids change after rows are modified or reloaded. They are used by index entries to point to physical rows.</P>
+ <P>T<SMALL>ID</SMALL>s are used to identify specific physical rows
+ with block and offset values. Tids change after rows are modified
+ or reloaded. They are used by index entries to point to physical
+ rows.</P>
- <H4><A name="4.18">4.18</A>) What is the meaning of some of the terms used in PostgreSQL?</H4>
+ <H4><A name="4.18">4.18</A>) What is the meaning of some of the
+ terms used in PostgreSQL?</H4>
- <P>Some of the source code and older documentation use terms that have more common usage. Here are some:</P>
+ <P>Some of the source code and older documentation use terms that
+ have more common usage. Here are some:</P>
<UL>
<LI>table, relation, class</LI>
<LI>range variable, table name, table alias</LI>
</UL>
- <P>A list of general database terms can be found at: <A href="http://www.comptechnews.com/~reaster/dbdesign.html">http://www.comptechnews.com/~reaster/dbdesign.html</A></P>
+ <P>A list of general database terms can be found at: <A href=
+ "http://www.comptechnews.com/~reaster/dbdesign.html">http://www.comptechnews.com/~reaster/dbdesign.html</A></P>
- <H4><A name="4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc failure: memory exhausted?"</I><BR>
+ <H4><A name="4.19">4.19</A>) Why do I get the error <I>"FATAL:
+ palloc failure: memory exhausted?"</I><BR>
</H4>
- <P>It is possible you have run out of virtual memory on your system, or your kernel has a low limit for certain resources. Try this before starting the <I>postmaster:</I></P>
+ <P>It is possible you have run out of virtual memory on your
+ system, or your kernel has a low limit for certain resources. Try
+ this before starting the <I>postmaster:</I></P>
<PRE>
ulimit -d 65536
limit datasize 64m
</PRE>
- Depending on your shell, only one of these may succeed, but it will set your process data segment limit much higher and perhaps allow the query to complete. This command applies to the current process, and all subprocesses created after the command is run. If you are having a problem with the SQL client because the backend is returning too much data, try it before starting the client.
-
- <H4><A name="4.20">4.20</A>) How do I tell what PostgreSQL version I am running?<BR>
+ Depending on your shell, only one of these may succeed, but it will
+ set your process data segment limit much higher and perhaps allow
+ the query to complete. This command applies to the current process,
+ and all subprocessesHTML & CSS specifications are available from http://www.w3.org/
+To learn more about Tidy see http://www.w3.org/People/Raggett/tidy/
+Please send bug reports to Dave Raggett care of <html-tidy@w3.org>
+Lobby your company to join W3C, see http://www.w3.org/Consortium
+ created after the command is run. If you are
+ having a problem with the <SMALL>SQL</SMALL> client because the
+ backend is returning too much data, try it before starting the
+ client.
+
+ <H4><A name="4.20">4.20</A>) How do I tell what PostgreSQL version
+ I am running?<BR>
</H4>
<P>From <I>psql,</I> type <CODE>select version();</CODE></P>
- <H4><A name="4.21">4.21</A>) My large-object operations get <I>invalid large obj descriptor.</I> Why?<BR>
+ <H4><A name="4.21">4.21</A>) My large-object operations get
+ <I>invalid large obj descriptor.</I> Why?<BR>
</H4>
- <P>You need to put <CODE>BEGIN WORK</CODE> and <CODE>COMMIT</CODE> around any use of a large object handle, that is, surrounding <CODE>lo_open</CODE> ... <CODE>lo_close.</CODE></P>
+ <P>You need to put <CODE>BEGIN WORK</CODE> and <CODE>COMMIT</CODE>
+ around any use of a large object handle, that is, surrounding
+ <CODE>lo_open</CODE> ... <CODE>lo_close.</CODE></P>
- <P>Currently PostgreSQL enforces the rule by closing large object handles at transaction commit. So the first attempt to do anything with the handle will draw <I>invalid large obj descriptor.</I> So code that used to work (at least most of the time) will now generate that error message if you fail to use a transaction.</P>
+ <P>Currently PostgreSQL enforces the rule by closing large object
+ handles at transaction commit. So the first attempt to do anything
+ with the handle will draw <I>invalid large obj descriptor.</I> So
+ code that used to work (at least most of the time) will now
+ generate that error message if you fail to use a transaction.</P>
- <P>If you are using a client interface like ODBC you may need to set <CODE>auto-commit off.</CODE></P>
+ <P>If you are using a client interface like <SMALL>ODBC</SMALL> you
+ may need to set <CODE>auto-commit off.</CODE></P>
- <H4><A name="4.22">4.22</A>) How do I create a column that will default to the current time?<BR>
+ <H4><A name="4.22">4.22</A>) How do I create a column that will
+ default to the current time?<BR>
</H4>
<P>Use <I>now()</I>:</P>
</CODE>
</PRE>
- <H4><A name="4.23">4.23</A>) Why are my subqueries using <CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
+ <H4><A name="4.23">4.23</A>) Why are my subqueries using
+ <CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
</H4>
- <P>Currently, we join subqueries to outer queries by sequentially scanning the result of the subquery for each row of the outer query. A workaround is to replace <CODE>IN</CODE> with <CODE>EXISTS</CODE>:</P>
+ <P>Currently, we join subqueries to outer queries by sequentially
+ scanning the result of the subquery for each row of the outer
+ query. A workaround is to replace <CODE>IN</CODE> with
+ <CODE>EXISTS</CODE>:</P>
<PRE>
<CODE>SELECT *
FROM tab
<H4><A name="4.24">4.24</A>) How do I do an <I>outer</I> join?<BR>
</H4>
- <P>PostgreSQL 7.1 and later supports outer joins. In previous releases, outer joins can be simulated using <SMALL>UNION</SMALL> and <SMALL>NOT IN</SMALL>. For example, when joining <I>tab1</I> and <I>tab2,</I> the following query does an <I>outer</I> join of the two tables:</P>
+ <P>PostgreSQL 7.1 and later supports outer joins. Here is an
+ example:</P>
+<PRE>
+ SELECT *
+ FROM t1 LEFT OUTER JOIN t2 USING (col);
+</PRE>
+ This will join t1.col to t2.col, and return any unjoined rows in t1
+ with <SMALL>NULL</SMALL> values for t2 columns. A
+ <SMALL>RIGHT</SMALL> join would return unjoined rows of table t2. A
+ <SMALL>FULL</SMALL> join would return unjoined rows from t1 and t2.
+ The word <SMALL>OUTER</SMALL> is optional and is assumed in
+ <SMALL>LEFT</SMALL>, <SMALL>RIGHT</SMALL>, and <SMALL>FULL</SMALL>
+ joins. Ordinary joins are called <SMALL>INNER</SMALL> joins.<BR>
+ <BR>
+ In previous releases, outer joins can be simulated using
+ <SMALL>UNION</SMALL> and <SMALL>NOT IN</SMALL>. For example, when
+ joining <I>tab1</I> and <I>tab2,</I> the following query does an
+ <I>outer</I> join of the two tables:<BR>
+ <BR>
+
<PRE>
SELECT tab1.col1, tab2.col2
FROM tab1, tab2
<H2>Extending PostgreSQL</H2>
</CENTER>
- <H4><A name="5.1">5.1</A>) I wrote a user-defined function. When I run it in <I>psql,</I> why does it dump core?</H4>
+ <H4><A name="5.1">5.1</A>) I wrote a user-defined function. When I
+ run it in <I>psql,</I> why does it dump core?</H4>
- <P>The problem could be a number of things. Try testing your user-defined function in a stand-alone test program first.</P>
+ <P>The problem could be a number of things. Try testing your
+ user-defined function in a stand-alone test program first.</P>
- <H4><A name="5.2">5.2</A>) What does the message <I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I> mean?</H4>
+ <H4><A name="5.2">5.2</A>) What does the message
+ <I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I>
+ mean?</H4>
- <P>You are <I>pfree'</I>ing something that was not <I>palloc'</I>ed. Beware of mixing <I>malloc/free</I> and <I>palloc/pfree.</I></P>
+ <P>You are <I>pfree'</I>ing something that was not
+ <I>palloc'</I>ed. Beware of mixing <I>malloc/free</I> and
+ <I>palloc/pfree.</I></P>
- <H4><A name="5.3">5.3</A>) How can I contribute some nifty new types and functions to PostgreSQL?</H4>
+ <H4><A name="5.3">5.3</A>) How can I contribute some nifty new
+ types and functions to PostgreSQL?</H4>
- <P>Send your extensions to the <I>pgsql-hackers</I> mailing list, and they will eventually end up in the <I>contrib/</I> subdirectory.</P>
+ <P>Send your extensions to the <I>pgsql-hackers</I> mailing list,
+ and they will eventually end up in the <I>contrib/</I>
+ subdirectory.</P>
- <H4><A name="5.4">5.4</A>) How do I write a C function to return a tuple?</H4>
+ <H4><A name="5.4">5.4</A>) How do I write a C function to return a
+ tuple?</H4>
- <P>This requires wizardry so extreme that the authors have never tried it, though in principle it can be done.</P>
+ <P>This requires wizardry so extreme that the authors have never
+ tried it, though in principle it can be done.</P>
- <H4><A name="5.5">5.5</A>) I have changed a source file. Why does the recompile not see the change?</H4>
+ <H4><A name="5.5">5.5</A>) I have changed a source file. Why does
+ the recompile not see the change?</H4>
- <P>The <I>Makefiles</I> do not have the proper dependencies for include files. You have to do a <I>make clean</I> and then another <I>make</I>. If you are using GCC you can use the <I>--enable-depend</I> option of <I>configure</I> to have the compiler compute the dependencies automatically.</P>
+ <P>The <I>Makefiles</I> do not have the proper dependencies for
+ include files. You have to do a <I>make clean</I> and then another
+ <I>make</I>. If you are using <SMALL>GCC</SMALL> you can use the
+ <I>--enable-depend</I> option of <I>configure</I> to have the
+ compiler compute the dependencies automatically.</P>
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