4.7)How much database disk space is required to store data from a typical
text file?
- A PostgreSQL database may need six and a half times the disk space
+ A PostgreSQL database may need six-and-a-half times the disk space
required to store the data in a flat file.
Consider a file of 300,000 lines with two integers on each line. The
faster.
For column-specific optimization statistics, use VACUUM ANALYZE.
- VACUUM ANALYZE is important for complex multi-join queries, so the
+ VACUUM ANALYZE 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 VACUUM ANALYZE must be run to collect
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
- point, the system can more efficient answer queries like select all
- points within a bounding rectangle.
+ point, the system can more efficiently answer queries such as "select
+ all points within a bounding rectangle."
- The canonical paper that describes the original R-Tree design is:
+ The canonical paper that describes the original R-tree design is:
- Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial
+ 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.
You can also find this paper in Stonebraker's "Readings in Database
Systems"
- Builtin R-Trees can handle polygons and boxes. In theory, R-trees can
+ 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 require a bit of work and we don't currently have
+ extending R-trees requires a bit of work and we don't currently have
any documentation on how to do it.
4.12) What is Genetic Query Optimization?
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 non-exhaustive search.
+ join queries through nonexhaustive search.
4.13) How do I do regular expression searches and case-insensitive regular
expression searches?
- The ~ operator does regular-expression matching, and ~* does
- case-insensitive regular-expression matching. There is no
+ The ~ operator does regular expression matching, and ~* 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 LIKE with this:
WHERE lower(textfield) LIKE lower(pattern)
You will see the internal name when examining system catalogs and in
some error messages.
- The last four types above are "varlena" types (i.e. the first four
+ The last four types above are "varlena" types (i.e., the first four
bytes are the length, followed by the data). char(#) allocates the
maximum number of bytes no matter how much data is stored in the
field. text, varchar(#), and bytea all have variable length on the
You would then also have the new value stored in $newSerialID for use
in other queries (e.g., as a foreign key to the person table). Note
- that the name of the automatically-created SEQUENCE object will be
+ that the name of the automatically created SEQUENCE object will be
named <table>_<serialcolumn>_seq, where table and serialcolumn are the
names of your table and your SERIAL column, respectively.
- Alternatively, you could retrieve the just-assigned SERIAL value with
- the currval() function after it was inserted by default, e.g.,
+ Alternatively, you could retrieve the assigned SERIAL value with the
+ currval() function after it was inserted by default, e.g.,
INSERT INTO person (name) VALUES ('Blaise Pascal');
$newID = currval('person_id_seq');
Finally, you could use the OID returned from the INSERT statement to
- lookup the default value, though this is probably the least portable
+ 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 $sth->{pg_oid_status} after
$sth->execute().
OIDs are PostgreSQL's answer to unique row ids. Every row that is
created in PostgreSQL gets a unique OID. All OIDs generated during
initdb are less than 16384 (from backend/access/transam.h). All
- user-created OIDs are equal or greater that this. By default, all
- these OIDs are unique not only within a table, or database, but unique
+ user-created OIDs are equal to or greater than this. By default, all
+ these OIDs are unique not only within a table or database, but unique
within the entire PostgreSQL installation.
PostgreSQL uses OIDs in its internal system tables to link rows
4.23) Why are my subqueries using IN so slow?
- Currently, we join subqueries to outer queries by sequential scanning
- the result of the subquery for each row of the outer query. A
+ 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 IN with EXISTS:
SELECT *
FROM tab
dump core?
The problem could be a number of things. Try testing your user-defined
- function in a stand alone test program first.
+ function in a stand-alone test program first.
5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0 not in
alloc set!" mean?
<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
+A PostgreSQL database may need six-and-a-half times the disk space
required to store the data in a flat file.<P>
Consider a file of 300,000 lines with two integers on each line. The
For column-specific optimization statistics, use <SMALL>VACUUM
ANALYZE.</SMALL> <SMALL>VACUUM ANALYZE</SMALL> is important for complex
-multi-join queries, so the optimizer can estimate the number of rows
+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>
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 efficient answer queries like select all points
-within a bounding rectangle.<P>
+the system can more efficiently answer queries such as "select all points
+within a bounding rectangle.
"<P>
-The canonical paper that describes the original R-
Tree design is:<P>
+The canonical paper that describes the original R-
tree design is:<P>
-Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial Searching."
+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>
You can also find this paper in Stonebraker's "Readings in Database
Systems"<P>
-Builtin R-Trees can handle polygons and boxes. In theory, R-trees can
+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 require a bit of work and we don't currently have any
+extending R-trees requires a bit of work and we don't currently have any
documentation on how to do it.<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
-non
-exhaustive search.<P>
+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
+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:
<PRE>
You will see the internal name when examining system catalogs
and in some error messages.<P>
-The last four types above are "varlena" types (i.e. the first four bytes
+The last four types above are "varlena" types (i.e., the first four bytes
are the length, followed by the data). <I>char(#)</I> allocates the
maximum number of bytes no matter how much data is stored in the field.
<I>text, varchar(#),</I> and <I>bytea</I> all have variable length on the disk,
$newSerialID = nextval('person_id_seq');
INSERT INTO person (id, name) VALUES ($newSerialID, 'Blaise Pascal');
</PRE>
-You would then also have the new value stored in <CODE>$newSerialID</CODE> for use in other queries (e.g., as a foreign key to the <CODE>person</CODE> table). Note that the name of the automatically-created SEQUENCE object will be named <<I>table</I>>_<<I>serialcolumn</I>>_<I>seq</I>, where <I>table</I> and <I>serialcolumn</I> are the names of your table and your SERIAL column, respectively.
+
+You would then also have the new value stored in
+<CODE>$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 just-assigned SERIAL value with the <I>currval</I>() function <I>after</I> it was inserted by default, e.g.,
+Alternatively, you could retrieve the assigned SERIAL value with the <I>currval</I>() function <I>after</I> it was inserted by default, e.g.,
<PRE>
INSERT INTO person (name) VALUES ('Blaise Pascal');
$newID = currval('person_id_seq');
</PRE>
-Finally, you could use the <A HREF="#4.17"><small>OID</small></A> returned from the
-INSERT statement to lookup the default value, though this is probably
-the least portable approach. In Perl, using DBI with Edmund Mergl's
-DBD::Pg module, the oid value is made available via
+
+Finally, you could use the <A HREF="#4.17"><small>OID</small></A>
+returned from the INSERT statement to look up the default value, though
+this is probably the least portable approach. In Perl, using DBI with
+Edmund Mergl's DBD::Pg module, the oid value is made available via
<I>$sth->{pg_oid_status} after $sth->execute().</I>
<H4><A NAME="4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to
<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 or greater that 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>
+<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>
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
<P>
<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 sequential scanning
+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>:
<CODE><PRE>
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.
+function in a stand-alone test program first.
<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'ing</I> something that was not <I>palloc'ed.</I>
+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>
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