<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_index.sgml,v 1.31 2002/05/18 15:44:47 petere Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/create_index.sgml,v 1.70 2009/02/02 19:31:38 alvherre Exp $
PostgreSQL documentation
-->
<refentry id="SQL-CREATEINDEX">
<refmeta>
<refentrytitle id="sql-createindex-title">CREATE INDEX</refentrytitle>
+ <manvolnum>7</manvolnum>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
+
<refnamediv>
- <refname>
- CREATE INDEX
- </refname>
- <refpurpose>
- define a new index
- </refpurpose>
+ <refname>CREATE INDEX</refname>
+ <refpurpose>define a new index</refpurpose>
</refnamediv>
+
+ <indexterm zone="sql-createindex">
+ <primary>CREATE INDEX</primary>
+ </indexterm>
+
<refsynopsisdiv>
- <refsynopsisdivinfo>
- <date>2001-07-15</date>
- </refsynopsisdivinfo>
- <synopsis>
-CREATE [ UNIQUE ] INDEX <replaceable class="parameter">index_name</replaceable> ON <replaceable class="parameter">table</replaceable>
- [ USING <replaceable class="parameter">acc_method</replaceable> ] ( <replaceable class="parameter">column</replaceable> [ <replaceable class="parameter">ops_name</replaceable> ] [, ...] )
+<synopsis>
+CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] <replaceable class="parameter">name</replaceable> ON <replaceable class="parameter">table</replaceable> [ USING <replaceable class="parameter">method</replaceable> ]
+ ( { <replaceable class="parameter">column</replaceable> | ( <replaceable class="parameter">expression</replaceable> ) } [ <replaceable class="parameter">opclass</replaceable> ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )
+ [ WITH ( <replaceable class="PARAMETER">storage_parameter</replaceable> = <replaceable class="PARAMETER">value</replaceable> [, ... ] ) ]
+ [ TABLESPACE <replaceable class="parameter">tablespace</replaceable> ]
[ WHERE <replaceable class="parameter">predicate</replaceable> ]
-CREATE [ UNIQUE ] INDEX <replaceable class="parameter">index_name</replaceable> ON <replaceable class="parameter">table</replaceable>
- [ USING <replaceable class="parameter">acc_method</replaceable> ] ( <replaceable class="parameter">func_name</replaceable>( <replaceable class="parameter">column</replaceable> [, ... ]) [ <replaceable class="parameter">ops_name</replaceable> ] )
- [ WHERE <replaceable class="parameter">predicate</replaceable> ]
- </synopsis>
-
- <refsect2 id="R2-SQL-CREATEINDEX-1">
- <refsect2info>
- <date>1998-09-09</date>
- </refsect2info>
- <title>
- Inputs
- </title>
- <para>
+</synopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>
+ <command>CREATE INDEX</command> constructs an index named <replaceable
+ class="parameter">name</replaceable> on the specified table.
+ Indexes are primarily used to enhance database performance (though
+ inappropriate use can result in slower performance).
+ </para>
+
+ <para>
+ The key field(s) for the index are specified as column names,
+ or alternatively as expressions written in parentheses.
+ Multiple fields can be specified if the index method supports
+ multicolumn indexes.
+ </para>
+
+ <para>
+ An index field can be an expression computed from the values of
+ one or more columns of the table row. This feature can be used
+ to obtain fast access to data based on some transformation of
+ the basic data. For example, an index computed on
+ <literal>upper(col)</> would allow the clause
+ <literal>WHERE upper(col) = 'JIM'</> to use an index.
+ </para>
+
+ <para>
+ <productname>PostgreSQL</productname> provides the index methods
+ B-tree, hash, GiST, and GIN. Users can also define their own index
+ methods, but that is fairly complicated.
+ </para>
+
+ <para>
+ When the <literal>WHERE</literal> clause is present, a
+ <firstterm>partial index</firstterm> is created.
+ A partial index is an index that contains entries for only a portion of
+ a table, usually a portion that is more useful for indexing than the
+ rest of the table. For example, if you have a table that contains both
+ billed and unbilled orders where the unbilled orders take up a small
+ fraction of the total table and yet that is an often used section, you
+ can improve performance by creating an index on just that portion.
+ Another possible application is to use <literal>WHERE</literal> with
+ <literal>UNIQUE</literal> to enforce uniqueness over a subset of a
+ table. See <xref linkend="indexes-partial"> for more discussion.
+ </para>
+
+ <para>
+ The expression used in the <literal>WHERE</literal> clause can refer
+ only to columns of the underlying table, but it can use all columns,
+ not just the ones being indexed. Presently, subqueries and
+ aggregate expressions are also forbidden in <literal>WHERE</literal>.
+ The same restrictions apply to index fields that are expressions.
+ </para>
+
+ <para>
+ All functions and operators used in an index definition must be
+ <quote>immutable</>, that is, their results must depend only on
+ their arguments and never on any outside influence (such as
+ the contents of another table or the current time). This restriction
+ ensures that the behavior of the index is well-defined. To use a
+ user-defined function in an index expression or <literal>WHERE</literal>
+ clause, remember to mark the function immutable when you create it.
+ </para>
+ </refsect1>
+
+ <refsect1>
+ <title>Parameters</title>
<variablelist>
<varlistentry>
- <term>UNIQUE</term>
+ <term><literal>UNIQUE</literal></term>
+ <listitem>
+ <para>
+ Causes the system to check for
+ duplicate values in the table when the index is created (if data
+ already exist) and each time data is added. Attempts to
+ insert or update data which would result in duplicate entries
+ will generate an error.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>CONCURRENTLY</literal></term>
<listitem>
<para>
- Causes the system to check for
- duplicate values in the table when the index is created (if data
- already exist) and each time data is added. Attempts to
- insert or update data which would result in duplicate entries
- will generate an error.
+ When this option is used, <productname>PostgreSQL</> will build the
+ index without taking any locks that prevent concurrent inserts,
+ updates, or deletes on the table; whereas a standard index build
+ locks out writes (but not reads) on the table until it's done.
+ There are several caveats to be aware of when using this option
+ — see <xref linkend="SQL-CREATEINDEX-CONCURRENTLY"
+ endterm="SQL-CREATEINDEX-CONCURRENTLY-title">.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><replaceable class="parameter">index_name</replaceable></term>
+ <term><replaceable class="parameter">name</replaceable></term>
<listitem>
<para>
- The name of the index to be created. No schema name can be included
- here; the index is always created in the same schema as its parent
- table.
+ The name of the index to be created. No schema name can be included
+ here; the index is always created in the same schema as its parent
+ table.
</para>
</listitem>
</varlistentry>
<term><replaceable class="parameter">table</replaceable></term>
<listitem>
<para>
- The name (possibly schema-qualified) of the table to be indexed.
+ The name (possibly schema-qualified) of the table to be indexed.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><replaceable class="parameter">acc_method</replaceable></term>
+ <term><replaceable class="parameter">method</replaceable></term>
<listitem>
<para>
- The name of the access method to be used for the index. The
- default access method is <literal>BTREE</literal>.
- <application>PostgreSQL</application> provides four access
- methods for indexes:
-
- <variablelist>
- <varlistentry>
- <term><literal>BTREE</></term>
- <listitem>
- <para>
- an implementation of Lehman-Yao
- high-concurrency B-trees.
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term><literal>RTREE</></term>
- <listitem>
- <para>implements standard R-trees using Guttman's
- quadratic split algorithm.
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term><literal>HASH</></term>
- <listitem>
- <para>
- an implementation of Litwin's linear hashing.
- </para>
- </listitem>
- </varlistentry>
-
- <varlistentry>
- <term><literal>GIST</></term>
- <listitem>
- <para>
- Generalized Index Search Trees.
- </para>
- </listitem>
- </varlistentry>
- </variablelist>
+ The name of the index method to be used. Choices are
+ <literal>btree</literal>, <literal>hash</literal>,
+ <literal>gist</literal>, and <literal>gin</>. The
+ default method is <literal>btree</literal>.
</para>
</listitem>
</varlistentry>
<term><replaceable class="parameter">column</replaceable></term>
<listitem>
<para>
- The name of a column of the table.
+ The name of a column of the table.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><replaceable class="parameter">ops_name</replaceable></term>
+ <term><replaceable class="parameter">expression</replaceable></term>
<listitem>
<para>
- An associated operator class. See below for details.
+ An expression based on one or more columns of the table. The
+ expression usually must be written with surrounding parentheses,
+ as shown in the syntax. However, the parentheses can be omitted
+ if the expression has the form of a function call.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><replaceable class="parameter">func_name</replaceable></term>
+ <term><replaceable class="parameter">opclass</replaceable></term>
<listitem>
<para>
- A function, which returns a value that can be indexed.
+ The name of an operator class. See below for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><replaceable class="parameter">predicate</replaceable></term>
+ <term><literal>ASC</></term>
<listitem>
<para>
- Defines the constraint expression for a partial index.
+ Specifies ascending sort order (which is the default).
</para>
</listitem>
</varlistentry>
- </variablelist>
- </para>
- </refsect2>
- <refsect2 id="R2-SQL-CREATEINDEX-2">
- <refsect2info>
- <date>1998-09-09</date>
- </refsect2info>
- <title>
- Outputs
- </title>
- <para>
+ <varlistentry>
+ <term><literal>DESC</></term>
+ <listitem>
+ <para>
+ Specifies descending sort order.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>NULLS FIRST</></term>
+ <listitem>
+ <para>
+ Specifies that nulls sort before non-nulls. This is the default
+ when <literal>DESC</> is specified.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><literal>NULLS LAST</></term>
+ <listitem>
+ <para>
+ Specifies that nulls sort after non-nulls. This is the default
+ when <literal>DESC</> is not specified.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><replaceable class="parameter">storage_parameter</replaceable></term>
+ <listitem>
+ <para>
+ The name of an index-method-specific storage parameter. See
+ <xref linkend="sql-createindex-storage-parameters" endterm="sql-createindex-storage-parameters-title">
+ for details.
+ </para>
+ </listitem>
+ </varlistentry>
- <variablelist>
<varlistentry>
- <term><computeroutput>
-CREATE INDEX
- </computeroutput></term>
+ <term><replaceable class="parameter">tablespace</replaceable></term>
<listitem>
<para>
- The message returned if the index is successfully created.
+ The tablespace in which to create the index. If not specified,
+ <xref linkend="guc-default-tablespace"> is consulted, or
+ <xref linkend="guc-temp-tablespaces"> for indexes on temporary
+ tables.
</para>
</listitem>
</varlistentry>
<varlistentry>
- <term><computeroutput>
-ERROR: Cannot create index: 'index_name' already exists.
- </computeroutput></term>
+ <term><replaceable class="parameter">predicate</replaceable></term>
<listitem>
<para>
- This error occurs if it is impossible to create the index.
+ The constraint expression for a partial index.
</para>
</listitem>
</varlistentry>
+
</variablelist>
- </para>
- </refsect2>
- </refsynopsisdiv>
- <refsect1 id="R1-SQL-CREATEINDEX-1">
- <refsect1info>
- <date>1998-09-09</date>
- </refsect1info>
- <title>
- Description
- </title>
- <para>
- <command>CREATE INDEX</command> constructs an index
- <replaceable class="parameter">index_name</replaceable>
- on the specified <replaceable class="parameter">table</replaceable>.
-
- <tip>
- <para>
- Indexes are primarily used to enhance database performance.
- But inappropriate use will result in slower performance.
- </para>
- </tip>
- </para>
+ <refsect2 id="SQL-CREATEINDEX-storage-parameters">
+ <title id="SQL-CREATEINDEX-storage-parameters-title">Index Storage Parameters</title>
- <para>
- In the first syntax shown above, the key field(s) for the
- index are specified as column names.
- Multiple fields can be specified if the index access method supports
- multicolumn indexes.
- </para>
+ The <literal>WITH</> clause can specify <firstterm>storage parameters</>
+ for indexes. Each index method can have its own set of allowed storage
+ parameters. The <literal>B-tree</literal>, <literal>hash</literal> and
+ <literal>GiST</literal> built-in index methods all accept a single parameter:
+ </para>
- <para>
- In the second syntax shown above, an index is defined on the result
- of a user-specified function <replaceable
- class="parameter">func_name</replaceable> applied to one or more
- columns of a single table. These <firstterm>functional
- indexes</firstterm> can be used to obtain fast access to data based
- on operators that would normally require some transformation to apply
- them to the base data. For example, a functional index on
- <literal>upper(col)</> would allow the clause
- <literal>WHERE upper(col) = 'JIM'</> to use an index.
- </para>
+ <variablelist>
- <para>
- <application>PostgreSQL</application> provides B-tree, R-tree, hash,
- and GiST access methods for indexes. The B-tree access method is an
- implementation of Lehman-Yao high-concurrency B-trees. The R-tree
- access method implements standard R-trees using Guttman's quadratic
- split algorithm. The hash access method is an implementation of
- Litwin's linear hashing. We mention the algorithms used solely to
- indicate that all of these access methods are fully dynamic and do
- not have to be optimized periodically (as is the case with, for
- example, static hash access methods).
- </para>
+ <varlistentry>
+ <term><literal>FILLFACTOR</></term>
+ <listitem>
+ <para>
+ The fillfactor for an index is a percentage that determines how full
+ the index method will try to pack index pages. For B-trees, leaf pages
+ are filled to this percentage during initial index build, and also
+ when extending the index at the right (largest key values). If pages
+ subsequently become completely full, they will be split, leading to
+ gradual degradation in the index's efficiency. B-trees use a default
+ fillfactor of 90, but any value from 10 to 100 can be selected.
+ If the table is static then fillfactor 100 is best to minimize the
+ index's physical size, but for heavily updated tables a smaller
+ fillfactor is better to minimize the need for page splits. The
+ other index methods use fillfactor in different but roughly analogous
+ ways; the default fillfactor varies between methods.
+ </para>
+ </listitem>
+ </varlistentry>
- <para>
- When the <command>WHERE</command> clause is present, a
- <firstterm>partial index</firstterm> is created.
- A partial index is an index that contains entries for only a portion of
- a table, usually a portion that is somehow more interesting than the
- rest of the table. For example, if you have a table that contains both
- billed and unbilled orders where the unbilled orders take up a small
- fraction of the total table and yet that is an often used section, you
- can improve performance by creating an index on just that portion.
- Another possible application is to use <command>WHERE</command> with
- <command>UNIQUE</command> to enforce uniqueness over a subset of a
- table.
- </para>
+ </variablelist>
- <para>
- The expression used in the <command>WHERE</command> clause may refer
- only to columns of the underlying table (but it can use all columns,
- not only the one(s) being indexed). Presently, sub-SELECTs and
- aggregate expressions are also forbidden in <command>WHERE</command>.
- </para>
+ </refsect2>
- <para>
- All functions and operators used in an index definition must be
- <firstterm>immutable</>, that is, their results must depend only on
- their input arguments and never on any outside influence (such as
- the contents of another table or the current time). This restriction
- ensures that the behavior of the index is well-defined. To use a
- user-defined function in an index, remember to mark the function immutable
- when you create it.
- </para>
+ <refsect2 id="SQL-CREATEINDEX-CONCURRENTLY">
+ <title id="SQL-CREATEINDEX-CONCURRENTLY-title">Building Indexes Concurrently</title>
- <para>
- Use <xref linkend="sql-dropindex" endterm="sql-dropindex-title">
- to remove an index.
- </para>
+ <indexterm zone="SQL-CREATEINDEX-CONCURRENTLY">
+ <primary>index</primary>
+ <secondary>building concurrently</secondary>
+ </indexterm>
+
+ <para>
+ Creating an index can interfere with regular operation of a database.
+ Normally <productname>PostgreSQL</> locks the table to be indexed against
+ writes and performs the entire index build with a single scan of the
+ table. Other transactions can still read the table, but if they try to
+ insert, update, or delete rows in the table they will block until the
+ index build is finished. This could have a severe effect if the system is
+ a live production database. Very large tables can take many hours to be
+ indexed, and even for smaller tables, an index build can lock out writers
+ for periods that are unacceptably long for a production system.
+ </para>
- <refsect2 id="R2-SQL-CREATEINDEX-3">
- <refsect2info>
- <date>1998-09-09</date>
- </refsect2info>
- <title>
- Notes
- </title>
+ <para>
+ <productname>PostgreSQL</> supports building indexes without locking
+ out writes. This method is invoked by specifying the
+ <literal>CONCURRENTLY</> option of <command>CREATE INDEX</>.
+ When this option is used,
+ <productname>PostgreSQL</> must perform two scans of the table, and in
+ addition it must wait for all existing transactions that could potentially
+ use the index to terminate. Thus
+ this method requires more total work than a standard index build and takes
+ significantly longer to complete. However, since it allows normal
+ operations to continue while the index is built, this method is useful for
+ adding new indexes in a production environment. Of course, the extra CPU
+ and I/O load imposed by the index creation might slow other operations.
+ </para>
<para>
- The <productname>PostgreSQL</productname>
- query optimizer will consider using a B-tree index whenever
- an indexed attribute is involved in a comparison using one of:
-
- <simplelist type="inline">
- <member><</member>
- <member><=</member>
- <member>=</member>
- <member>>=</member>
- <member>></member>
- </simplelist>
+ In a concurrent index build, the index is actually entered into the
+ system catalogs in one transaction, then the two table scans occur in a
+ second and third transaction.
+ If a problem arises while scanning the table, such as a
+ uniqueness violation in a unique index, the <command>CREATE INDEX</>
+ command will fail but leave behind an <quote>invalid</> index. This index
+ will be ignored for querying purposes because it might be incomplete;
+ however it will still consume update overhead. The <application>psql</>
+ <command>\d</> command will mark such an index as <literal>INVALID</>:
+
+<programlisting>
+postgres=# \d tab
+ Table "public.tab"
+ Column | Type | Modifiers
+--------+---------+-----------
+ col | integer |
+Indexes:
+ "idx" btree (col) INVALID
+</programlisting>
+
+ The recommended recovery
+ method in such cases is to drop the index and try again to perform
+ <command>CREATE INDEX CONCURRENTLY</>. (Another possibility is to rebuild
+ the index with <command>REINDEX</>. However, since <command>REINDEX</>
+ does not support concurrent builds, this option is unlikely to seem
+ attractive.)
</para>
<para>
- The <productname>PostgreSQL</productname>
- query optimizer will consider using an R-tree index whenever
- an indexed attribute is involved in a comparison using one of:
-
- <simplelist type="inline">
- <member><<</member>
- <member>&<</member>
- <member>&></member>
- <member>>></member>
- <member>@</member>
- <member>~=</member>
- <member>&&</member>
- </simplelist>
+ Another caveat when building a unique index concurrently is that the
+ uniqueness constraint is already being enforced against other transactions
+ when the second table scan begins. This means that constraint violations
+ could be reported in other queries prior to the index becoming available
+ for use, or even in cases where the index build eventually fails. Also,
+ if a failure does occur in the second scan, the <quote>invalid</> index
+ continues to enforce its uniqueness constraint afterwards.
</para>
<para>
- The <productname>PostgreSQL</productname>
- query optimizer will consider using a hash index whenever
- an indexed attribute is involved in a comparison using
- the <literal>=</literal> operator.
+ Concurrent builds of expression indexes and partial indexes are supported.
+ Errors occurring in the evaluation of these expressions could cause
+ behavior similar to that described above for unique constraint violations.
</para>
<para>
- Currently, only the B-tree and gist access methods support multicolumn
- indexes. Up to 16 keys may be specified by default (this limit
- can be altered when building
- <application>PostgreSQL</application>). Only B-tree currently supports
- unique indexes.
+ Regular index builds permit other regular index builds on the
+ same table to occur in parallel, but only one concurrent index build
+ can occur on a table at a time. In both cases, no other types of schema
+ modification on the table are allowed meanwhile. Another difference
+ is that a regular <command>CREATE INDEX</> command can be performed within
+ a transaction block, but <command>CREATE INDEX CONCURRENTLY</> cannot.
</para>
+ </refsect2>
+ </refsect1>
+
+ <refsect1>
+ <title>Notes</title>
+
+ <para>
+ See <xref linkend="indexes"> for information about when indexes can
+ be used, when they are not used, and in which particular situations
+ they can be useful.
+ </para>
+
+ <para>
+ Currently, only the B-tree, GiST and GIN index methods support
+ multicolumn indexes. Up to 32 fields can be specified by default.
+ (This limit can be altered when building
+ <productname>PostgreSQL</productname>.) Only B-tree currently
+ supports unique indexes.
+ </para>
<para>
An <firstterm>operator class</firstterm> can be specified for each
used by the index for that column. For example, a B-tree index on
four-byte integers would use the <literal>int4_ops</literal> class;
this operator class includes comparison functions for four-byte
- integers. In practice the default operator class for the field's data
+ integers. In practice the default operator class for the column's data
type is usually sufficient. The main point of having operator classes
is that for some data types, there could be more than one meaningful
ordering. For example, we might want to sort a complex-number data
type either by absolute value or by real part. We could do this by
defining two operator classes for the data type and then selecting
- the proper class when making an index. There are also some operator
- classes with special purposes:
+ the proper class when making an index. More information about
+ operator classes is in <xref linkend="indexes-opclass"> and in <xref
+ linkend="xindex">.
+ </para>
- <itemizedlist>
- <listitem>
- <para>
- The operator classes <literal>box_ops</literal> and
- <literal>bigbox_ops</literal> both support R-tree indexes on the
- <literal>box</literal> data type.
- The difference between them is that <literal>bigbox_ops</literal>
- scales box coordinates down, to avoid floating-point exceptions from
- doing multiplication, addition, and subtraction on very large
- floating-point coordinates. (Note: this was true some time ago,
- but currently the two operator classes both use floating point
- and are effectively identical.)
- </para>
- </listitem>
- </itemizedlist>
+ <para>
+ For index methods that support ordered scans (currently, only B-tree),
+ the optional clauses <literal>ASC</>, <literal>DESC</>, <literal>NULLS
+ FIRST</>, and/or <literal>NULLS LAST</> can be specified to reverse
+ the normal sort direction of the index. Since an ordered index can be
+ scanned either forward or backward, it is not normally useful to create a
+ single-column <literal>DESC</> index — that sort ordering is already
+ available with a regular index. The value of these options is that
+ multicolumn indexes can be created that match the sort ordering requested
+ by a mixed-ordering query, such as <literal>SELECT ... ORDER BY x ASC, y
+ DESC</>. The <literal>NULLS</> options are useful if you need to support
+ <quote>nulls sort low</> behavior, rather than the default <quote>nulls
+ sort high</>, in queries that depend on indexes to avoid sorting steps.
</para>
- <para>
- The following query shows all defined operator classes:
-
- <programlisting>
-SELECT am.amname AS acc_method,
- opc.opcname AS ops_name,
- opr.oprname AS ops_comp
- FROM pg_am am, pg_opclass opc, pg_amop amop, pg_operator opr
- WHERE opc.opcamid = am.oid AND
- amop.amopclaid = opc.oid AND
- amop.amopopr = opr.oid
- ORDER BY acc_method, ops_name, ops_comp;
- </programlisting>
- </para>
- </refsect2>
+ <para>
+ For most index methods, the speed of creating an index is
+ dependent on the setting of <xref linkend="guc-maintenance-work-mem">.
+ Larger values will reduce the time needed for index creation, so long
+ as you don't make it larger than the amount of memory really available,
+ which would drive the machine into swapping. For hash indexes, the
+ value of <xref linkend="guc-effective-cache-size"> is also relevant to
+ index creation time: <productname>PostgreSQL</productname> will use one
+ of two different hash index creation methods depending on whether the
+ estimated index size is more or less than <varname>effective_cache_size</>.
+ For best results, make sure that this parameter is also set to something
+ reflective of available memory, and be careful that the sum of
+ <varname>maintenance_work_mem</> and <varname>effective_cache_size</> is
+ less than the machine's RAM less whatever space is needed by other
+ programs.
+ </para>
+
+ <para>
+ Use <xref linkend="sql-dropindex" endterm="sql-dropindex-title">
+ to remove an index.
+ </para>
+
+ <para>
+ Prior releases of <productname>PostgreSQL</productname> also had an
+ R-tree index method. This method has been removed because
+ it had no significant advantages over the GiST method.
+ If <literal>USING rtree</> is specified, <command>CREATE INDEX</>
+ will interpret it as <literal>USING gist</>, to simplify conversion
+ of old databases to GiST.
+ </para>
</refsect1>
- <refsect1 id="R1-SQL-CREATEINDEX-2">
- <title>
- Usage
- </title>
- <para>To create a B-tree index on the field <literal>title</literal>
- in the table <literal>films</literal>:
+ <refsect1>
+ <title>Examples</title>
+
+ <para>
+ To create a B-tree index on the column <literal>title</literal> in
+ the table <literal>films</literal>:
+<programlisting>
+CREATE UNIQUE INDEX title_idx ON films (title);
+</programlisting>
+ </para>
+
+ <para>
+ To create an index on the expression <literal>lower(title)</>,
+ allowing efficient case-insensitive searches:
+<programlisting>
+CREATE INDEX lower_title_idx ON films ((lower(title)));
+</programlisting>
+ </para>
+
+ <para>
+ To create an index with non-default sort ordering of nulls:
+<programlisting>
+CREATE INDEX title_idx_nulls_low ON films (title NULLS FIRST);
+</programlisting>
+ </para>
+
+ <para>
+ To create an index with non-default fill factor:
+<programlisting>
+CREATE UNIQUE INDEX title_idx ON films (title) WITH (fillfactor = 70);
+</programlisting>
+ </para>
+
+ <para>
+ To create an index on the column <literal>code</> in the table
+ <literal>films</> and have the index reside in the tablespace
+ <literal>indexspace</>:
+<programlisting>
+CREATE INDEX code_idx ON films(code) TABLESPACE indexspace;
+</programlisting>
</para>
- <programlisting>
-CREATE UNIQUE INDEX title_idx
- ON films (title);
- </programlisting>
<!--
<comment>
Is this example correct?
</comment>
<para>
- To create a R-tree index on a point attribute so that we
+ To create a GiST index on a point attribute so that we
can efficiently use box operators on the result of the
conversion function:
- </para>
<programlisting>
CREATE INDEX pointloc
- ON points USING RTREE (point2box(location) box_ops);
+ ON points USING GIST (point2box(location) box_ops);
SELECT * FROM points
WHERE point2box(points.pointloc) = boxes.box;
</programlisting>
+ </para>
-->
+ <para>
+ To create an index without locking out writes to the table:
+<programlisting>
+CREATE INDEX CONCURRENTLY sales_quantity_index ON sales_table (quantity);
+</programlisting>
+ </para>
+
</refsect1>
-
- <refsect1 id="R1-SQL-CREATEINDEX-3">
- <title>
- Compatibility
- </title>
-
- <refsect2 id="R2-SQL-CREATEINDEX-4">
- <refsect2info>
- <date>1998-09-09</date>
- </refsect2info>
- <title>
- SQL92
- </title>
- <para>
- CREATE INDEX is a <productname>PostgreSQL</productname> language extension.
- </para>
- <para>
- There is no <command>CREATE INDEX</command> command in SQL92.
- </para>
- </refsect2>
+
+ <refsect1>
+ <title>Compatibility</title>
+
+ <para>
+ <command>CREATE INDEX</command> is a
+ <productname>PostgreSQL</productname> language extension. There
+ are no provisions for indexes in the SQL standard.
+ </para>
</refsect1>
-</refentry>
-<!-- Keep this comment at the end of the file
-Local variables:
-mode: sgml
-sgml-omittag:nil
-sgml-shorttag:t
-sgml-minimize-attributes:nil
-sgml-always-quote-attributes:t
-sgml-indent-step:1
-sgml-indent-data:t
-sgml-parent-document:nil
-sgml-default-dtd-file:"../reference.ced"
-sgml-exposed-tags:nil
-sgml-local-catalogs:"/usr/lib/sgml/catalog"
-sgml-local-ecat-files:nil
-End:
--->
+ <refsect1>
+ <title>See Also</title>
+
+ <simplelist type="inline">
+ <member><xref linkend="sql-alterindex" endterm="sql-alterindex-title"></member>
+ <member><xref linkend="sql-dropindex" endterm="sql-dropindex-title"></member>
+ </simplelist>
+ </refsect1>
+</refentry>
OSDN Git Service
