Postgresql 中文操作指南

CREATE INDEX

CREATE INDEX — 定义新索引

CREATE INDEX — define a new index

Synopsis

CREATE [ UNIQUE ] INDEX [ CONCURRENTLY ] [ [ IF NOT EXISTS ] name ] ON [ ONLY ] table_name [ USING method ]
    ( { column_name | ( expression ) } [ COLLATE collation ] [ opclass [ ( opclass_parameter = value [, ... ] ) ] ] [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] )
    [ INCLUDE ( column_name [, ...] ) ]
    [ NULLS [ NOT ] DISTINCT ]
    [ WITH ( storage_parameter [= value] [, ... ] ) ]
    [ TABLESPACE tablespace_name ]
    [ WHERE predicate ]

Description

CREATE INDEX 为指定关系（可以是表或物化视图）的指定列构建索引。索引主要用于提高数据库性能（尽管使用不当会导致性能降低）。

CREATE INDEX constructs an index on the specified column(s) of the specified relation, which can be a table or a materialized view. Indexes are primarily used to enhance database performance (though inappropriate use can result in slower performance).

索引的关键字段指定为列名，或者指定为括号中编写的表达式。如果索引方法支持多列索引，则可以指定多个字段。

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.

索引字段可以是根据表行的列值计算的表达式。此功能可用于基于基本数据的一些转换快速访问数据。例如，在 upper(col) 上计算索引将允许子句 WHERE upper(col) = 'JIM' 使用索引。

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 upper(col) would allow the clause WHERE upper(col) = 'JIM' to use an index.

PostgreSQL 提供 B 树、哈希、GiST、SP-GiST、GIN 和 BRIN 索引方法。用户还可以定义自己的索引方法，但这非常复杂。

PostgreSQL provides the index methods B-tree, hash, GiST, SP-GiST, GIN, and BRIN. Users can also define their own index methods, but that is fairly complicated.

当存在 WHERE 子句时，将创建 partial index 。部分索引是一个索引，其中仅包含表的某一部分的条目，通常是比表的其它部分更适合于编制索引的那一部分。例如，如果你有一个包含已开票和未开票订单的表，其中未开票订单占总表的很小一部分，但仍是经常使用的一部分，则可以通过仅在该部分上创建索引来提高性能。另一个可能的应用是使用 WHERE 和 UNIQUE 对表的子集强制唯一性。有关更多讨论，请参见 Section 11.8 。

When the WHERE clause is present, a partial index 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 WHERE with UNIQUE to enforce uniqueness over a subset of a table. See Section 11.8 for more discussion.

WHERE 子句中使用的表达式只能引用基础表中的列，但它可以使用所有列，不仅仅是正在编制索引的列。目前，在 WHERE 中子查询和聚合表达式也被禁止。相同限制适用于作为表达式的索引字段。

The expression used in the WHERE 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 WHERE. The same restrictions apply to index fields that are expressions.

在索引定义中所使用的所有函数和运算符都必须是“不变的”，即，其结果必须只取决于其参数，并且永远不会依赖任何外部影响（例如其他表的表内容或当前时间）。这个限制确保了索引的行为是明确定义的。要在索引表达或 WHERE 子句中使用用户定义的函数，请记住在创建函数时标记该函数为不变。

All functions and operators used in an index definition must be “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 WHERE clause, remember to mark the function immutable when you create it.

Parameters

  • UNIQUE

    • 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.

    • Additional restrictions apply when unique indexes are applied to partitioned tables; see CREATE TABLE.

  • CONCURRENTLY

    • When this option is used, 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 Building Indexes Concurrently below.

    • For temporary tables, CREATE INDEX is always non-concurrent, as no other session can access them, and non-concurrent index creation is cheaper.

  • IF NOT EXISTS

    • Do not throw an error if a relation with the same name already exists. A notice is issued in this case. Note that there is no guarantee that the existing index is anything like the one that would have been created. Index name is required when IF NOT EXISTS is specified.

  • INCLUDE

    • The optional INCLUDE clause specifies a list of columns which will be included in the index as non-key columns. A non-key column cannot be used in an index scan search qualification, and it is disregarded for purposes of any uniqueness or exclusion constraint enforced by the index. However, an index-only scan can return the contents of non-key columns without having to visit the index’s table, since they are available directly from the index entry. Thus, addition of non-key columns allows index-only scans to be used for queries that otherwise could not use them.

    • It’s wise to be conservative about adding non-key columns to an index, especially wide columns. If an index tuple exceeds the maximum size allowed for the index type, data insertion will fail. In any case, non-key columns duplicate data from the index’s table and bloat the size of the index, thus potentially slowing searches. Furthermore, B-tree deduplication is never used with indexes that have a non-key column.

    • Columns listed in the INCLUDE clause don’t need appropriate operator classes; the clause can include columns whose data types don’t have operator classes defined for a given access method.

    • Expressions are not supported as included columns since they cannot be used in index-only scans.

    • Currently, the B-tree, GiST and SP-GiST index access methods support this feature. In these indexes, the values of columns listed in the INCLUDE clause are included in leaf tuples which correspond to heap tuples, but are not included in upper-level index entries used for tree navigation.

  • name

    • 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 must be distinct from the name of any other relation (table, sequence, index, view, materialized view, or foreign table) in that schema. If the name is omitted, PostgreSQL chooses a suitable name based on the parent table’s name and the indexed column name(s).

  • ONLY

    • Indicates not to recurse creating indexes on partitions, if the table is partitioned. The default is to recurse.

  • table_name

    • The name (possibly schema-qualified) of the table to be indexed.

  • method

    • The name of the index method to be used. Choices are btree, hash, gist, spgist, gin, brin, or user-installed access methods like bloom. The default method is btree.

  • column_name

    • The name of a column of the table.

  • expression

    • 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.

  • collation

    • The name of the collation to use for the index. By default, the index uses the collation declared for the column to be indexed or the result collation of the expression to be indexed. Indexes with non-default collations can be useful for queries that involve expressions using non-default collations.

  • opclass

    • The name of an operator class. See below for details.

  • opclass_parameter

    • The name of an operator class parameter. See below for details.

  • ASC

    • Specifies ascending sort order (which is the default).

  • DESC

    • Specifies descending sort order.

  • NULLS FIRST

    • Specifies that nulls sort before non-nulls. This is the default when DESC is specified.

  • NULLS LAST

    • Specifies that nulls sort after non-nulls. This is the default when DESC is not specified.

  • NULLS DISTINCT__NULLS NOT DISTINCT

    • Specifies whether for a unique index, null values should be considered distinct (not equal). The default is that they are distinct, so that a unique index could contain multiple null values in a column.

  • storage_parameter

  • tablespace_name

  • predicate

    • The constraint expression for a partial index.

Index Storage Parameters

可选的 WITH 子句为索引指定 storage parameters 。每个索引方法都有其自身的一组允许的存储参数。B 树、哈希、GiST 和 SP-GiST 索引方法都接受此参数：

The optional WITH clause specifies storage parameters for the index. Each index method has its own set of allowed storage parameters. The B-tree, hash, GiST and SP-GiST index methods all accept this parameter:

  • fillfactor (integer) #

    • 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 builds, and also when extending the index at the right (adding new largest key values). If pages subsequently become completely full, they will be split, leading to fragmentation of the on-disk index structure. B-trees use a default fillfactor of 90, but any integer value from 10 to 100 can be selected.

    • B-tree indexes on tables where many inserts and/or updates are anticipated can benefit from lower fillfactor settings at CREATE INDEX time (following bulk loading into the table). Values in the range of 50 - 90 can usefully “smooth out” the rate of page splits during the early life of the B-tree index (lowering fillfactor like this may even lower the absolute number of page splits, though this effect is highly workload dependent). The B-tree bottom-up index deletion technique described in Section 67.4.2 is dependent on having some “extra” space on pages to store “extra” tuple versions, and so can be affected by fillfactor (though the effect is usually not significant).

    • In other specific cases it might be useful to increase fillfactor to 100 at CREATE INDEX time as a way of maximizing space utilization. You should only consider this when you are completely sure that the table is static (i.e. that it will never be affected by either inserts or updates). A fillfactor setting of 100 otherwise risks harming performance: even a few updates or inserts will cause a sudden flood of page splits.

    • The other index methods use fillfactor in different but roughly analogous ways; the default fillfactor varies between methods.

B 树索引还接受此参数：

B-tree indexes additionally accept this parameter:

  • deduplicate_items (boolean) #

    • Controls usage of the B-tree deduplication technique described in Section 67.4.3. Set to ON or OFF to enable or disable the optimization. (Alternative spellings of ON and OFF are allowed as described in Section 20.1.) The default is ON.

Note

通过 ALTER INDEX 关闭 deduplicate_items 可防止将来插入触发去重，但本身不会使现有的发布列表元组使用标准元组表示形式。

Turning deduplicate_items off via ALTER INDEX prevents future insertions from triggering deduplication, but does not in itself make existing posting list tuples use the standard tuple representation.

GiST 索引还接受此参数：

GiST indexes additionally accept this parameter:

  • buffering (enum) #

    • Determines whether the buffered build technique described in Section 68.4.1 is used to build the index. With OFF buffering is disabled, with ON it is enabled, and with AUTO it is initially disabled, but is turned on on-the-fly once the index size reaches effective_cache_size. The default is AUTO. Note that if sorted build is possible, it will be used instead of buffered build unless buffering=ON is specified.

GIN 索引接受不同的参数：

GIN indexes accept different parameters:

  • fastupdate (boolean) #

    • This setting controls usage of the fast update technique described in Section 70.4.1. It is a Boolean parameter: ON enables fast update, OFF disables it. The default is ON.

Note

通过 ALTER INDEX 关闭 fastupdate 会阻止将将来的插入操作添加到待处理索引项列表中，但本身不会刷新以前的项。你可能希望 VACUUM 表或调用 gin_clean_pending_list 函数，以确保已清空待处理列表。

Turning fastupdate off via ALTER INDEX prevents future insertions from going into the list of pending index entries, but does not in itself flush previous entries. You might want to VACUUM the table or call gin_clean_pending_list function afterward to ensure the pending list is emptied.

  • gin_pending_list_limit (integer) #

BRIN 索引接受不同的参数：

BRIN indexes accept different parameters:

  • pages_per_range (integer) #

    • Defines the number of table blocks that make up one block range for each entry of a BRIN index (see Section 71.1 for more details). The default is 128.

  • autosummarize (boolean) #

    • Defines whether a summarization run is queued for the previous page range whenever an insertion is detected on the next one. See Section 71.1.1 for more details. The default is off.

Building Indexes Concurrently

创建索引可能会干扰数据库的常规操作。PostgreSQL 通常将要编制索引的表锁定，以防写入，并使用表的单次扫描执行整个索引构建。其他事务仍可以读取表，但如果它们尝试在表中插入、更新或删除行，它们将阻塞，直到索引构建完成。如果该系统是一个实时生产数据库，则可能会产生严重的影响。非常大的表可能需要很多小时才能编制索引，即使对于较小的表，索引构建也会将写入者锁定一段时期，而这对于生产系统来说是不可接受的。

Creating an index can interfere with regular operation of a database. Normally 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.

PostgreSQL 支持在不锁定写入的情况下构建索引。此方法通过指定 CREATE INDEX 的 CONCURRENTLY 选项来调用。当使用此选项时，PostgreSQL 必须对表执行两次扫描，此外，它还必须等待所有可能修改或使用索引的现有事务终止。因此，此方法比标准索引构建需要更多总工作，并且需要更长的时间才能完成。但是，由于它允许在构建索引时继续进行正常操作，因此此方法可用于在生产环境中添加新索引。当然，索引创建所施加的额外 CPU 和 I/O 负载可能会减慢其他操作。

PostgreSQL supports building indexes without locking out writes. This method is invoked by specifying the CONCURRENTLY option of CREATE INDEX. When this option is used, PostgreSQL must perform two scans of the table, and in addition it must wait for all existing transactions that could potentially modify or 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.

在并发索引构建中，索引实际上作为一个“无效”索引进入到一个事务中的系统目录中，然后在两个以上的其他事务中发生两次表扫描。在每次表扫描前，索引构建必须等待已修改该表的现有事务终止。在第二次扫描后，索引构建必须等待任何具有早于第二次扫描的快照（参阅 Chapter 13 ）的事务终止，包括由其他表上并发索引构建的任何阶段使用的交易，如果涉及索引是部分的或具有不是简单列引用的列。然后，最终索引可以被标记为“有效”并准备好使用，并且 CREATE INDEX 命令终止。然而，即使这样，索引可能也无法立即用于查询：在最坏的情况下，只要早于索引构建开始的事务存在，就无法使用它。

In a concurrent index build, the index is actually entered as an “invalid” index into the system catalogs in one transaction, then two table scans occur in two more transactions. Before each table scan, the index build must wait for existing transactions that have modified the table to terminate. After the second scan, the index build must wait for any transactions that have a snapshot (see Chapter 13) predating the second scan to terminate, including transactions used by any phase of concurrent index builds on other tables, if the indexes involved are partial or have columns that are not simple column references. Then finally the index can be marked “valid” and ready for use, and the CREATE INDEX command terminates. Even then, however, the index may not be immediately usable for queries: in the worst case, it cannot be used as long as transactions exist that predate the start of the index build.

如果在扫描表时出现问题，例如死锁或唯一索引中的唯一性违规，则 CREATE INDEX 命令将失败，但会留下“无效”索引。此索引将因可能是 incomplete 而被忽略用于查询目的；但是，它仍会消耗更新开销。psql \d 命令会将这样的索引报告为 INVALID ：

If a problem arises while scanning the table, such as a deadlock or a uniqueness violation in a unique index, the CREATE INDEX command will fail but leave behind an “invalid” index. This index will be ignored for querying purposes because it might be incomplete; however it will still consume update overhead. The psql \d command will report such an index as INVALID:

postgres=# \d tab
       Table "public.tab"
 Column |  Type   | Collation | Nullable | Default
--------+---------+-----------+----------+---------
 col    | integer |           |          |
Indexes:
    "idx" btree (col) INVALID

在这种情况下，推荐的恢复方法是删除索引并尝试再次执行 CREATE INDEX CONCURRENTLY 。（另一种可能性是用 REINDEX INDEX CONCURRENTLY 重新构建索引。）

The recommended recovery method in such cases is to drop the index and try again to perform CREATE INDEX CONCURRENTLY. (Another possibility is to rebuild the index with REINDEX INDEX CONCURRENTLY).

在并发构建唯一索引时的另一个需要注意的地方是，当第二个表扫描开始时，唯一性约束已对其他事务强制执行。这意味着在索引可用于使用之前，其他查询中可能会报告约束违规，甚至是在索引构建最终失败的情况下。此外，如果在第二次扫描中确实发生故障，则“无效”索引会继续在之后强制执行其唯一性约束。

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 “invalid” index continues to enforce its uniqueness constraint afterwards.

表达式索引和部分索引的并发构建得到支持。在计算这些表达式时发生的错误可能会导致类似于上面针对唯一约束违规描述的行为。

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.

常规索引构建允许在同一表上对其他常规索引构建同时发生，但一次只允许在表上发生一个并发索引构建。在这两种情况下，在构建索引时都不允许修改表的模式。另一个区别在于，常规 CREATE INDEX 命令可以在事务块内执行，但 CREATE INDEX CONCURRENTLY 则不行。

Regular index builds permit other regular index builds on the same table to occur simultaneously, but only one concurrent index build can occur on a table at a time. In either case, schema modification of the table is not allowed while the index is being built. Another difference is that a regular CREATE INDEX command can be performed within a transaction block, but CREATE INDEX CONCURRENTLY cannot.

当前不支持对分区表的索引进行并发构建。但是，你可以分别对各个分区并发构建索引，然后最终以非并发方式创建分区索引，以减少锁定对分区表写入的时间。在这种情况下，构建分区索引是仅元数据的操作。

Concurrent builds for indexes on partitioned tables are currently not supported. However, you may concurrently build the index on each partition individually and then finally create the partitioned index non-concurrently in order to reduce the time where writes to the partitioned table will be locked out. In this case, building the partitioned index is a metadata only operation.

Notes

参阅 Chapter 11 ，了解有关何时可以使用索引、何时不使用索引以及在哪些特定情况下它们会有用的信息。

See Chapter 11 for information about when indexes can be used, when they are not used, and in which particular situations they can be useful.

目前，只有 B 树、GiST、GIN 和 BRIN 索引方法支持多键列索引。是否可以有多个键列与是否可以将 INCLUDE 列添加到索引中无关。索引最多可以有 32 列，包括 INCLUDE 列。（在构建 PostgreSQL 时可以更改此限制。）目前只有 B 树支持唯一索引。

Currently, only the B-tree, GiST, GIN, and BRIN index methods support multiple-key-column indexes. Whether there can be multiple key columns is independent of whether INCLUDE columns can be added to the index. Indexes can have up to 32 columns, including INCLUDE columns. (This limit can be altered when building PostgreSQL.) Only B-tree currently supports unique indexes.

可以为索引的每一列指定带有可选参数的 operator class 。运算符类标识用于索引针对该列的运算符。例如，基于四字节整数的 B 树索引将使用 int4_ops 类；此运算符类包括用于四字节整数的比较函数。在实践中，列的数据类型的默认运算符类通常是足够的。具有运算符类的主要目的在于，对于某些数据类型，可能存在多种有意义的排序顺序。例如，我们可能希望按绝对值或实部两种方式对复数数据类型进行排序。我们可以通过为数据类型定义两个运算符类，然后在创建索引时选择适当的类来做到这一点。关于运算符类的更多信息在 Section 11.10 和 Section 38.16 中。

An operator class with optional parameters can be specified for each column of an index. The operator class identifies the operators to be used by the index for that column. For example, a B-tree index on four-byte integers would use the int4_ops class; this operator class includes comparison functions for four-byte 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 creating an index. More information about operator classes is in Section 11.10 and in Section 38.16.

当对分区表调用 CREATE INDEX 时，默认 behavior 是递归遍历所有分区以确保它们都具有匹配的索引。首先检查每个分区以确定是否已存在等效索引，如果存在，该索引将作为分区索引附加到正在创建的索引中，该索引将成为它的父索引。如果不存在匹配的索引，则将创建一个新索引并自动附加；每个分区中新索引的名称将被确定，就好像命令中未指定索引名称一样。如果指定了 ONLY 选项，则不会执行递归，并且索引会被标记为无效。（一旦所有分区获取匹配的索引， ALTER INDEX …​ ATTACH PARTITION 将标记索引为有效。）但是，请注意，无论是否指定了 ONLY ，使用 CREATE TABLE …​ PARTITION OF 创建的任何未来的分区都会自动拥有匹配的索引。

When CREATE INDEX is invoked on a partitioned table, the default behavior is to recurse to all partitions to ensure they all have matching indexes. Each partition is first checked to determine whether an equivalent index already exists, and if so, that index will become attached as a partition index to the index being created, which will become its parent index. If no matching index exists, a new index will be created and automatically attached; the name of the new index in each partition will be determined as if no index name had been specified in the command. If the ONLY option is specified, no recursion is done, and the index is marked invalid. (ALTER INDEX …​ ATTACH PARTITION marks the index valid, once all partitions acquire matching indexes.) Note, however, that any partition that is created in the future using CREATE TABLE …​ PARTITION OF will automatically have a matching index, regardless of whether ONLY is specified.

对于支持有序扫描的索引方法（目前仅限 B-tree），可以指定可选子句 ASC 、 DESC 、 NULLS FIRST 和/或 NULLS LAST 来修改索引的排序顺序。由于有序索引可以在向前或向后扫描，因此通常无须创建单列 DESC 索引——常规索引中已经提供了该排序顺序。这些选项的价值在于，可以创建匹配混合排序查询（例如 SELECT …​ ORDER BY x ASC, y DESC ）所请求的排序顺序的多列索引。如果您需要支持“nulls sort low”行为（而不是在依赖索引以避免排序步骤的查询中的默认“nulls sort high”）， NULLS 选项将非常有用。

For index methods that support ordered scans (currently, only B-tree), the optional clauses ASC, DESC, NULLS FIRST, and/or NULLS LAST can be specified to modify the sort ordering of the index. Since an ordered index can be scanned either forward or backward, it is not normally useful to create a single-column 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 SELECT …​ ORDER BY x ASC, y DESC. The NULLS options are useful if you need to support “nulls sort low” behavior, rather than the default “nulls sort high”, in queries that depend on indexes to avoid sorting steps.

系统会定期收集表所有列的统计信息。新创建的非表达式索引可以立即使用这些统计信息来确定索引的有效性。对于新的表达式索引，有必要运行 ANALYZE 或等待 autovacuum daemon 分析表以生成这些索引的统计信息。

The system regularly collects statistics on all of a table’s columns. Newly-created non-expression indexes can immediately use these statistics to determine an index’s usefulness. For new expression indexes, it is necessary to run ANALYZE or wait for the autovacuum daemon to analyze the table to generate statistics for these indexes.

对于大多数索引方法，创建索引的速度取决于 maintenance_work_mem 设置。只要不将其设置为大于实际可用内存量（这会导致机器进行交换），较大的值将减少创建索引所需的时间。

For most index methods, the speed of creating an index is dependent on the setting of 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.

PostgreSQL 可以在利用多颗 CPU 处理表行时构建索引，以更快地处理表行。此功能称为 parallel index build 。对于支持并行构建索引的索引方法（目前仅限 B-tree）， maintenance_work_mem 指定可以被每个索引构建操作整体使用的最大内存量，而不论启动了多少个工作进程。通常，成本模型会自动确定是否应该请求多个工作进程。

PostgreSQL can build indexes while leveraging multiple CPUs in order to process the table rows faster. This feature is known as parallel index build. For index methods that support building indexes in parallel (currently, only B-tree), maintenance_work_mem specifies the maximum amount of memory that can be used by each index build operation as a whole, regardless of how many worker processes were started. Generally, a cost model automatically determines how many worker processes should be requested, if any.

并行索引构建可能会受益于增加 maintenance_work_mem ，而等效的串行索引构建几乎不会或根本不会受益。请注意， maintenance_work_mem 可能会影响所请求的工作进程数量，因为并行工作进程必须至少占 maintenance_work_mem 预算的 32MB 份额。领导者进程还必须占有剩余的 32MB 份额。增加 max_parallel_maintenance_workers 可能会允许使用更多的工作进程，这将减少创建索引所需的时间，只要索引构建尚未被 I/O 绑定。当然，还应该有闲置的足够 CPU 容量。

Parallel index builds may benefit from increasing maintenance_work_mem where an equivalent serial index build will see little or no benefit. Note that maintenance_work_mem may influence the number of worker processes requested, since parallel workers must have at least a 32MB share of the total maintenance_work_mem budget. There must also be a remaining 32MB share for the leader process. Increasing max_parallel_maintenance_workers may allow more workers to be used, which will reduce the time needed for index creation, so long as the index build is not already I/O bound. Of course, there should also be sufficient CPU capacity that would otherwise lie idle.

通过 ALTER TABLE 设置 parallel_workers 的值可以直接控制 CREATE INDEX 将针对该表请求多少个并行工作进程。这完全绕过了成本模型并阻止 maintenance_work_mem 影响所请求的并行工作进程数量。通过 ALTER TABLE 将 parallel_workers 设置为 0 将在所有情况下禁用表上的并行索引构建。

Setting a value for parallel_workers via ALTER TABLE directly controls how many parallel worker processes will be requested by a CREATE INDEX against the table. This bypasses the cost model completely, and prevents maintenance_work_mem from affecting how many parallel workers are requested. Setting parallel_workers to 0 via ALTER TABLE will disable parallel index builds on the table in all cases.

Tip

您可能希望在将 parallel_workers 设置为调整索引构建的一部分之后对其进行重置。这样做可以避免查询计划的无意更改，因为 parallel_workers 会影响 all 并行表扫描。

You might want to reset parallel_workers after setting it as part of tuning an index build. This avoids inadvertent changes to query plans, since parallel_workers affects all parallel table scans.

虽然 CREATE INDEX 与 CONCURRENTLY 选项支持无需特殊限制的并行构建，但实际上只有第一次表扫描是并行执行的。

While CREATE INDEX with the CONCURRENTLY option supports parallel builds without special restrictions, only the first table scan is actually performed in parallel.

使用 DROP INDEX 删除索引。

Use DROP INDEX to remove an index.

与任何长期运行的事务一样，针对某个表的 CREATE INDEX 可能会影响在任何其他表上由并发 VACUUM 可以删除哪些元组。

Like any long-running transaction, CREATE INDEX on a table can affect which tuples can be removed by concurrent VACUUM on any other table.

PostgreSQL 的早期版本也有一个 R-tree 索引方法。该方法已被删除，因为它相对于 GiST 方法没有重大优势。如果指定了 USING rtree ， CREATE INDEX 会将其解释为 USING gist ，以简化将旧数据库转换为 GiST 的过程。

Prior releases of PostgreSQL also had an R-tree index method. This method has been removed because it had no significant advantages over the GiST method. If USING rtree is specified, CREATE INDEX will interpret it as USING gist, to simplify conversion of old databases to GiST.

每个运行 CREATE INDEX 的后端将在 pg_stat_progress_create_index 视图中报告其进度。有关详细信息，请参阅 Section 28.4.4 。

Each backend running CREATE INDEX will report its progress in the pg_stat_progress_create_index view. See Section 28.4.4 for details.

Examples

在表 films 中的列 title 上创建唯一的 B-tree 索引：

To create a unique B-tree index on the column title in the table films:

CREATE UNIQUE INDEX title_idx ON films (title);

在表 films 中的列 title 上创建具有已包含列 director 和 rating 的唯一 B-tree 索引：

To create a unique B-tree index on the column title with included columns director and rating in the table films:

CREATE UNIQUE INDEX title_idx ON films (title) INCLUDE (director, rating);

创建禁用重复消除的 B-Tree 索引：

To create a B-Tree index with deduplication disabled:

CREATE INDEX title_idx ON films (title) WITH (deduplicate_items = off);

在表达式 lower(title) 上创建一个索引，允许高效的不区分大小写的搜索：

To create an index on the expression lower(title), allowing efficient case-insensitive searches:

CREATE INDEX ON films ((lower(title)));

（在此示例中，我们选择不使用索引名称，因此系统会选择一个名称，通常为 films_lower_idx 。）

(In this example we have chosen to omit the index name, so the system will choose a name, typically films_lower_idx.)

使用非默认排序规则创建索引：

To create an index with non-default collation:

CREATE INDEX title_idx_german ON films (title COLLATE "de_DE");

创建具有非默认排序顺序的空值的索引：

To create an index with non-default sort ordering of nulls:

CREATE INDEX title_idx_nulls_low ON films (title NULLS FIRST);

创建具有非默认填充因子的索引：

To create an index with non-default fill factor:

CREATE UNIQUE INDEX title_idx ON films (title) WITH (fillfactor = 70);

创建禁用了快速更新的 GIN 索引：

To create a GIN index with fast updates disabled:

CREATE INDEX gin_idx ON documents_table USING GIN (locations) WITH (fastupdate = off);

在表 films 中的列 code 上创建索引，并将该索引驻留在表空间 indexspace 中：

To create an index on the column code in the table films and have the index reside in the tablespace indexspace:

CREATE INDEX code_idx ON films (code) TABLESPACE indexspace;

在点属性上创建一个 GiST 索引，以便我们能够有效地对转换函数的结果使用框运算符：

To create a GiST index on a point attribute so that we can efficiently use box operators on the result of the conversion function:

CREATE INDEX pointloc
    ON points USING gist (box(location,location));
SELECT * FROM points
    WHERE box(location,location) && '(0,0),(1,1)'::box;

创建索引而不锁定对表的写入：

To create an index without locking out writes to the table:

CREATE INDEX CONCURRENTLY sales_quantity_index ON sales_table (quantity);

Compatibility

CREATE INDEX 是一个 PostgreSQL 语言扩展。SQL 标准中没有对索引的规定。

CREATE INDEX is a PostgreSQL language extension. There are no provisions for indexes in the SQL standard.

See Also

ALTER INDEX 、 DROP INDEX 、 REINDEX 、 Section 28.4.4

ALTER INDEX, DROP INDEX, REINDEX, Section 28.4.4