Postgresql 中文操作指南

53.52. pg_statistic_ext #

目录 pg_statistic_ext 拥有扩展的计划员统计信息的定义。该目录中的每一行与使用 CREATE STATISTICS 创建的 statistics object 相对应。

The catalog pg_statistic_ext holds definitions of extended planner statistics. Each row in this catalog corresponds to a statistics object created with CREATE STATISTICS.

Table 53.52. pg_statistic_ext Columns

Table 53.52. pg_statistic_ext Columns

Column Type

Description

oid oid

Row identifier

stxrelid oid (references pg_class.oid)

Table containing the columns described by this object

stxname name

Name of the statistics object

stxnamespace oid (references pg_namespace.oid)

The OID of the namespace that contains this statistics object

stxowner oid (references pg_authid.oid)

Owner of the statistics object

stxstattarget int4

stxstattarget controls the level of detail of statistics accumulated for this statistics object by ANALYZE. A zero value indicates that no statistics should be collected. A negative value says to use the maximum of the statistics targets of the referenced columns, if set, or the system default statistics target. Positive values of stxstattarget determine the target number of “most common values” to collect.

stxkeys int2vector (references pg_attribute.attnum)

An array of attribute numbers, indicating which table columns are covered by this statistics object; for example a value of 1 3 would mean that the first and the third table columns are covered

stxkind char[]

An array containing codes for the enabled statistics kinds; valid values are: d for n-distinct statistics, f for functional dependency statistics, m for most common values (MCV) list statistics, and e for expression statistics

stxexprs pg_node_tree

Expression trees (in nodeToString() representation) for statistics object attributes that are not simple column references. This is a list with one element per expression. Null if all statistics object attributes are simple references.

pg_statistic_ext 条目在 CREATE STATISTICS 期间完全填充,但实际统计值不会在那时计算。后续的 ANALYZE 命令计算所需值,并在 pg_statistic_ext_data 目录中填充一个条目。

The pg_statistic_ext entry is filled in completely during CREATE STATISTICS, but the actual statistical values are not computed then. Subsequent ANALYZE commands compute the desired values and populate an entry in the pg_statistic_ext_data catalog.