51.49. pg_statistic
The catalog pg_statistic
stores statistical data about the contents of the database. Entries are created by ANALYZE and subsequently used by the query planner. Note that all the statistical data is inherently approximate, even assuming that it is up-to-date.
Normally there is one entry, with stainherit
= false
, for each table column that has been analyzed. If the table has inheritance children, a second entry with stainherit
= true
is also created. This row represents the column's statistics over the inheritance tree, i.e., statistics for the data you'd see with SELECT
column
FROM table
*, whereas the stainherit
= false
row represents the results of SELECT
column
FROM ONLY table
.
pg_statistic
also stores statistical data about the values of index expressions. These are described as if they were actual data columns; in particular, starelid
references the index. No entry is made for an ordinary non-expression index column, however, since it would be redundant with the entry for the underlying table column. Currently, entries for index expressions always have stainherit
= false
.
Since different kinds of statistics might be appropriate for different kinds of data, pg_statistic
is designed not to assume very much about what sort of statistics it stores. Only extremely general statistics (such as nullness) are given dedicated columns in pg_statistic
. Everything else is stored in “slots”, which are groups of associated columns whose content is identified by a code number in one of the slot's columns. For more information see src/include/catalog/pg_statistic.h
.
pg_statistic
should not be readable by the public, since even statistical information about a table's contents might be considered sensitive. (Example: minimum and maximum values of a salary column might be quite interesting.) pg_stats
is a publicly readable view on pg_statistic
that only exposes information about those tables that are readable by the current user.
Table 51.49. pg_statistic
Columns
pg_statistic
ColumnsLast updated