PG_STATISTIC Sistem Tablosu

Basic Statistics

Açıklaması şöyle

Statistics are data collected by Postgres used to inform its selection of query plans. Out of the box, Postgres samples the possible values for each column of each table to create histograms and a list of the most common values (among other things). These are used to estimate how many rows will result from applying some set of filters to a table.

For larger tables, the planner can’t keep track of every single value a column holds. Instead, it samples the values of each column and uses those to make estimations. We can tweak how much sampling Postgres does for each column on each table with

ALTER TABLE table ALTER column SET STATISTICS {-1 ..10000}

where -1 sets it to the default value of 100 (docs). This number sets how many buckets are used in the histogram and how many of the most common values are stored.

The downsides to increasing the statistics for a column are that more data must be stored in pg_statistic and running ANALYZE on the column's table takes longer.