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#AMAZON AWS POSTGRESQL 10 HOW TO#

These statistics collect information about count accesses to tables and indexes in both disk block and individual row terms. These types of stats are collected by the statistics collector. In addition to data distribution and extended statistics, there are monitoring statistics as well. Seq Scan on ext_stats (cost=47.65 rows=1017 width=8) (actual time=0.076.615.219 rows=1000 loops=1)Īs you see, estimated rows (1,017) is very close to the actual number.Īll the queries with filters on both columns will have much better estimates using extended statistics.

Postgres=> explain analyze select * from ext_stats where a=1 and b=0 INFO: "ext_stats": scanned 30000 of 44248 pages, containing 6779952 live rows and 0 dead rows 30000 rows in sample, 9999977 estimated total rows Postgres=> create statistics s_ext_depend(dependencies) on a,b from ext_stats

Without extended statistics, selecting one column looks fine with the estimated rows as 999, which is almost the same as actual rows which is 1000:.

You can see the distinct values for column a as 1000 and b as 100. Postgres=> SELECT * FROM pg_stats WHERE tablename ='test_stats'

Create a table and insert some dummy data:.

The following is an example of how you can generate and see these stats: They’re collected when we run ANALYZE or when analyze is triggered by autovacuum, and are stored in the pg_statistic system catalog (whose public readable view is pg_stats). They provide information about the most common values in each column in a relation, average width of the column, number of distinct values in the column, and more. These statistics are related to the data distribution for each relation. We explain each type in more detail in this post. The following types of statistics are collected and available in PostgreSQL: This applies to both Amazon RDS for PostgreSQL and Aurora PostgreSQL.

#AMAZON AWS POSTGRESQL 10 HOW TO#

The purpose of this post is to explain the types of statistics in PostgreSQL and how to read and understand them.

The query planner uses the statistical data to generate efficient run plans for queries. AWS provides two managed PostgreSQL options: Amazon Relational Database Service (Amazon RDS) for PostgreSQL and Amazon Aurora PostgreSQL-Compatible Edition.ĭatabase statistics play a key role in improving the performance of the database. PostgreSQL has become the preferred open-source relational database for many enterprise developers and startups, and powers leading business and mobile applications.