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  3. Improving Query Performance in PostgreSQL

Exercise

Exploring pg_tables

In order to make a query plan, the query planner needs basic information like table names, column names, and the number of rows of each table or view. Without this information, the planner would not know how many rows to search to find a specific columns used in filter conditions. It would not know if it can use an index search.

This type of metadata is stored in the pg_tables schema. Specifically, the planner uses pg_class and pg_stats. Take a look to see what kind of information these objects contain.

Instructions 1/2

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  • 1

    First, find all the columns in pg_class. Then select the column that indicates if the daily_aqi table has an index.

  • 2

    Use pg_stats to find column level statistics. Filter the daily_aqi table to category.