Postgres allows you to index the result of that function so that searches become as efficient as searching by raw data values. Expression IndexesĮxpression indexes are useful for queries that match on some function or modification of your data. This index will remain fairly small, and can also be used along other indexes on the more complex queries that may require it. You may want to create an index like so: CREATE INDEX articles_flagged_created_at_index ON articles(created_at) WHERE flagged IS TRUE You then process flagged comments in batches. A smaller index takes less storage, is easier to maintain, and is faster to scan.įor example, suppose you allow users to flag comments on your site, which in turn sets the flagged boolean to true. The idea is to increase the efficiency of the index by reducing its size.
Partial IndexesĪ partial index covers just a subset of a table’s data. When this happens, a sequential scan is actually most likely much faster than an index scan, so the query planner has in fact correctly judged that the cost of performing the query that way is lower. So, for example, it might be correct for the query planner to use an index for the query select * from foo where bar = 1, and yet not use one for the query select * from foo where bar = 2, if there happened to be far more rows with “bar” values of 2. The number of rows retrieved from the table may vary based on the particular constant values the query retrieves. It’s okay if the same query uses an index scan on some occasions but not others. Most of the time, the planner chooses correctly, even if it isn’t obvious why. There are many reasons why the Postgres planner may choose to not use an index. For examples of GIN and GiST index usage, refer to the contrib packages.
PGADMIN 4 QUERY FORMAT HOW TO
This article is about how to get the most out of default B-Tree indexes. They are used to index the geometric data types, as well as full-text search.
In Postgres 10 and above, hash indexes are now write-ahead logged and replicated to followers.
Virtually all databases will have some B-tree indexes.