An Index Must Serve a Real Query

Sun, 01 Oct 2017 00:00:00 +0000

A production query needed a small page of recent records requiring operational attention. The table already had an index which looked relevant. The measured scan still discarded 84,003 historical index entries and recorded 122,936 shared-buffer reads before finding 83 eligible rows.

The missing index was not “an index on the table.” It was an index for this query:

one tenant
active records with zero price
created during the last three months
newest creation time first
stable identifier as the tie-breaker
first page only

Indexing starts with the access path, not with a list of columns which sound important.

Postgresql on Brian Faust

An Index Must Serve a Real Query