Mastering PostgreSQL 12 - Third Edition

Spotting changes in runtime

When looking at a plan, there are always two questions that you have got to ask yourself:

• Is the runtime shown by the EXPLAIN ANALYZE clause justified for the given query?
• If the query is slow, where does the runtime jump?

In my case, the sequential scan is rated at 2.625 milliseconds. The sort is done after 7.199 milliseconds, so the sort takes roughly 4.5 milliseconds to complete and is therefore responsible for most of the runtime that's needed by the query.

Looking for jumps in the execution time of the query will reveal what's really going on. Depending on which type of operation will burn too much time, you have to act accordingly. Some general advice is not possible here because there are simply too many ...