postgresql - 在 Postgres pg_stat_statements 中，最大时间和平均时间之间的巨大差异

Question

在 Postgres 14 中，为什么和pg_stat_statements之间存在巨大的时差？max_exec_timemean_exec_time

能否请你帮忙？

Answer 1

That means that the execution time varies considerably. To see if that is just a single outlier or a regular occurrence, see if stddev_exec_time is high or not.

It can mean several things:

• Perhaps execution sometimes took long because the statement was stuck behind a lock. If that is a rare occurrence, it may me the odd ALTER TABLE statement.

• Perhaps the execution time varies depending on a query parameter. It may be fast for rare values and slow for frequent ones. Test with different parameters!

• Perhaps execution time varies depending on how much of the data happens to be cached in RAM. Look at a high "buffers" footprint in the EXPLAIN (ANALYZE, BUFFERS) output.