pg_stat_statements: everything it tells you

If not first, pg_stat_statements is one of the most used extensions in the PostgreSQL ecosystem. It ships in contrib and costs almost nothing to use. Most of us turn to it to answer the question: what is the database actually doing? It's genuinely useful. You can use it to get a snapshot of what happened in a given timeframe, and make a faster decision about what to fix. Coming from other database engines, you might reach for it expecting something a bit more, a query store. The built-in feature that keeps normalized queries and their plan history. Except pg_stat_statements is not this. This article is going to deep dive into what the extension really provides. Because once you lean on it, you might start noticing the rough edges. The gap comes from what "a query store" might come with and what it actually tells you. The very same query might show up in many separate rows. Discrepancies between what your monitoring says and what mean_exec_time shows. Missing queries. Numbers that…