alt Hacker News>There are reasons for that, it's useful in a very narrow set of situations.
So narrow its enabled by default for all statements from the "big boy" commercial RDBMS's...
https://www.ibm.com/docs/en/i/7.4.0?topic=overview-plan-cach...
https://docs.oracle.com/en/database/oracle/oracle-database/1...
https://learn.microsoft.com/en-us/sql/relational-databases/p...
https://help.sap.com/docs/SAP_HANA_PLATFORM/6b94445c94ae495c...
>Postgres cached plans exist for the same reason.
Postgresql doesn't cache plans unless the client explicitly sends commands to do so. Applications cannot take advantage of this unless they keep connections open and reuse them in a pool and they must mange this themselves. The plan has to be planned for every separate connection/process rather than a single cached planed increasing server memory costs which are plan cache size X number of connections.
It has no "reason" to cache plans the client must do this using its "reasons".
>If you're claiming Oracle and MSSQL do _much_ better in this area - that's what I call unsubstantiated.
You are making all sorts of claims without nary a link to back it up. Are you suggestion PG does better than MSSQL, Oracle and DB2 in planning while be constrained to replan on every single statement? The PG planner is specifically kept simple so that it is fast at its job, not thorough or it would adversely effect execution time more than it already does, this is well documented and always a concern when new features are proposed for it.
>From what you write further it's pretty clear you don't have a lot of understanding what happens under the hood.
Sticks and stones, is that all you have how about something substantial.
> And no, prepared statements are not what you read in Wikipedia. Not in all databases anyway.
Ok Mr. Unsubstantiated are we talking about PG or not? What does one use prepared statements for in PG hmmm, you know the thing you call the PG plan cache? How about something besides your claim that prepared statements are not in fact plan caches? Are you talking about completely different DB systems? How about you substantiate that?
https://www.postgresql.org/docs/current/runtime-config-query...
and then
https://www.postgresql.org/docs/current/sql-prepare.html
Read carefully about "plan_cache_mode" and how it works (and its default settings). Sorry, that's my last message in this thread, and I'm still here just for educational purposes, because what you're talking about is in fact a common misconception. If you read it carefully, you'll see that generic plans do not require any "explicit commands", Postgres executes a query 5 times in custom mode, then tries a generic one, if it worked (not much worse than an average of 5 custom plans), the plan is cached. You can turn it off though. And I'd recommend to turn it off for most cases, because it's a pretty bad heuristics. Nevertheless, for some (pretty narrow set of) cases it's useful.
So, Mr Big Boy, now we can get to what a prepared statement in Postgres is. Prepared statements are cached in a session, but if that statement was cached in custom mode, it won't contain a plan. When Postgres receives a prepared statement in custom mode, it will just skip parsing, that's it. The query will still be planned, because custom plans rely on input parameters. If we run it in generic mode, then the plan is cached.