Re: Default gucs for EXPLAIN
От | Fabien COELHO |
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Тема | Re: Default gucs for EXPLAIN |
Дата | |
Msg-id | alpine.DEB.2.22.394.2005240910330.463947@pseudo обсуждение исходный текст |
Ответ на | Re: Default gucs for EXPLAIN (Vik Fearing <vik@postgresfriends.org>) |
Ответы |
Re: Default gucs for EXPLAIN
Re: Default gucs for EXPLAIN |
Список | pgsql-hackers |
Bonjour Vik, >> Do we really want default_explain_analyze ? >> It sounds like bad news that EXPLAIN DELETE might or might not remove rows >> depending on the state of a variable. > > I have had sessions where not using ANALYZE was the exception, not the > rule. I would much prefer to type EXPLAIN (ANALYZE OFF) in those cases. I concur with Justin that having EXPLAIN DELETE/UPDATE actually executing the query can be too much a bit of a surprise for a user attempting it. A typical scenario would be "this DELETE/UPDATE query is too slow", admin connects to production and try safe EXPLAIN on some random sample, and get bitten because the default was changed. A way out could be having 3 states for analyse (off, read-only, on) which would block updates/deletes by making the transaction/operation read-only to prevent side effects, unless explicitely asked for? I'm not sure if this can be easily implemented, though. Or maybe run the query in a separate transaction which is then coldly rollbacked? Hmmm, I'm not really convincing myself on this one… The safe option seems not allowing to change ANALYZE option default. While testing the issue, I'm surprised at the syntax: EXPLAIN [ ( option [, ...] ) ] statement EXPLAIN [ ANALYZE ] [ VERBOSE ] statement Why not allowing the following: EXPLAIN [ ANALYZE ] [ VERBOSE ] [ ( option [, ...] ) ] statement -- Fabien.
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