| From: | Marti Raudsepp <marti(at)juffo(dot)org> |
|---|---|
| To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Josh Berkus <josh(at)agliodbs(dot)com> |
| Subject: | Re: [PATCH] Caching for stable expressions with constant arguments v3 |
| Date: | 2011-12-07 21:58:23 |
| Message-ID: | CABRT9RDJiQKcbbYWzykVFiacDv9nBxzBJGSDLPMqVe5ohiSi2g@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Dec 7, 2011 at 00:29, Marti Raudsepp <marti(at)juffo(dot)org> wrote:
> ExecInitExpr enables the cache when its 'PlanState *parent' attribute
> isn't NULL
[...]
> On the other hand, a few places lose caching support this way since
> they don't go through the planner:
> * Column defaults in a COPY FROM operation. Common use case is
> 'timestamp default now()'
> This might be a significant loss in some data-loading scenarios.
> * ALTER TABLE t ALTER col TYPE x USING some_expr(); No big loss here.
Let me rephrase that as a question: Does it seem worthwhile to add a
new argument to ExecInitExpr to handle those two cases? Does relying
on the PlanState argument being NULL seem like a bad idea for any
reason?
PS: I forgot to mention that 2 test cases covering the two above query
types are deliberately left failing in the v4-wip patch.
Regards,
Marti
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