| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Jeff Davis <pgsql(at)j-davis(dot)com> |
| Cc: | Andrei Lepikhov <lepihov(at)gmail(dot)com>, Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Organize working memory under per-PlanState context |
| Date: | 2025-08-20 17:07:30 |
| Message-ID: | 1182219.1755709650@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> On Wed, 2025-08-20 at 09:22 +0200, Andrei Lepikhov wrote:
>> Building a hash table repeatedly may be pretty costly, no?
> We can check the eflags for EXEC_FLAG_REWIND. That might not be the
> only condition we need to check, but we should know at plan time
> whether a subtree might be executed more than once.
Side note: EXEC_FLAG_REWIND is defined as "you should be prepared
to handle REWIND efficiently". Not as "if this is off, you are
guaranteed not to see a REWIND". I'm not sure that this affects
what Jeff wants to do, but let's not be fuzzy about what information
is available at execution time.
regards, tom lane
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