From: | jian he <jian(dot)universality(at)gmail(dot)com> |
---|---|
To: | Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, zwj <sxzwj(at)vip(dot)qq(dot)com>, pgsql-hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
Subject: | Re: bug report: some issues about pg_15_stable(8fa4a1ac61189efffb8b851ee77e1bc87360c445) |
Date: | 2024-02-29 03:04:35 |
Message-ID: | CACJufxFfbDhKiNHs8+pnZcZMtOHiANcXzV=JG_Qf=bhi6=vL7w@mail.gmail.com |
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On Wed, Feb 28, 2024 at 8:11 PM Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com> wrote:
>
> On Wed, 28 Feb 2024 at 09:16, jian he <jian(dot)universality(at)gmail(dot)com> wrote:
> >
> > + oldcontext = MemoryContextSwitchTo(estate->es_query_cxt);
> > +
> > + node->as_epq_tupdesc = lookup_rowtype_tupdesc_copy(tupType, tupTypmod);
> > +
> > + ExecAssignExprContext(estate, &node->ps);
> > +
> > + node->ps.ps_ProjInfo =
> > + ExecBuildProjectionInfo(castNode(Append, node->ps.plan)->epq_targetlist,
> > +
> > EvalPlanQualStart, EvalPlanQualNext will switch the memory context to
> > es_query_cxt.
> > so the memory context switch here is not necessary?
> >
>
> Yes it is necessary. The EvalPlanQual mechanism switches to the
> epqstate->recheckestate->es_query_cxt memory context, which is not the
> same as the main query's estate->es_query_cxt (they're different
> executor states). Most stuff allocated under EvalPlanQual() is
> intended to be short-lived (just for the duration of that specific EPQ
> check), whereas this stuff (the TupleDesc and Projection) is intended
> to last for the duration of the main query, so that it can be reused
> in later EPQ checks.
>
sorry for the noise. I understand it now.
Another small question:
for the Append case, we can set/initialize it at create_append_plan,
all other elements are initialized there,
why we set it at set_append_references.
just wondering.
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