From: | Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com> |
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To: | Andrey Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru> |
Cc: | Justin Pryzby <pryzby(at)telsasoft(dot)com>, Zhihong Yu <zyu(at)yugabyte(dot)com>, Amit Langote <amitlangote09(at)gmail(dot)com>, tanghy(dot)fnst(at)fujitsu(dot)com, Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, houzj(dot)fnst(at)fujitsu(dot)com |
Subject: | Re: Fast COPY FROM based on batch insert |
Date: | 2022-08-01 04:00:13 |
Message-ID: | CAPmGK16UGGoTFrPe9gq=tLL8qzzTwzHpAkvg8p4RAyp7eL_EWA@mail.gmail.com |
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On Wed, Jul 27, 2022 at 2:42 PM Andrey Lepikhov
<a(dot)lepikhov(at)postgrespro(dot)ru> wrote:
> On 7/22/22 13:14, Etsuro Fujita wrote:
> > On Fri, Jul 22, 2022 at 3:39 PM Andrey Lepikhov
> > <a(dot)lepikhov(at)postgrespro(dot)ru> wrote:
> >> Analyzing multi-level heterogeneous partitioned configurations I
> >> realized, that single write into a partition with a trigger will flush
> >> buffers for all other partitions of the parent table even if the parent
> >> haven't any triggers.
> >> It relates to the code:
> >> else if (insertMethod == CIM_MULTI_CONDITIONAL &&
> >> !CopyMultiInsertInfoIsEmpty(&multiInsertInfo))
> >> {
> >> /*
> >> * Flush pending inserts if this partition can't use
> >> * batching, so rows are visible to triggers etc.
> >> */
> >> CopyMultiInsertInfoFlush(&multiInsertInfo, resultRelInfo);
> >> }
> >>
> >> Why such cascade flush is really necessary, especially for BEFORE and
> >> INSTEAD OF triggers?
> >
> > BEFORE triggers on the chosen partition might query the parent table,
> > not just the partition, so I think we need to do this so that such
> > triggers can see all the rows that have been inserted into the parent
> > table until then.
> if you'll excuse me, I will add one more argument.
> It wasn't clear, so I've made an experiment: result of a SELECT in an
> INSERT trigger function shows only data, existed in the parent table
> before the start of COPY.
Is the trigger function declared VOLATILE? If so, the trigger should
see modifications to the parent table as well. See:
https://www.postgresql.org/docs/15/trigger-datachanges.html
Best regards,
Etsuro Fujita
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