From: Tom Lane <tgl@sss.pgh.pa.us>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: pgsql-committers@lists.postgresql.org, Konstantin Knizhnik <k.knizhnik@postgrespro.ru>
Subject: Re: pgsql: Allow HOT updates for some expression indexes
Date: Tue, 27 Mar 2018 17:26:26 -0400
Message-ID: <31021.1522185986@sss.pgh.pa.us> (raw)
In-Reply-To: <11787.1522184835@sss.pgh.pa.us>
References: <E1f0tqf-0007Vs-JZ@gemulon.postgresql.org>
<CANP8+jLd4USe=yuN77NVQOyijO9Wn4DFNt+iLr74sBVuCSBnsQ@mail.gmail.com>
<CANP8+jKLMvyHqy7PTn-HBEvSh3-dH+OOEiwJJYV2XMkF2UshtQ@mail.gmail.com>
<11787.1522184835@sss.pgh.pa.us>
I wrote:
> The test script appears to imagine that pgstats outputs update
> instantaneously.
Oh, wait, it's looking at pg_stat_xact, which is the *local*, unsent
stats information. So your problem is actually the reverse of that:
if the test runs too slowly, it fails, because at some point the
unsent stats information will get flushed out to the collector and
disappear from the pg_stat_xact view.
You could probably make this more reliable by wrapping each test
stanza in a transaction, ie instead of
create table keyvalue ...;
... do something to table ...
select pg_stat_get_xact_tuples_hot_updated('keyvalue'::regclass);
drop table keyvalue;
do
begin;
create table keyvalue ...;
... do something to table ...
select pg_stat_get_xact_tuples_hot_updated('keyvalue'::regclass);
rollback;
(no need for a DROP if you're rolling it all back)
regards, tom lane
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To: pgsql-committers@postgresql.org
Cc: tgl@sss.pgh.pa.us, simon@2ndquadrant.com, k.knizhnik@postgrespro.ru
Subject: Re: pgsql: Allow HOT updates for some expression indexes
In-Reply-To: <31021.1522185986@sss.pgh.pa.us>
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