Re: BUG: pg_stat_statements query normalization issues with combined queries

From: Craig Ringer <craig(dot)ringer(at)2ndquadrant(dot)com>
To: Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: BUG: pg_stat_statements query normalization issues with combined queries
Date: 2017-01-13 14:08:29
Message-ID: CAMsr+YHReea2vJi6PUnXpAiEq-EjJ1vMDaxNE3c2es0UUXkEgg@mail.gmail.com
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On 13 Jan. 2017 16:35, "Kyotaro HORIGUCHI" <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
wrote:

Hello,

At Thu, 12 Jan 2017 20:08:54 +0100 (CET), Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
wrote in <alpine(dot)DEB(dot)2(dot)20(dot)1701122004190(dot)3788(at)lancre>
>
> About having a pointer to the initial string from RawStmt, Query &
> PlannedStmt:
>
> > I remembered one reason why we haven't done this: it's unclear how
> > we'd handle copying if we do it. If, say, Query contains a "char *"
> > pointer then you'd expect copyObject() to pstrdup that string, [...,
> > So] We'd need to work out a way of managing multiple Queries carrying
> > references to the same source string, and it's not clear how to do
> > that reasonably.
>
> For me it would be shared, but then it may break some memory
> management hypothesis downstream.

+1 to they have a pointer to the shared query string. But doing
that without some measure like reference counting seems
difficult..

Sounds like it'd be better as a separate change so as not to block this one.

I really like what you have done Tom, though I'm about to travel so I
haven't read it in full detail. Like Fabien I would've been certain that
it'd be rejected if I tried it, but I sure am glad you did it.

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