Re: Statistics Import and Export

From: Nathan Bossart <nathandbossart(at)gmail(dot)com>
To: Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
Cc: Jeff Davis <pgsql(at)j-davis(dot)com>, Robert Treat <rob(at)xzilla(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Michael Paquier <michael(at)paquier(dot)xyz>, jian he <jian(dot)universality(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, Magnus Hagander <magnus(at)hagander(dot)net>, Stephen Frost <sfrost(at)snowman(dot)net>, Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, Peter Smith <smithpb2250(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, alvherre(at)alvh(dot)no-ip(dot)org
Subject: Re: Statistics Import and Export
Date: 2025-03-18 01:01:48
Message-ID: Z9jF_D472ec1itOu@nathan
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On Mon, Mar 17, 2025 at 07:24:46PM -0400, Corey Huinker wrote:
> On Mon, Mar 17, 2025 at 10:24 AM Nathan Bossart <nathandbossart(at)gmail(dot)com>
> wrote:
>> I'm assuming that writing a completely different TOC on the second pass
>> would corrupt the dump file. Perhaps we could teach it to skip stats
>> entries on the second pass or something, but I'm not too wild about adding
>> to the list of invasive changes we're making last-minute for v18.
>
> I'm confused, are they needed in both places?

AFAICT yes. The second pass rewrites the TOC to udpate the data offset
information. If we wrote a different TOC the second time around, then the
dump file would be broken, right?

/*
* If possible, re-write the TOC in order to update the data offset
* information. This is not essential, as pg_restore can cope in most
* cases without it; but it can make pg_restore significantly faster
* in some situations (especially parallel restore).
*/
if (ctx->hasSeek &&
fseeko(AH->FH, tpos, SEEK_SET) == 0)
WriteToc(AH);

--
nathan

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