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Re: Pg_upgrade speed for many tables

From: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Magnus Hagander <magnus(at)hagander(dot)net>
Subject: Re: Pg_upgrade speed for many tables
Date: 2012-11-05 23:15:30
Message-ID: CAMkU=1ys+=FVMeYy5JT7Z8hD3EkVMYcMw3Z7wvv+BgmFbcMxHQ@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Mon, Nov 5, 2012 at 12:14 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> writes:
>> Magnus reported that a customer with a million tables was finding
>> pg_upgrade slow.
>
> You sure there's not an O(N^2) issue in there somewhere?

There certainly will be before he gets to a million, but it probably
doesn't show up yet testing at 2000.

He will probably have to hack pg_dump, as discussed here:

http://archives.postgresql.org/pgsql-performance/2012-09/msg00003.php


>
>> I don't see anything unsafe about having pg_upgrade use
>> synchronous_commit=off.
>
> No objection, but this seems unlikely to be better than linear speedup,
> with a not-terribly-large constant factor.
>
> BTW, does pg_upgrade run pg_restore in --single-transaction mode?
> That would probably make synchronous_commit moot, at least for that
> step.

Doing that might make the sync problem better, but would make the N^2
problem worse if upgrading to <= 9.2 .

Cheers,

Jeff


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