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Re: autovacuum not prioritising for-wraparound tables

From: Kevin Grittner <kgrittn(at)ymail(dot)com>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: Andres Freund <andres(at)2ndquadrant(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: autovacuum not prioritising for-wraparound tables
Date: 2013-01-30 18:31:50
Message-ID: 1359570710.31134.YahooMailNeo@web162905.mail.bf1.yahoo.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> Kevin Grittner <kgrittn(at)ymail(dot)com> wrote:

>> So reducing vacuum_freeze_min_age not only helps minimize the
>> writes that are needed when autovacuum needs to scan the entire
>> heap,
>
> How does it do that? If the tuple doesn't need to frozen now
> because it was already frozen, that just means the write happened
> at a different time but it still happened.

There's a lot to be said for nibbling away at it during VM
autovacuum runs versus doing it in big chunks in heap-scan runs,
particularly if your BBU cache can absorb up to a certain amout
with no real pain, but causes major pain if the write cache fills.

-Kevin


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Subject: Re: Hm, table constraints aren't so unique as all that
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