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Re: Experimental patch for inter-page delay in VACUUM

From: Ang Chin Han <angch(at)bytecraft(dot)com(dot)my>
To: Christopher Browne <cbbrowne(at)acm(dot)org>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Experimental patch for inter-page delay in VACUUM
Date: 2003-11-04 04:07:55
Message-ID: 3FA7261B.1060005@bytecraft.com.my (view raw or flat)
Thread:
Lists: pgsql-hackers
Christopher Browne wrote:
> Centuries ago, Nostradamus foresaw when "Stephen" <jleelim(at)xxxxxxx(dot)com> would write:
> 
>>As it turns out. With vacuum_page_delay = 0, VACUUM took 1m20s (80s)
>>to complete, with vacuum_page_delay = 1 and vacuum_page_delay = 10,
>>both VACUUMs completed in 18m3s (1080 sec). A factor of 13 times! 
>>This is for a single 350 MB table.
> 
> 
> While it is unfortunate that the minimum quanta seems to commonly be
> 10ms, it doesn't strike me as an enormous difficulty from a practical
> perspective.

If we can't lower the minimum quanta, we could always vacuum 2 pages 
before sleeping 10ms, effectively sleeping 5ms.

Say,
vacuum_page_per_delay = 2
vacuum_time_per_delay = 10

What would be interesting would be pg_autovacuum changing these values 
per table, depending on current I/O load.

Hmmm. Looks like there's a lot of interesting things pg_autovacuum can do:
1. When on low I/O load, running multiple vacuums on different, smaller 
tables on full speed, careful to note that these vacuums will increase 
the I/O load as well.
2. When on high I/O load, vacuum big, busy tables slowly.

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Subject: Re: Experimental patch for inter-page delay in VACUUM
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