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Re: synchronized scans for VACUUM

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Gregory Stark <stark(at)enterprisedb(dot)com>
Cc: "Jeff Davis" <pgsql(at)j-davis(dot)com>, "pgsql-hackers" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: synchronized scans for VACUUM
Date: 2008-06-01 13:57:42
Message-ID: 19398.1212328662@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Gregory Stark <stark(at)enterprisedb(dot)com> writes:
>> It will certainly not "solve" the problem.  What it will do is mean that
>> the breaks are further apart and longer, which seems to me to make the
>> conflict with syncscan behavior worse not better.

> How would it make them longer? They still have the same amount of i/o to do
> scanning the indexes. I suppose they would dirty more pages which might slow
> them down?

More tuples to delete = more writes (in WAL, if not immediately in the
index itself) = longer to complete the indexscan.  It's still cheaper
than doing multiple indexscans, of course, but my point is that the
index-fixing work gets concentrated.

			regards, tom lane

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