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List:       postgresql-general
Subject:    Re: [HACKERS] Index vacuum improvements
From:       Tom Lane <tgl () sss ! pgh ! pa ! us>
Date:       2006-03-31 16:50:17
Message-ID: 9780.1143823817 () sss ! pgh ! pa ! us
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Heikki Linnakangas <hlinnaka@iki.fi> writes:
> On Wed, 29 Mar 2006, Tom Lane wrote:
>> That loses the ability to reflect tuple deadness back into LP_DELETE
>> flags, no?

> At first glance, it doesn't look so hard. index_getmulti could mark 
> those tids that are dead, and btgetmulti would rescan the index page and 
> set LP_DELETE on all tuples that are still there.

> We don't have to care about splits; if the index tuple is no longer where 
> it used to be, just ignore it. Right, no?

True --- as long as there's even a reasonable probability of the tuple
getting marked, we'll get the performance benefit.  I don't see a way to
make it work for bitmap indexscans though --- by the time we visit the
heap, the index has long since forgotten where those index entries were.

I think this may be worth doing even disregarding any possible vacuum
speedup, simply because it'll reduce the number of index page lock/unlock
cycles needed during a regular indexscan.

			regards, tom lane

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