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Re: Performance on inserts

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Alfred Perlstein <bright(at)wintelcom(dot)net>
Cc: Jules Bean <jules(at)jellybean(dot)co(dot)uk>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Performance on inserts
Date: 2000-08-25 18:25:37
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Lists: pgsql-hackers
Alfred Perlstein <bright(at)wintelcom(dot)net> writes:
> I'm unsure if it's possible, but somehow storing the last place one
> 'gave up' and decided to split the page could offer a useful next-start
> for the next insert.

I think that that would create problems with concurrency --- the
Lehman-Yao btree algorithm is designed around the assumption that
writers only move right and never want to go back left to change
a prior page.  So once we've moved right we don't get to go back to
the start of the chain of duplicates.

> For some reason it looks like your algorithm might cause
> problems because it plain gives up after 10 pages?

"Give up" just means "stop looking for already-existing free space,
and make some the hard way".  The steady-state average space utilization
of this way would be somewhat worse than the existing code, probably,
but I don't see that as a big problem.

			regards, tom lane

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