Re: Preliminary patch for on-the-fly relpages/reltuples

From: Markus Bertheau <twanger(at)bluetwanger(dot)de>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-patches(at)postgresql(dot)org
Subject: Re: Preliminary patch for on-the-fly relpages/reltuples
Date: 2004-12-06 10:14:41
Message-ID: 1102328081.3382.1.camel@fc3
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В Пнд, 29/11/2004 в 19:14 -0500, Tom Lane пишет:
> + /*
> + * lazy_update_relstats - update pg_class statistics for a table or index
> + *
> + * We always want to set relpages to an accurate value. However, for lazy
> + * VACUUM it seems best to set reltuples to the average of the number of
> + * rows before vacuuming and the number after vacuuming, rather than just
> + * using the number after vacuuming. This will result in the best average
> + * performance in a steady-state situation where VACUUMs are performed
> + * regularly on a table of roughly constant size, assuming that the physical
> + * number of pages in the table stays about the same throughout. (Note that
> + * we do not apply the same logic to VACUUM FULL, because it repacks the table
> + * and thereby boosts the tuple density.)
> + */
> + static void
> + lazy_update_relstats(Relation rel, BlockNumber num_pages,
> + double num_tuples, double tuples_removed,
> + bool hasindex)
> + {
> + num_tuples = ceil(num_tuples + tuples_removed * 0.5);

Not understanding a thing about the PG source code, and judging from the
variable names, wouldn't you want ceil(num_tuples + (num_tuples -
tuples_removed) * 0.5) instead?

> + vac_update_relstats(RelationGetRelid(rel), num_pages, num_tuples,
> + hasindex);
> }

--
Markus Bertheau <twanger(at)bluetwanger(dot)de>

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