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Re: Postgresql 'eats' all mi data partition

From: Tomas Szepe <szepe(at)pinerecords(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>,Javier Carlos <fjcarlos(at)correo(dot)insp(dot)mx>, pgsql-bugs(at)postgresql(dot)org
Subject: Re: Postgresql 'eats' all mi data partition
Date: 2003-09-27 08:16:10
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-bugs
> [tgl(at)sss(dot)pgh(dot)pa(dot)us]
> > indexes:
> > stats_min_pkey primary key btree (ip, "start")
> > stats_min_start btree ("start")
> > stats_hr_pkey primary key btree (ip, "start")
> > stats_hr_start btree ("start")
> > ip is of type "inet" in all tables.
> > start is of type "timestamp without time zone" in all tables.
> Okay, so a pkey index entry will take 32 bytes counting overhead ...
> you've got about 10:1 bloat on the stats_min indexes and 2:1 in stats_hr.
> Definitely bad :-(

The only difference between the way stats_min and stats_hr are updated
stems from the fact that stats_min only holds records for the last 1440
minutes (because of its killer time granularity), whereas stats_hr
holds its data until we decide some of it is obsolete enough and
issue a "delete from" by hand.

Thus, the updates look like (pardon the pseudosql please):

	delete from stats_min where \
		[data is current minute but yesterday's, or even older,
		or from the future];
	[repeat for all ips]
		insert into stats_min [data for the current minute];
	[end repeat]

	[repeat for all ips]
		update stats_hr set [data += increment] where \
			[data is for current hour];
		[if no_of_rows_updated < 1]
			insert into stats_hr [current hour's first increment];
	[end repeat]

> I expect the bloat is coming from the fact that the interesting range of
> "start" changes over time.  7.4 should be able to recycle index space
> in that situation, but 7.3 and before can't.

OK, I'll definitely try 7.4 once I'm confident with it.

Thanks for your time,
Tomas Szepe <szepe(at)pinerecords(dot)com>

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Subject: Re: Postgresql 'eats' all mi data partition
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Subject: Re: wrong Bison version on INSTALL file

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