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From: Erik Jones <erik@myemma.com>
To: Scott Marlowe <scott.marlowe@gmail.com>
Cc: Steve Midgley <public@misuse.org>
Cc: pgsql-sql-owner@postgresql.org
Cc: pgsql-sql@postgresql.org
Subject: Re: Re: How to keep at-most N rows per group? periodic DELETEs or constraints or..?
Date: Wed, 9 Jan 2008 14:17:39 -0600
Message-ID: <A92379CF-963E-4670-9E22-21225B927EF8@myemma.com> (raw)
In-Reply-To: <dcc563d10801091109kf80ce2dh97b8e4a548f5168f@mail.gmail.com>
References: <20080109152431.79AFF2E02F6@postgresql.org>
	<20080109182115.6E39C2E3239@postgresql.org>
	<dcc563d10801091109kf80ce2dh97b8e4a548f5168f@mail.gmail.com>


On Jan 9, 2008, at 1:09 PM, Scott Marlowe wrote:

> On Jan 9, 2008 12:20 PM, Steve Midgley <public@misuse.org> wrote:
>> This is kludgy but you would have some kind of random number test at
>> the start of the trigger - if it evals true once per every ten  
>> calls to
>> the trigger (say), you'd cut your delete statements execs by about  
>> 10x
>> and still periodically truncate every set of user rows fairly  
>> often. On
>> average you'd have ~55 rows per user, never less than 50 and a few
>> outliers with 60 or 70 rows before they get trimmed back down to 50..
>> Seems more reliable than a cron job, and solves your problem of an  
>> ever
>> growing table? You could adjust the random number test easily if you
>> change your mind of the balance of size of table vs. # of delete
>> statements down the road.
>
> And, if you always through a limit 50 on the end of queries that
> retrieve data, you could let it grow quite a bit more than 60 or 70...
> Say 200.  Then you could have it so that the random chopper function
> only gets kicked off every 100th or so time.

I like that idea.

Erik Jones

DBA | Emma®
erik@myemma.com
800.595.4401 or 615.292.5888
615.292.0777 (fax)

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