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Re: Very long deletion time on a 200 GB database

From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
To: Samuel Gendler <sgendler(at)ideasculptor(dot)com>
Cc: "Reuven M(dot) Lerner" <reuven(at)lerner(dot)co(dot)il>, sthomas(at)peak6(dot)com, pgsql-performance(at)postgresql(dot)org
Subject: Re: Very long deletion time on a 200 GB database
Date: 2012-02-27 21:28:33
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Lists: pgsql-performance
On Mon, Feb 27, 2012 at 2:13 PM, Samuel Gendler
<sgendler(at)ideasculptor(dot)com> wrote:
> On Mon, Feb 27, 2012 at 6:59 AM, Reuven M. Lerner <reuven(at)lerner(dot)co(dot)il>
> wrote:
>> So for now, we'll just try to DELETE faster than we INSERT, and combined
>> with autovacuum, I'm hoping that this crisis will be averted.  That said,
>> the current state of affairs with these machines is pretty fragile, and I
>> think that we might want to head off such problems in the future, rather
>> than be surprised by them.
> For the record, one very effective long term solution for doing this and
> continuing to be able to do this no matter how many rows have accumulated is
> to partition the data tables over time so that you can just drop older
> partitions.  It does require code changes since relying on a trigger on the
> parent table to distribute the inserts to the correct partition is much
> slower than simply modifying your code to insert/copy into the correct
> partition directly.  But it is well worth doing if you are accumulating
> large volumes of data.  You can even leave old partitions around if you
> don't need the disk space, since well-constructed queries will simply ignore
> their existence, anyway, if you are only ever going back 30 days or less.
>  Indexes are on individual partitions, so you needn't worry about indexes
> getting too large, either.

If they're only inserting ~1 or 2G a day, a trigger is likely plenty
fast.  I've had stats dbs that grew up 10s or 20s of gigs a day and
the triggers were never a performance problem there.

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