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Re: Admission Control

From: Martijn van Oosterhout <kleptog(at)svana(dot)org>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>,pgsql-hackers(at)postgresql(dot)org
Subject: Re: Admission Control
Date: 2010-06-26 15:59:29
Message-ID: 20100626155929.GC4512@svana.org (view raw or flat)
Thread:
Lists: pgsql-hackers
On Sat, Jun 26, 2010 at 11:37:16AM -0400, Robert Haas wrote:
> On Sat, Jun 26, 2010 at 11:03 AM, Martijn van Oosterhout
> > (It doesn't help in situations where you can't accurately predict
> > memory usage, like hash tables.)
> 
> Not sure what you mean by this part.  We already predict how much
> memory a hash table will use.

By this I mean where the memory usage of the HashAggregate depends on
how many groups there are, and it's sometimes very difficult to predict
that beforehand. Though maybe that got fixed.

Another issue is cached plans. Say there is increased memory pressure,
at what point do you start replanning existing plans?

While this does have the advantage of being relatively simple to
implement, I think it would be a bitch to tune...

Have a nice day,
-- 
Martijn van Oosterhout   <kleptog(at)svana(dot)org>   http://svana.org/kleptog/
> Patriotism is when love of your own people comes first; nationalism,
> when hate for people other than your own comes first. 
>                                       - Charles de Gaulle

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