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Re: Higher TOAST compression.

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Laurent Laborde" <kerdezixe(at)gmail(dot)com>
Cc: <jd(at)commandprompt(dot)com>, "PostgreSQL-development" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Higher TOAST compression.
Date: 2009-07-17 20:40:23
Message-ID: 4A609B670200002500028947@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-hackers
Laurent Laborde <kerdezixe(at)gmail(dot)com> wrote: 
> Kevin Grittner<Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:
 
>> How about two new ALTER TABLE actions:
>>
>>   ALTER [ COLUMN ] column SET COMPRESSION_THRESHOLD integer
>>   ALTER [ COLUMN ] column SET EXTERNAL_THRESHOLD integer
 
>> Laurent, would something like this address your needs?
 
> Certainly !
> We already alter storage type on some column, adding some more won't
> be a problem. :)
> 
> But... on which version are you planning to do that ?
 
The patch, if there's consensus that it's a good idea, would be for
8.5.  Since it is new functionality, there wouldn't be a back-port to
prior releases.  Of course, I wouldn't be starting to work on such a
patch until after our current code commit phase, which ends August
15th.
 
> We stay on Pg 8.3 until the slony developpers find a better upgrade 
> solution.
> 
> The proposed solution sound really good to me.
> But, for now, if i could have a simple patch for 8.3 (eg: changing a
> #define in the source code), i'd be very happy :)
> 
> Is it ok to just change TOAST_TUPLES_PER_PAGE ?
 
The thing that worries me about that is that it would tend to force
more data to be stored out-of-line, which might *increase* your I/O;
since the whole point of this exercise is to try to *decrease* it,
that seems pretty iffy.  However, once we get to the end of code
commit, I might be able to give you a little one-off patch that would
be more aggressive about compression without affecting out-of-line
storage.  Hard-coded, like what you're talking about, but with a
little more finesse.
 
-Kevin

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