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Re: Proposed patch to change TOAST compression strategy

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Gregory Stark <stark(at)enterprisedb(dot)com>
Cc: pgsql-patches(at)postgresql(dot)org, "Jan Wieck" <JanWieck(at)Yahoo(dot)com>
Subject: Re: Proposed patch to change TOAST compression strategy
Date: 2008-03-07 23:23:12
Message-ID: 8565.1204932192@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-patches
Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>> * Adds an early-failure path to the compressor as suggested by Jan:
>> if it's been unable to find even one compressible substring in the
>> first 1KB (parameterizable), assume we're looking at incompressible
>> input and give up.  (There are various ways this could be done, but
>> this way seems to add the least overhead to the compressor's inner
>> loop.)

> I'm not sure how to test the rest of it, but this bit seems testable. I fear
> this may be too conservative. Even nigh incompressible data will find a few
> backreferences.
> I'll try some tests and see.

On the strength of Teodor's favorable test, I went ahead and applied
this patch as-is.  We can certainly tweak the compressor logic again
if you can show an improvement by changing it further.

			regards, tom lane

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