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Re: Improve compression speeds in pg_lzcompress.c

From: Andrew Dunstan <andrew(at)dunslane(dot)net>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Takeshi Yamamuro <yamamuro(dot)takeshi(at)lab(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Improve compression speeds in pg_lzcompress.c
Date: 2013-01-07 21:44:50
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Lists: pgsql-hackers
On 01/07/2013 04:19 PM, Tom Lane wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Mon, Jan 7, 2013 at 11:16 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> Why would that be a good tradeoff to make?  Larger stored values require
>>> more I/O, which is likely to swamp any CPU savings in the compression
>>> step.  Not to mention that a value once written may be read many times,
>>> so the extra I/O cost could be multiplied many times over later on.
>> I agree with this analysis, but I note that the test results show it
>> actually improving things along both parameters.
> Hm ... one of us is reading those results backwards, then.

I just went back and looked. Unless I'm misreading it he has about a 2.5 
times speed improvement but about a 20% worse compression result.

What would be interesting would be to see if the knobs he's tweaked 
could be tweaked a bit more to give us substantial speedup without 
significant space degradation.



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