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Re: Improve compression speeds in pg_lzcompress.c

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Takeshi Yamamuro <yamamuro(dot)takeshi(at)lab(dot)ntt(dot)co(dot)jp>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Improve compression speeds in pg_lzcompress.c
Date: 2013-01-07 16:16:07
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Lists: pgsql-hackers
Takeshi Yamamuro <yamamuro(dot)takeshi(at)lab(dot)ntt(dot)co(dot)jp> writes:
> The attached is a patch to improve compression speeds with loss of
> compression ratios in backend/utils/adt/pg_lzcompress.c.

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.

Another thing to keep in mind is that the compression area in general
is a minefield of patents.  We're fairly confident that pg_lzcompress
as-is doesn't fall foul of any, but any significant change there would
probably require more research.

			regards, tom lane

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