Re: AW: Re: TODO list - Mailing list pgsql-hackers

From Tom Lane
Subject Re: AW: Re: TODO list
Date
Msg-id 21533.986490337@sss.pgh.pa.us
Whole thread Raw
In response to AW: Re: TODO list  (Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>)
List pgsql-hackers
Zeugswetter Andreas SB  <ZeugswetterA@wien.spardat.at> writes:
> Has anybody done performance and reliability tests with CRC64 ? 
> I think it must be a CPU eater. It looks a lot more complex than a CRC32.

On my box (PA-RISC) the inner loop is about 14 cycles/byte, vs. about
7 cycles/byte for CRC32.  On almost any machine, either one will be
negligible in comparison to the cost of disk I/O.

> Since we need to guard a maximum of 32k bytes for pg pages I would -
> if at all - consider to use a 32bit adler instead of a CRC, since that
> is a lot cheaper to calculate.

You are several months too late to re-open that argument.  It's done and
it's not changing for 7.1.
        regards, tom lane


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