Horton

Re: Cost of XLogInsert CRC calculations

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Mark Cave-Ayland <m.cave-ayland@webbased.co.uk>, pgsql-hackers@postgresql.org
Date: 2005-03-08T01:50:01Z
Lists: pgsql-hackers 
Simon Riggs <simon@2ndquadrant.com> writes:
> Well, we're using the CRC in 3 separate places...
> (1) for xlog records
> (2) for complete blocks copied to xlog
> (3) for control files

> For (1), records are so short that probably CRC16 would be sufficient
> without increasing the error rate noticeably.

> I think I'd like to keep (3) at CRC64...its just too important. Plus
> thats slightly less code to change.

The control files are so short that CRC16 would be plenty.

> My money is on (2) being the source of most of that run-time anyway,

Undoubtedly, so there's not going to be much win from micro-optimization
by having several different CRC functions.  I would go for CRC32 across
the board, myself.

			regards, tom lane