Horton

Re: Cost of XLogInsert CRC calculations

Simon Riggs <simon@2ndquadrant.com>

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From: Simon Riggs <simon@2ndquadrant.com>
To: Mark Cave-Ayland <m.cave-ayland@webbased.co.uk>
Cc: 'Christopher Kings-Lynne' <chriskl@familyhealth.com.au>, 'Tom Lane' <tgl@sss.pgh.pa.us>, 'Bruce Momjian' <pgman@candle.pha.pa.us>, pgsql-hackers@postgresql.org
Date: 2005-05-16T18:51:48Z
Lists: pgsql-hackers 
On Mon, 2005-05-16 at 12:12 +0100, Mark Cave-Ayland wrote:
> This now gives the following (correct) result on both platforms:
> 	Win32: 1.8GHz P4, WinXP
> 	Linux: 2.8GHz Xeon, FC1
> 
> 
> 	Win32 UINT64:	0x782104059a01660	(crc0)
> ~158us
> 	Win32 UINT32:	0x78210405 (crc1), 0x59a01660 (crc0)	~58us
> 
> 	FC1 UINT64:		0x782104059a01660 (crc0)
> ~76us
> 	FC1 UINT32:		0x78210405 (crc1), 0x59a01660 (crc0)
> ~29us
> 
> 
> Note that we still find that using the INT64_IS_BUSTED code is over 100%
> quicker than the UINT64 code for CRC64 calculation, and I believe it is not
> being used by default under Linux or Win32 for 32 bit platforms. Of course
> Tom's suggestion of going for CRC32 across the board would hopefully solve
> this entirely and bring the times down a little further too.

I think perhaps that the difference in hardware is the reason for the
difference in elapsed time, not the OS.

The performance gain is disturbing. I think its supposed to be the other
way around isn't it? Like having INT64 is supposed to be good...

Perhaps the BIOS on your systems don't correctly support 64-bit, so
mimicking it costs more. 

Best Regards, Simon Riggs