Re: Cost of XLogInsert CRC calculations

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