On Wed, 9 May 2007, Jignesh Shah wrote:

But we still pay the penalty on WAL while writing them in the first place I guess .. Is there an option to disable it.. I can test how much is the impact I guess couple of %s but good to verify :-) )

on modern CPU's where the CPU is significantly faster then RAM, calculating a checksum is free if the CPU has to touch the data anyway (cycles where it would be waiting for a cache miss are spent doing the calculations)

if you don't believe me, hack the source to remove the checksum and see if you can measure any difference.

David Lang

 >
Regards,
Jignesh


Alvaro Herrera wrote:
 Jignesh Shah escribió:


>  Now comes the thing that I am still exploring
> * Do we do checksum in WAL ? I guess we do .. Which means that we are > now doing double checksumming on the data. One in ZFS and one in > postgresql. ZFS does allow checksumming to be turned off (but on new > blocks allocated). But of course the philosophy is where should it be > done (ZFS or PostgreSQL). >
 Checksums on WAL are not optional in Postgres, because AFAIR they are
 used to determine when it should stop recovering.



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