Re: Compression of full-page-writes

On 30.08.2013 05:55, Fujii Masao wrote:
> * Result
>    [tps]
>    1386.8 (compress_backup_block = off)
>    1627.7 (compress_backup_block = on)

It would be good to check how much of this effect comes from reducing 
the amount of data that needs to be CRC'd, because there has been some 
talk of replacing the current CRC-32 algorithm with something faster. 
See 
http://www.postgresql.org/message-id/20130829223004.GD4283@awork2.anarazel.de. 
It might even be beneficial to use one routine for full-page-writes, 
which are generally much larger than other WAL records, and another 
routine for smaller records. As long as they both produce the same CRC, 
of course.

Speeding up the CRC calculation obviously won't help with the WAL volume 
per se, ie. you still generate the same amount of WAL that needs to be 
shipped in replication. But then again, if all you want to do is to 
reduce the volume, you could just compress the whole WAL stream.

- Heikki