On Tue, May 13, 2014 at 3:33 AM, Fujii Masao <masao.fu...@gmail.com> wrote: > On Sun, May 11, 2014 at 7:30 PM, Simon Riggs <si...@2ndquadrant.com> wrote: >> On 30 August 2013 04:55, Fujii Masao <masao.fu...@gmail.com> wrote: >> >>> My idea is very simple, just compress FPW because FPW is >>> a big part of WAL. I used pglz_compress() as a compression method, >>> but you might think that other method is better. We can add >>> something like FPW-compression-hook for that later. The patch >>> adds new GUC parameter, but I'm thinking to merge it to full_page_writes >>> parameter to avoid increasing the number of GUC. That is, >>> I'm thinking to change full_page_writes so that it can accept new value >>> 'compress'. >> >>> * Result >>> [tps] >>> 1386.8 (compress_backup_block = off) >>> 1627.7 (compress_backup_block = on) >>> >>> [the amount of WAL generated during running pgbench] >>> 4302 MB (compress_backup_block = off) >>> 1521 MB (compress_backup_block = on) >> >> Compressing FPWs definitely makes sense for bulk actions. >> >> I'm worried that the loss of performance occurs by greatly elongating >> transaction response times immediately after a checkpoint, which were >> already a problem. I'd be interested to look at the response time >> curves there. > > Yep, I agree that we should check how the compression of FPW affects > the response time, especially just after checkpoint starts. > >> I was thinking about this and about our previous thoughts about double >> buffering. FPWs are made in foreground, so will always slow down >> transaction rates. If we could move to double buffering we could avoid >> FPWs altogether. Thoughts? > > If I understand the double buffering correctly, it would eliminate the need > for > FPW. But I'm not sure how easy we can implement the double buffering.
There is already a patch on the double buffer write to eliminate the FPW. But It has some performance problem because of CRC calculation for the entire page. http://www.postgresql.org/message-id/1962493974.656458.1327703514780.javamail.r...@zimbra-prod-mbox-4.vmware.com I think this patch can be further modified with a latest multi core CRC calculation and can be used for testing. Regards, Hari Babu Fujitsu Australia -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers