On Tue, Dec 16, 2014 at 3:46 AM, Robert Haas <robertmh...@gmail.com> wrote: > On Sat, Dec 13, 2014 at 9:36 AM, Michael Paquier > <michael.paqu...@gmail.com> wrote: >> Something to be aware of btw is that this patch introduces an >> additional 8 bytes per block image in WAL as it contains additional >> information to control the compression. In this case this is the >> uint16 compress_len present in XLogRecordBlockImageHeader. In the case >> of the measurements done, knowing that 63638 FPWs have been written, >> there is a difference of a bit less than 500k in WAL between HEAD and >> "FPW off" in favor of HEAD. The gain with compression is welcome, >> still for the default there is a small price to track down if a block >> is compressed or not. This patch still takes advantage of it by not >> compressing the hole present in page and reducing CPU work a bit. > > That sounds like a pretty serious problem to me. OK. If that's so much a problem, I'll switch back to the version using 1 bit in the block header to identify if a block is compressed or not. This way, when switch will be off the record length will be the same as HEAD. -- Michael
-- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
