On Wed, Feb 17, 2010 at 06:55, Fujii Masao <masao.fu...@gmail.com> wrote: > On Wed, Feb 17, 2010 at 6:28 AM, Magnus Hagander <mag...@hagander.net> wrote: >> If you send me your amazon id, I can get you premissions on my private >> image. I plan to clean it up and make it public, just haven't gotten >> around to it yet... > > Thanks for your concern! I'll send the ID when I complete the preparation.
ok. > And, fortunately?, when I set wal_sync_method to open_sync, the problem was > reproduced in the linux, too. The cause is that the data that is written by Ah, that's good. It always helps if it's a cross-platform issue - particularly in that it's not one of the funky win32 specific things we did :) > walreceiver is not aligned, even if O_DIRECT is used. On win32, O_DIRECT is > used by default. So the problem always happened on win32. Ahh. I see. > I propose two solution ideas: > > 1. O_DIRECT is somewhat harmful in the standby since the data written by > walreceiver is read by the startup process immediately. So, how about > not making only walreceiver use O_DIRECT? In that case, O_DIRECT would be counterproductive, no? It maps to FILE_FLAG_NOI_BUFFERING, which makes sure it doesn't go into the cache. So the read in the startup proc is actually guaranteed to reuqire a physical read - of something we just wrote, so it'll almost certainly end up waiting for a rotation, no? Seems like getting rid of O_DIRECT here is the right thing to do, regardless of this. > 2. Straightforwardly observe the alignment rule. Since the received WAL > data might start at the middle of WAL block, walreceiver needs to keep > the last half-written WAL block for alignment. OTOH since the received > data might end at the middle of WAL block, walreceiver needs zero-padding. > As a result, walreceiver writes the set of the last WAL block, received > data and zero-padding. May there be other reasons to d this as well? -- Magnus Hagander Me: http://www.hagander.net/ Work: http://www.redpill-linpro.com/ -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
