On Tue, 2010-09-07 at 11:41 -0400, Tom Lane wrote: > Simon Riggs <si...@2ndquadrant.com> writes: > > On Tue, 2010-09-07 at 10:47 -0400, Tom Lane wrote: > >> Simon Riggs <si...@2ndquadrant.com> writes: > >>> The WAL is sent from master to standby in 8192 byte chunks, frequently > >>> including multiple commits. From standby, one reply per chunk. If we > >>> need to wait for apply while nothing else is received, we do. > >> > >> That premise is completely false. SR does not send WAL in page units. > >> If it did, it would have the same performance problems as the old > >> WAL-file-at-a-time implementation, just with slightly smaller > >> granularity. > > > There's no dependence on pages in that proposal, so don't understand. > > Oh, well you certainly didn't explain it well then. > > What I *think* you're saying is that the slave doesn't send per-commit > messages, but instead processes the WAL as it's received and then sends > a heres-where-I-am status message back upstream immediately before going > to sleep waiting for the next chunk. That's fine as far as the protocol > goes, but I'm not convinced that it really does all that much in terms > of improving performance. You still have the problem that the master > has to fsync its WAL before it can send it to the slave. Also, the > slave won't know whether it ought to fsync its own WAL before replying.
Yes, apart from last sentence. Please wait for the code. -- Simon Riggs www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Training and Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
