On 10/08/2014 11:47 AM, furu...@pm.nttdata.co.jp wrote:
On 10/08/2014 07:23 AM, furu...@pm.nttdata.co.jp wrote:
What set of options would you pass if you want to use it as a
synchronous standby? And if you don't? Could we just have a single
"--synchronous"
flag, instead of -F and --reply-fsync?
If you set "synchronous_commit" as "remote_write", the options would
be different .
The set of options in each case, see the following.
Synchronous standby(synchronous_commit=on)
--fsync-interval=-1
--reply-fsync
--slot=slotname
Synchronous standby(synchronous_commit=remote_write)
--fsync-interval=-1
--reply-fsync
Asynchronous
There are no relative options.
Well, if the response time delay(value of
"--status-interval=interval") is acceptable, "--reply-fsync" is
unnecessary.
Instead of "--reply-fsync", using "--synchronous"(which summarizes
the "--reply-fsync" and "fsync-interval = -1") might be easy to
understand. Although, in that case, "--fsync-interval=interval" would
be fixed value. Isn't there any problem ?
I think we should remove --fsync-interval and --reply-fsync, and just
have a --synchronous option, which would imply the same behavior you get
with --fsync-interval=-1 --reply--fsync.
That leaves the question of whether pg_receivexlog should do fsyncs when
it's not acting as a synchronous standby. There isn't any real need to
do so. In asynchronous mode, there are no guarantees anyway, and even
without an fsync, the OS will eventually flush the data to disk.
But we could do even better than that. It would be best if you didn't
need even the --synchronous flag. The server knows whether the client
is a synchronous standby or not. It could tell the client.
If we remove --fsync-interval, resoponse time to user will not be delay.
Although, fsync will be executed multiple times in a short period.
And there is no way to solve the problem without --fsync-interval, what should
we do about it?
I'm sorry, I didn't understand that.
In asynchronous mode, I think there is no problem since the specification is
same with release version.
The server knows whether the client is a synchronous standby or not.
It could tell the client.
When notifying the synchronous/asynchronous mode to the client from the server,
do we need to change the format of the Message ?
Yeah. Or rather, add a new message type, to indicate the
synchronous/asynchronous status.
- Heikki
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