Re: Configuring synchronous replication

On Fri, Sep 17, 2010 at 8:31 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> The only thing standby registration allows you to do is know whether
> there was supposed to be a standby there, but yet it isn't there now. I
> don't see that point as being important because it seems strange to me
> to want to wait for a standby that ought to be there, but isn't anymore.

According to what I heard, some people want to guarantee that all the
transactions are *always* written in *all* the synchronous standbys.
IOW, they want to keep the transaction waiting until it has been written
in all the synchronous standbys. Standby registration is required to
support such a use case. Without the registration, the master cannot
determine whether the transaction has been written in all the synchronous
standbys.

> What happens if it never comes back? Manual intervention required.

Yep.

> In the use cases we discussed we had simple 2 or 3 server configs.
>
> master
> standby1 - preferred sync target - set to recv, fsync or apply
> standby2 - non-preferred sync target, maybe test server - set to async
>
> So in the two cases you mention we might set
>
> "wait for ack from reporting slave"
> master: sync_replication = 'recv'   #as default, can be changed
> reporting-slave: sync_replication_service = 'recv' #gives max level
>
> "wait until replayed in the server on the west coast"
> master: sync_replication = 'recv'   #as default, can be changed
> west-coast: sync_replication_service = 'apply' #gives max level

What synchronization level does each combination of sync_replication
and sync_replication_service lead to? I'd like to see something like
the following table.

 sync_replication | sync_replication_service | result
------------------+--------------------------+--------
 async            | async                    | ???
 async            | recv                     | ???
 async            | fsync                    | ???
 async            | apply                    | ???
 recv             | async                    | ???
 ...

Regards,

-- 
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center