Re: Timeout and wait-forever in sync rep

On Fri, 2010-10-15 at 21:41 +0900, Fujii Masao wrote:

> As the result of the discussion, I think that we need the following two
> parameters for the case where the standby goes down.

> * replication_timeout
> This is the maximum time to wait for the ACK from the standby. If this
> timeout expires, the master closes the replication connection and
> disconnects the standby. This parameter is just used for the master
> to detect the standby crash or the network outage.
>
> We already have keepalive parameters for that purpose.

Yes, I had thought we would just use the keepalives...

> But they cannot
> detect the disconnection in some cases. So replication_timeout needs
> to be introduced for sync rep.

When exactly don't the keepalives work?

> * allow_standalone_master
> This specifies whether we allow the master to process transactions
> alone when there is no connected and sync'd standby.
>
> If this is false, all the transactions on the master are blocked until
> sync'd standby has appeared. Of course, this happen not only when
> replication_timeout expires but also when we start the master alone
> at the initial setup, when the master detects the disconnection by
> using keepalive parameters, and when the standby is shut down normally.
> People who want 'wait-forever' will disable this parameter to reduce
> the risk of data loss.
>
> OTOH, if this is true, the absence of sync'd standby doesn't prevent
> the master from processing transactions alone. People who want high
> availability even though the risk of data loss increases will enable
> this parameter.

OK

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