| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Markus Schiltknecht <markus(at)bluegap(dot)ch> |
| Cc: | AgentM <agentm(at)themactionfaction(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Replication |
| Date: | 2006-08-21 18:46:41 |
| Message-ID: | 1156186001.15743.22.camel@dogma.v10.wvs |
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| Lists: | pgsql-hackers |
On Mon, 2006-08-21 at 19:42 +0200, Markus Schiltknecht wrote:
> Jeff Davis wrote:
> > How does WAL shipping help synchronous replication?
>
> The WAL is written _before_ commit, logging all the changes the
> transaction wants to write to the disk. This makes it look very similar
> to what is needed for synchronous replication.
>
> Instead of waiting for confirmation from the disk, that your WAL has
> been written, you would have to wait from the network to confirm that
> the changes have been delivered via the network.
Synchronous replication (to me) means that the data has been written to
permanent storage on all masters and all slaves before any master or
slave reports a successful COMMIT. Are you suggesting that you ship the
WAL over the network, wait for it to be written to the slave, and then
report a successful commit?
Regards,
Jeff Davis
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