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.

But the confirmation that needs to come is that the WAL changes have
been applied (fsync'ed), so the performance will be terrible.  So bad,
that I don't think anyone will want to use such a replication system ...

Alvaro Herrera                      
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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