Re: Issues with two-server Synch Rep

On Mon, 2010-10-11 at 11:07 -0700, Josh Berkus wrote:

> Absolutely.  For a synch standby, you can't tolerate any standby delay
> at all.  This means that anywhere from 1/4 to 3/4 of queries on the
> standby would be cancelled on any high-traffic OLTP server.  Hence,
> "useless".

Don't agree with your numbers there and you seem to be assuming no
workarounds would be in use. A different discussion, I think.

> Interaction?  My opinion is that the two are completely incompatible.
> You can't have synch rep and also have standby_delay > 0.

I would agree that adding an "apply" mode only makes sense when we have
master feedback to ensure that standby delay is minimised. But that's
not the only use case for sync rep and it doesn't actually help that
much. 

Adding the feedback channel looks trivial to me, once we've got the main
sync rep patch in. I'll handle that.

For this reason, I've removed the "apply" mode from my patch, for now. I
want to get the simplest possible patch agreed and then add things
later.

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Development, 24x7 Support, Training and Services