Re: Synchronous Standalone Master Redoux

On Tue, Jul 10, 2012 at 9:28 AM, Shaun Thomas <sthomas(at)optionshouse(dot)com> wrote:

> Async is simply too slow for our OLTP system except for the disaster
> recovery node, which isn't expected to carry on within seconds of the
> primary's failure. I briefly considered sync mode when it appeared as a
> feature, but I see it's still too early in its development cycle, because
> there are no degraded operation modes. That's fine, I'm willing to wait.

But this is where some of us are confused with what your asking for.
async is actually *FASTER* than sync. It's got less over head.
Synchrounous replication is basicaly async replication, with an extra
overhead, and an artificial delay on the master for the commit to
*RETURN* to the client. The data is still committed and view able to
new queries on the master, and the slave at the same rate as with
async replication. Just that the commit status returned to the client
is delayed.

So the "async is too slow" is what we don't understand.

> I just don't understand the push-back, I guess. RAID-1 is the poster child
> for synchronous writes for fault tolerance. It will whine constantly to
> anyone who will listen when operating only on one device, but at least it
> still works. I'm pretty sure nobody would use RAID-1 if its failure mode
> was: block writes until someone installs a replacement disk.

I think most of us in the "synchronous replication must be syncronous
replication" camp are there because the guarantees of a simple RAID 1
just isn't good enough for us ;-)

a.

--
Aidan Van Dyk Create like a god,
aidan(at)highrise(dot)ca command like a king,
http://www.highrise.ca/ work like a slave.