Re: write ahead logging in standby (streaming replication)

Fujii Masao wrote:
> Personally, I think that semi-synchronous replication is sufficient for HA.
>
Whether or not you think it's sufficient for what you have in mind,
"synchronous replication" requires a return ACK from the secondary
before you say things are committed on the primary. If you don't do
that, it's not true sync replication anymore; it's asynchronous
replication. Plenty of people decide that a local commit combined with
a promise to synchronize as soon as possible to the slave is good enough
for their apps, which as you say is getting referred to as
"semi-synchronous replication" nowadays. That's an awful name though,
because it's not true--that's asynchronous replication, just aiming for
minimal lag. It's OK to say that's what you want, but you can't say
it's really a synchronous commit anymore if you do things that way.

--
Greg Smith 2ndQuadrant Baltimore, MD
PostgreSQL Training, Services and Support
greg(at)2ndQuadrant(dot)com www.2ndQuadrant.com