On 08/28/2014 10:10 AM, Michael Paquier wrote:
+ #synchronous_standby_num = -1 # number of standbys servers using sync rep
To be honest, that's a horrible name for the GUC. Back when synchronous replication was implemented, we had looong discussions on this feature. It was called "quorum commit" back then. I'd suggest using the "quorum" term in this patch, too, that's a fairly well-known term in distributed computing for this.
When synchronous replication was added, quorum was left out to keep things simple; the current feature set was the most we could all agree on to be useful. If you search the archives for "quorum commit" you'll see what I mean. There was a lot of confusion on what is possible and what is useful, but regarding this particular patch: people wanted to be able to describe more complicated scenarios. For example, imagine that you have a master and two standbys in one the primary data center, and two more standbys in a different data center. It should be possible to specify that you must get acknowledgment from at least on standby in both data centers. Maybe you could hack that by giving the standbys in the same data center the same name, but it gets ugly, and it still won't scale to even more complex scenarios.
Maybe that's OK - we don't necessarily need to solve all scenarios at once. But it's worth considering.
BTW, how does this patch behave if there are multiple standbys connected with the same name?
- Heikki -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
