On 23 January 2016 at 00:51, Andres Freund <and...@anarazel.de> wrote:
> Not propagating them through the WAL also has the rather large advantage > of not barring the way to using such slots on standbys. > Yeah. So you could have a read-replica that has a slot and it has child nodes you can fail over to, but you don't have to have the slot on the master. I don't personally find that to be a particularly compelling thing that says "we must have this" ... but maybe I'm not seeing the full significance/advantages. > I think it's technically quite possible to maintain the required > resources on multiple nodes. The question is how would you configure on > which nodes the resources need to be maintained? I can't come up with a > satisfying scheme... > That's part of it. Also the mechanism by which we actually replicate them - protocol additions for the walsender protocol, how to reliably send something that doesn't have an LSN, etc. It might be fairly simple, I haven't thought about it deeply, but I'd rather not go there until the basics are in place. BTW, I'm keeping a working tree at https://github.com/2ndQuadrant/postgres/tree/dev/failover-slots . Subject to rebasing, history not clean. It has a test script in it that'll go away before patch posting. Current state needs work to ensure that on-disk and in-memory representations are kept in sync, but is getting there. -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
