On 2014-04-16 18:51:41 +0200, Magnus Hagander wrote: > I'm thinking it could be interesting to know how many times (or in some > other useful unit than "times" - how often) a specific replication slot has > "blocked" xlog rotation. Since this AFAIK only happens during checkpoints, > it seems it should be "reasonably cheap" to track? It would serve as an > indicator of which slave(s) are having enough trouble keeping up to > potentially cause issues.
The xlog removal code just check the "global minimum" required LSN - it doesn't check the individual slots. So you'd need to add a bit more code to that location. But it'd be easy.
Do we have statistics there somewhere - how often that global minimum blocks something? That on it's own might be a start :)
But I think I'd just monitor/graph the byte difference for all slots using pg_replication_slots...
Yeah, that would work when monitored continously. I was more looking for the view of "hey, could this be what happened" into a system that did not previously have any monitoring installed and therefor no such history.