Although, if we fixed that the leader sometimes publishes state for replicas (which I think is a mistake, I worked hard initially to avoid a node ever publishing state for another node) you could at least track the last state Published and avoid repeating it over and over pretty easily. On Wed, Nov 23, 2016 at 6:03 PM Mark Miller <[email protected]> wrote:
> I didn't say stale state though actually. I said state progressions. > On Wed, Nov 23, 2016 at 6:03 PM Mark Miller <[email protected]> wrote: > > Because that's how it works. > On Wed, Nov 23, 2016 at 5:57 PM Walter Underwood <[email protected]> > wrote: > > Why would other nodes need to see stale state? > > If they really need intermediate state changes, that sounds like a problem. > > wunder > Walter Underwood > [email protected] > http://observer.wunderwood.org/ (my blog) > > > On Nov 23, 2016, at 2:53 PM, Mark Miller <[email protected]> wrote: > > In many cases other nodes need to see a progression of state changes. You > really have to clear the deck and try to start from 0. > On Wed, Nov 23, 2016 at 5:50 PM Walter Underwood <[email protected]> > wrote: > > If the queue is local and the state messages are complete, the local queue > should only send the latest, most accurate update. The rest can be skipped. > > The same could be done on the receiving end. Suck the queue dry, then > choose the most recent. > > If the updates depend on previous updates, it would be a lot more work to > compile the latest delta. > > wunder > > Walter Underwood > [email protected] > http://observer.wunderwood.org/ (my blog) > > > On Nov 23, 2016, at 2:45 PM, Mark Miller <[email protected]> wrote: > > I talked about this type of thing with Jessica at Lucene / Sole > revolution. One thing is, when you reconnect after connecting to ZK, it > should now efficiently set every core as down in a single command, not each > core. Beyond that, any single node knows how fast it's sending overseer > updates. Each should have a governor. If the rate is too high, a node > should know it's best to just forgive up and assume things are screwed. It > could try and reset from ground zero. > > There are other things things that can be done, but given the current > design, the simplest win is that a replica can easily prevent itself from > spamming the overseer queue. > > Mark > On Wed, Nov 23, 2016 at 5:05 PM Scott Blum <[email protected]> wrote: > > I've been fighting fires the last day where certain of our solr nodes will > have a long GC pauses that cause them to lose their ZK connection and have > to reconnect. That would be annoying, but survivable, although obvious > it's something I want to fix. > > But what makes it fatal is the current design of the state update queue. > > Every time one of our nodes flaps, it ends up shoving thousands of state > updates and leader requests onto the queue, most of them ultimately > futile. By the time the state is actually published, it's already stale. > At one point we had 400,000 items in the queue and I just had to declare > bankruptcy, delete the entire queue, and elect a new overseer. Later, we > had 70,000 items from several flaps that took an hour to churn through. > even after I'd shut down the problematic nodes. Again, almost entirely > useless, repetitive work. > > Digging through ZKController and related code, the current model just > seems terribly outdated and non-scalable now. If a node flaps for just a > moment, do we really need to laboriously update every core's state down, > just to mark it up again? What purpose does this serve that isn't already > served by the global live_nodes presence indication and/or leader election > nodes? > > Rebooting a node creates a similar set of problems, a couple hundred cores > end up generating thousands of ZK operations to just to back to normal > state. > > We're at enough of breaking point that I *have* to do something here for > our own cluster. I would love to put my head together with some of the > more knowledgeable Solr operations folks to help redesign something that > could land in master and improve scalability for everyone. I'd also love > to hear about any prior art or experiments folks have done. And if there > are already efforts in process to address this very issue, apologies for > being out of the loop. > > Thanks! > Scott > > -- > - Mark > about.me/markrmiller > > > -- > - Mark > about.me/markrmiller > > > -- > - Mark > about.me/markrmiller > > -- > - Mark > about.me/markrmiller > -- - Mark about.me/markrmiller
