From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 27 Sep 2018 13:54:58 +0300 From: Vladimir Davydov Subject: Re: [tarantool-patches] Re: [PATCH rfc] schema: add possibility to find and throw away dead replicas Message-ID: <20180927105458.duu75inzgwz7mer5@esperanza> References: <20180921182503.14027-1-arkholga@tarantool.org> <20180926144658.dru6pw44e33nnnpi@esperanza> <20a60b35-1615-4b26-c0f6-032530ac3b1b@tarantool.org> <20180927090446.i7gf22lqtzkvykal@esperanza> <43514e84-d226-0850-5d1f-161d41a3f491@tarantool.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <43514e84-d226-0850-5d1f-161d41a3f491@tarantool.org> To: Olga Arkhangelskaia Cc: tarantool-patches@freelists.org, georgy@tarantool.org List-ID: On Thu, Sep 27, 2018 at 01:27:23PM +0300, Olga Arkhangelskaia wrote: > > > 27/09/2018 12:04, Vladimir Davydov пишет: > > On Thu, Sep 27, 2018 at 10:37:57AM +0300, Olga Arkhangelskaia wrote: > > > > > > 26/09/2018 17:46, Vladimir Davydov пишет: > > > > On Fri, Sep 21, 2018 at 09:25:03PM +0300, Olga Arkhangelskaia wrote: > > > > > Adds possibility to get list of alive replicas in a replicaset, > > > > > prune from box.space_cluster those who is not considered as alive, > > > > > and if one has doubts see state of replicaset. > > > > > > > > > > Replica is considered alive if it is just added, its status after > > > > > timeout period is not stopped or disconnected. However it it has both > > > > > roles (master and replica) we consider such instance dead only if its > > > > > upstream and downstream status is stopped or disconnected. > > > > > > > > > > If replica is considered dead we can prune its uuid from _cluster space. > > > > > If one not sure if the replica is dead or is there is any activity on it > > > > > it is possible to list replicas with its role, status and lsn > > > > > statistics. > > > > > > > > > > If you have some ideas how else we can/should decide whether replica is dead > > > > > please share. > > > > > > > > > > Closes #3110 > > > > > --- > > > > > > > > > > https://github.com/tarantool/tarantool/issues/3110 > > > > > https://github.com/tarantool/tarantool/tree/OKriw/gh-3110-prune-dead-replica-from-replicaset-1.10 > > > > A documentation request with the new API description is missing. > > > > Tests don't pass on Travis CI. > > > > > > > > Regarding the code: > > > > > > > > 1. Why do you add a function that lists *alive* replicas? The issue > > > > author didn't ask for that. He asked for a script that would delete > > > > dead replicas from the _cluster system space. We might want to add a > > > > function that would list *dead* replicas so that he/she could check > > > > what replicas would be deleted (aka "dry run"), but it doesn't make > > > > sense to list alive replicas. > > > It is easy to change, but as I understood we need to throw away replica. > > How does it contradict what I said? > It does not. Just explain why I did it in such a way. Talked to Georgy. We agreed that it's worth adding three methods: prune_replicas - delete replicas given in arguments list_dead_replicas - returns a table with UUIDs of supposedly dead replicas prune_dead_replicas - prune_replicas(list_dead_replics()) (Function names might need some polishing) > > > > > > 2. Dead replica detection is utterly ridiculuous: the functions sleeps > > > > for the given amount of time and then deletes inactive replicas. > > > > As a user, I'd want to have an ability to delete replicas that have > > > > been inactive for, say, a day. Does this mean that I have to wait > > > > for a whole day before this function completes? Obviously, no. > > > > I guess tarantool core should keep track of the time each replica > > > > was active > > > So we need changes in core code? About lastt time of activity, what do you > > > mean? Lasn change, vclock, status? > > Real time when the replica was last active. > I still did not get "active". Is it when writes occure at the specified > replica? > And last time it got updates from master? I think we should maintain two times. When the relay was last active and when the applier was last active. > I think I will write you in privat to discuss. > > > > > > If replica is dead for long perion of time we can see its status. And as I > > > undestand we have heartbeat to monitor the connecion, so if there is > > > problems with it - we see status. > > Disconnected status only means that the replica is not available > > right now. We want to delete replicas that haven't been active for > > the specified amount of time, say a day or even a week. > > Good point. I will try to do. > > > > BTW, forgot to mention: this function should probably be defined in > > box.ctl. > > Why ctl? Because ctl namespace is meant to store helper functions.