From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [tarantool-patches] Re: [PATCH rfc] schema: add possibility to find and throw away dead replicas References: <20180921182503.14027-1-arkholga@tarantool.org> <20180926144658.dru6pw44e33nnnpi@esperanza> <20a60b35-1615-4b26-c0f6-032530ac3b1b@tarantool.org> <20180927090446.i7gf22lqtzkvykal@esperanza> From: Olga Arkhangelskaia Message-ID: <43514e84-d226-0850-5d1f-161d41a3f491@tarantool.org> Date: Thu, 27 Sep 2018 13:27:23 +0300 MIME-Version: 1.0 In-Reply-To: <20180927090446.i7gf22lqtzkvykal@esperanza> Content-Type: text/plain; charset="utf-8"; format="flowed" Content-Transfer-Encoding: 8bit Content-Language: ru To: Vladimir Davydov Cc: tarantool-patches@freelists.org, georgy@tarantool.org List-ID: 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. > >>> 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 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? >>> last time so that the function would work instantly. >>> The time should probably be persisted so that restarts wouldn't >>> affect the way the function works.