From: Konstantin Osipov <kostja@tarantool.org> To: Olga Arkhangelskaia <arkholga@tarantool.org> Cc: tarantool-patches@freelists.org Subject: [tarantool-patches] Re: [PATCH v2 1/2] box: added replication_dead/rw_gap options Date: Wed, 24 Oct 2018 19:49:17 +0300 [thread overview] Message-ID: <20181024164917.GA12973@chai> (raw) In-Reply-To: <1540319544.538448282@f372.i.mail.ru> * Olga Arkhangelskaia <arkholga@tarantool.org> [18/10/23 21:41]: > >> In scope of gh-3110 we need options that store periods of time, > >> to be compared with time of last activity of relay and applier. > >> This patch introduces replication_dead_gap and replication_rw_gap options. > >> > >> replication_dead_gap is configured in box.cfg, with default 0 value. > >> If time that passed from now till last reader/writer activity of given replica > >> exceeds replication_dead_gap value, replica is suspected to be dead. > >> replication_dead_gap is measured in hours. > >> > >> replication_rw_gap is configured in box.cfg, with default 0 value. > >> If time difference between last reader activity and last writer activity of > >> given replica exceeds replication_rw_gap value, replica is suspected to be dead. > >> replication_rw_gap is measured in hours. > > Why do we need this if we have heartbeats? > I used to think that we need some parameters, that can be set by user, > to check that replica is not active. > For example, if replica is not active for XXXX seconds - it is dead. > However, I did not think about the idea of passing this parameter as a > function argument: list_dead_replicas(XXXX). So I will throw it away. OK. > > Another question that is worth to discuss - is kind of statistics to use > for accusing replica to be dead. > The is two ways - save time of last write/read by applier and relay. I > implemented it, but as Vova pointed out, may be we need to save period > of time that replica spends in stopped status. So we decided to do > statistics in separate patch set, and implement both way. And than > decide. However, may be you have better ideas, etc. I think unless this statistics is persistent it is of little value. > > And with swim on board we will have gossip information about entire replica set? > I have read about swim, and as I understand it : > if we have replica set with some topology except full-mesh, we can save > dead replicas mask, numbers, etc, (that we obtained using > list_dead_replicas on some of replicas), and in the end, after some > questioning, we will definitely have information about every replica > in the set. > If that what you mean. > If not, can you be more specific. We can simply query which replicas are dead according to swim and correlate this information with relay state. If a replica is dead according to relay/applier state and it's dead according to swim, it's dead. -- Konstantin Osipov, Moscow, Russia, +7 903 626 22 32 http://tarantool.io - www.twitter.com/kostja_osipov
next prev parent reply other threads:[~2018-10-24 16:49 UTC|newest] Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-10-23 18:32 [tarantool-patches] " Olga Arkhangelskaia 2018-10-24 16:49 ` Konstantin Osipov [this message] -- strict thread matches above, loose matches on Subject: below -- 2018-10-12 19:45 [tarantool-patches] [PATCH v2 0/2] detect and throw away dead replicas Olga Arkhangelskaia 2018-10-12 19:45 ` [tarantool-patches] [PATCH v2 1/2] box: added replication_dead/rw_gap options Olga Arkhangelskaia 2018-10-23 7:10 ` [tarantool-patches] " Konstantin Osipov
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