From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from localhost (localhost [127.0.0.1]) by turing.freelists.org (Avenir Technologies Mail Multiplex) with ESMTP id C7C382B72B for ; Wed, 24 Oct 2018 12:49:33 -0400 (EDT) Received: from turing.freelists.org ([127.0.0.1]) by localhost (turing.freelists.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id TLYQnTY5W--X for ; Wed, 24 Oct 2018 12:49:33 -0400 (EDT) Received: from smtp41.i.mail.ru (smtp41.i.mail.ru [94.100.177.101]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by turing.freelists.org (Avenir Technologies Mail Multiplex) with ESMTPS id 347E12B5A1 for ; Wed, 24 Oct 2018 12:49:33 -0400 (EDT) Date: Wed, 24 Oct 2018 19:49:17 +0300 From: Konstantin Osipov Subject: [tarantool-patches] Re: [PATCH v2 1/2] box: added replication_dead/rw_gap options Message-ID: <20181024164917.GA12973@chai> References: <1540319544.538448282@f372.i.mail.ru> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1540319544.538448282@f372.i.mail.ru> Sender: tarantool-patches-bounce@freelists.org Errors-to: tarantool-patches-bounce@freelists.org Reply-To: tarantool-patches@freelists.org List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: tarantool-patches List-subscribe: List-owner: List-post: List-archive: To: Olga Arkhangelskaia Cc: tarantool-patches@freelists.org * Olga Arkhangelskaia [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