From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-f174.google.com (mail-lj1-f174.google.com [209.85.208.174]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by dev.tarantool.org (Postfix) with ESMTPS id CEA0B469710 for ; Wed, 6 May 2020 21:56:06 +0300 (MSK) Received: by mail-lj1-f174.google.com with SMTP id e25so3554167ljg.5 for ; Wed, 06 May 2020 11:56:06 -0700 (PDT) Date: Wed, 6 May 2020 21:55:59 +0300 From: Konstantin Osipov Message-ID: <20200506185559.GA2749@atlas> References: <20200403210836.GB18283@tarantool.org> <20200430145033.GF112@tarantool.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200430145033.GF112@tarantool.org> Subject: Re: [Tarantool-patches] [RFC] Quorum-based synchronous replication List-Id: Tarantool development patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Sergey Ostanevich Cc: tarantool-patches@dev.tarantool.org, Vladislav Shpilevoy * Sergey Ostanevich [20/04/30 17:51]: A few more issues: - the spec assumes there is a full mesh. In any other topology electing a leader based on the longest wal can easily deadlock. Yet it provides no protection against non-full-mesh setups. Currently the server can't even detect that this is not a full-mesh setup, so can't check if the precondition for this to work correctly is met. - the spec assumes that quorum is identical to the number of replicas, and the number of replicas is stable across cluster life time. Can I have quorum=2 while the number of replicas is 4? Am I allowed to increase the number of replicas online? What happens when a replica is added, how exactly and starting from which transaction is the leader required to collect a bigger quorum? - the same goes for removing a replica. How is the quorum reduced? -- Konstantin Osipov, Moscow, Russia