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 328312330C for ; Mon, 8 Jul 2019 17:54:35 -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 6ApjYj54-mN4 for ; Mon, 8 Jul 2019 17:54:35 -0400 (EDT) Received: from smtp47.i.mail.ru (smtp47.i.mail.ru [94.100.177.107]) (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 DFC4920E90 for ; Mon, 8 Jul 2019 17:54:34 -0400 (EDT) Date: Tue, 9 Jul 2019 00:54:32 +0300 From: Konstantin Osipov Subject: [tarantool-patches] Re: [PATCH 1/2] swim: pool IO tasks Message-ID: <20190708215432.GB7873@atlas> References: <20190705230136.GD30966@atlas> <609c7e7b-d8f7-413b-752c-94034bfd689b@tarantool.org> <20190708082521.GB24939@atlas> <35c77ced-50ea-faed-7d41-571020fbbfbb@tarantool.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <35c77ced-50ea-faed-7d41-571020fbbfbb@tarantool.org> 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: Vladislav Shpilevoy Cc: tarantool-patches@freelists.org * Vladislav Shpilevoy [19/07/08 22:14]: > > What happens if I create multiple instances of swim library in > > multiple threads? These instances will try to concurrently access > > these members without mutexes. > > How is it possible? SWIM works in TX only. You just can't > create it another thread. It is literally impossible. My point is, the library should either explicitly prohibit it by panicking in swim_new/swim_cfg, or should be resilient to it. Please choose. I'd rather make it not depend on tx or any other thread in particular, it's easier to test. > Even if someday it will work in another thread, still all > the SWIMs will work in one thread. So in future we won't > allow to scatter SWIMs among multiple threads as well. > > With the same reasoning we would need to make thread-local > all global on_replace triggers like on_replace_vinyl_deferred_delete > just in case if in future Vinyl will do DML/DQL in multiple > threads. But why should we do that now? I do not understand. > > >> > >>> > >>> Why not use mempool? > >>> > >>> > >> > >> Because 1) it is an overkill, 2) I don't want to depend on > >> slab allocator, 3) it just does not fit this case, according > >> to mempool description from mempool.h: > >> > >> "Good for allocating tons of small objects of the same size.". > > > > It is also quite decent for allocating many fairly large objects. > > The key point is that the object is of the same size. You can set > > up mempool the right slab size, and in this case it will do > > exactly what you want. > > > > And again - 'many' usually won't be the case. We will have 0-2 SWIMs > in 99% of cases. One internal SWIM for box, and one external created > by a user. Barely we will have more than 10 cached tasks. > > But ok, as you wish. This place is not as critical for me as thread > locality of the pool. At least we reuse existing code. Thread locality > still looks pointless waste of memory for me. OK, wait a second. I thought you're going to have a single task instance for each member. Which means a couple of dozen instances even in a two node cluster. Am I wrong? -- Konstantin Osipov, Moscow, Russia