From: Serge Petrenko via Tarantool-patches <tarantool-patches@dev.tarantool.org> To: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>, Konstantin Osipov <kostja.osipov@gmail.com>, gorcunov@gmail.com, tarantool-patches@dev.tarantool.org Subject: Re: [Tarantool-patches] [PATCH v3] wal: introduce limits on simultaneous writes Date: Tue, 16 Mar 2021 13:19:27 +0300 [thread overview] Message-ID: <07f4831b-2300-2bb0-28a3-9d49f197e951@tarantool.org> (raw) In-Reply-To: <54666e16-f577-c9f5-e917-f834b7e4b8d5@tarantool.org> 16.03.2021 02:42, Vladislav Shpilevoy пишет: > Hi! Thanks for the patch! Thanks for your answer! > > I must admit, it looks kind of ugly :D. The class we have now only remotely > looks like a semaphore. > > Number of reasons, some of which you already listed in the header file: > > - It is advisory. Can be bypassed easily if you forget to check wouldblock. > But not a big issue really. An optional thing like 'try_take' is needed > for box.commit({is_async = true}) anyway, not to block the fiber; > > - You can take more amount of the resource than there is. Bearable as well, > but still; > > - sem_release() does not wakeup anybody. Quite counter-intuitive; > > - The wouldblock check not only checks the resource being available, but also > if there are any waiters. It wouldn't matter for a real semaphore, because > it has nothing to do with ordering the waiters in FIFO. It is a detail of > the journal which slipped into the general class. > But maybe that is the only way to make it fair? Otherwise some fibers > could be blocked forever due to starvation. > > The last thing I am not sure is even an issue. Might be a feature. > > The others probably can be fixed if we would rework journal_queue API. For > instance, not have journal_queue_wait() separated from journal_queue_on_append(). > Then sem_take() could become blocking and obligatory. > > You simply inline everything into journal_write() and journal_write_try_async(), > and you will see that you can always call take() and block inside of it. > > But I don't know if it is worth doing TBH. It is used in a single place so far. > This is hard to define fiber_sem API which would be suitable for future usages. > I would vote for not doing it now and see if we would need the semaphore in the > future. > > Although the idea about removing journal_queue_wait() might be worth trying. > It is used either right before journal_queue_on_append(), or in > journal_queue_flush() which is also right before journal_queue_on_append(). > Up to you. Anyway we need to return to this code for box.commit({is_async}) > feature, which means the hard polishing might be not so useful. Let's drop the semaphore thing then. I removed the commit introducing it and pushed the patch on a new branch: sp/gh-5536-replica-oom-no-sem -- Serge Petrenko
next prev parent reply other threads:[~2021-03-16 10:19 UTC|newest] Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-02-24 19:35 Serge Petrenko via Tarantool-patches 2021-02-24 19:40 ` Serge Petrenko via Tarantool-patches 2021-02-25 13:05 ` Konstantin Osipov via Tarantool-patches 2021-02-26 0:57 ` Vladislav Shpilevoy via Tarantool-patches 2021-02-26 7:18 ` Konstantin Osipov via Tarantool-patches 2021-02-26 20:23 ` Vladislav Shpilevoy via Tarantool-patches 2021-02-26 21:20 ` Konstantin Osipov via Tarantool-patches 2021-02-26 22:44 ` Vladislav Shpilevoy via Tarantool-patches 2021-02-27 13:27 ` Konstantin Osipov via Tarantool-patches 2021-03-01 19:15 ` Serge Petrenko via Tarantool-patches 2021-03-01 21:46 ` Konstantin Osipov via Tarantool-patches 2021-02-26 0:56 ` Vladislav Shpilevoy via Tarantool-patches 2021-03-01 19:08 ` Serge Petrenko via Tarantool-patches 2021-03-01 22:05 ` Vladislav Shpilevoy via Tarantool-patches 2021-03-02 17:51 ` Serge Petrenko via Tarantool-patches 2021-03-03 20:59 ` Vladislav Shpilevoy via Tarantool-patches 2021-03-09 15:10 ` Serge Petrenko via Tarantool-patches 2021-03-09 19:49 ` Vladislav Shpilevoy via Tarantool-patches 2021-03-10 8:18 ` Konstantin Osipov via Tarantool-patches 2021-03-12 17:10 ` Serge Petrenko via Tarantool-patches 2021-03-13 19:14 ` Konstantin Osipov via Tarantool-patches 2021-03-15 23:42 ` Vladislav Shpilevoy via Tarantool-patches 2021-03-16 6:45 ` Konstantin Osipov via Tarantool-patches 2021-03-16 20:27 ` Vladislav Shpilevoy via Tarantool-patches 2021-03-16 10:19 ` Serge Petrenko via Tarantool-patches [this message] 2021-03-16 20:48 ` Vladislav Shpilevoy via Tarantool-patches 2021-03-17 12:14 ` Serge Petrenko via Tarantool-patches 2021-03-17 21:02 ` Vladislav Shpilevoy via Tarantool-patches 2021-03-19 11:32 ` Serge Petrenko via Tarantool-patches 2021-03-19 15:36 ` Kirill Yukhin via Tarantool-patches
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