From: Serge Petrenko via Tarantool-patches <tarantool-patches@dev.tarantool.org> To: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>, Cyrill Gorcunov <gorcunov@gmail.com> Cc: tml <tarantool-patches@dev.tarantool.org> Subject: Re: [Tarantool-patches] [PATCH v27 2/3] qsync: order access to the limbo terms Date: Thu, 13 Jan 2022 13:13:07 +0300 [thread overview] Message-ID: <5cc5a52d-e6a7-b4cc-d2a1-23a9b1758288@tarantool.org> (raw) In-Reply-To: <63f0bdcc-4ab1-6fa9-411f-ddce6e0aa215@tarantool.org> 13.01.2022 00:30, Vladislav Shpilevoy пишет: > Hi! > > On 12.01.2022 15:01, Serge Petrenko wrote: >> >> 11.01.2022 23:39, Cyrill Gorcunov пишет: >>> On Mon, Jan 10, 2022 at 05:28:43PM +0300, Serge Petrenko wrote: >>>> Hi! Thanks for the patch! >>>> box_issue_promote() and box_issue_demote() need fine-grained locking >>>> anyway. >>>> Otherwise it’s possible that promote() is already issued, but not yet >>>> written to WAL, and some >>>> outdated request is applied by applier at that exact moment. >>> True. And in previous series Vlad has asked to not move in code which is >>> not covered by tests. So I think this is a task for the next part. Currently >>> we cover only the race between appliers. >> Let's ask Vlad, then. >> >> I feel like we should fix this now, not waiting for a full fine-grained locking >> patch. >> >> First of all, this is a known bug (and fine-grained locking was meant to >> cover everything we don't know of, just in case). > I am not sure I understand what you both are talking about here. Sergey, do > you mean 'fine-grained locking' as big critical sections covering a lot of > code at once or as many small critical sections? I mean "locking every limbo function", like Cyrill tried to do that in the previous patch version. > > I am confused because of this sentence. "Cover everything we don't know" is > rather opposite to fine-grained locking. I voted for big locks because > apparently it was too hard to implement smaller more precise locks. > >> Besides, simply locking issue_promote/issue_demote should be >> much easier than implementing the fine-grained locking patch. > Yes. I remember the proposal was to lock entire promote/demote and other > qsync/raft functions from beginning to end. Because it should be relatively > easy. I didn't look at the code in this patch though, can't comment it. This particular patch only locks applier_apply_synchro_request(), txn_limbo_process() and txn_limbo_is_replica_outdated(), so that applier cannot apply a request from an already stale term. My proposal is to lock box_issue_promote() and box_issue_demote() (not whole promote/demote) to get rid of another race: when promote is written to WAL, but not yed processed. What you're talking about is what I call "fine grained locking", and it turned out rather hard to implement, so Cyrill abandoned this idea for now. -- Serge Petrenko
next prev parent reply other threads:[~2022-01-13 10:13 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-12-30 20:23 [Tarantool-patches] [PATCH v27 0/3] qsync: implement packet filtering (part 1) Cyrill Gorcunov via Tarantool-patches 2021-12-30 20:23 ` [Tarantool-patches] [PATCH v27 1/3] latch: add latch_is_locked helper Cyrill Gorcunov via Tarantool-patches 2021-12-30 20:23 ` [Tarantool-patches] [PATCH v27 2/3] qsync: order access to the limbo terms Cyrill Gorcunov via Tarantool-patches 2022-01-10 14:28 ` Serge Petrenko via Tarantool-patches 2022-01-11 20:39 ` Cyrill Gorcunov via Tarantool-patches 2022-01-12 14:01 ` Serge Petrenko via Tarantool-patches 2022-01-12 21:30 ` Vladislav Shpilevoy via Tarantool-patches 2022-01-13 10:13 ` Serge Petrenko via Tarantool-patches [this message] 2022-01-13 23:32 ` Vladislav Shpilevoy via Tarantool-patches 2022-01-14 10:20 ` Serge Petrenko via Tarantool-patches 2022-01-14 10:33 ` Cyrill Gorcunov via Tarantool-patches 2021-12-30 20:23 ` [Tarantool-patches] [PATCH v27 3/3] test: add gh-6036-qsync-order test Cyrill Gorcunov via Tarantool-patches 2022-01-10 14:29 ` Serge Petrenko via Tarantool-patches 2022-01-11 20:41 ` Cyrill Gorcunov via Tarantool-patches
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