From: Konstantin Osipov <kostja@tarantool.org> To: tarantool-patches@freelists.org Subject: [tarantool-patches] Re: [PATCH 7/9] vinyl: randomize range compaction to avoid IO load spikes Date: Tue, 5 Feb 2019 20:39:58 +0300 [thread overview] Message-ID: <20190205173958.GG6811@chai> (raw) In-Reply-To: <20190122125458.cutoz5rtfd2sb6el@esperanza> * Vladimir Davydov <vdavydov.dev@gmail.com> [19/01/22 15:56]: > I ran some tests and, surprisingly, it turned out that randomization > didn't help at all: the compaction queue size jumped up to 30% and even > 40% from time to time although there was plenty of compaction power - > compaction threads were busy only half of the time. When I looked > closer, I saw that the queue size behavior looked weird - it jumped > after a dump for a very short period of time, until the next dump, which > pushed it back to 10%. This made me wonder how it could happen at all - > normally, compaction queue should only grow after a dump, not diminish. > I think I've finally found the root cause of the problem. The code > computing compaction priority (see vy_range_update_compaction_priority) > is unstable meaning the size of the first level equals the size of the > smallest run so if memory dumps produce runs of varying sizes, which is > what happens in practice in contrast to simulation, the shape of the > tree will vary as well, resulting in different compaction priority and > unstable queue behavior. > > We must fix this somehow. One way to do it is compute the first level > size basing on the size of the last level run, which is constant most of > the time, and indeed, when I did it and reran the tests, I found that > the queue stayed below 10% all the time. Turning off randomization, made > the queue jump up to 30%, which was expected. The diff is below. I'll > spruce it up a little, wrap it nicely, and submit it separately later. Why not use a simple weighted average? -- Konstantin Osipov, Moscow, Russia, +7 903 626 22 32 http://tarantool.io - www.twitter.com/kostja_osipov
next prev parent reply other threads:[~2019-02-05 17:40 UTC|newest] Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-01-20 21:16 [PATCH 0/9] vinyl: compaction randomization and throttling Vladimir Davydov 2019-01-20 21:17 ` [PATCH 1/9] vinyl: update lsm->range_heap in one go on dump completion Vladimir Davydov 2019-01-24 16:55 ` Vladimir Davydov 2019-02-05 16:37 ` [tarantool-patches] " Konstantin Osipov 2019-01-20 21:17 ` [PATCH 2/9] vinyl: ignore unknown .run, .index and .vylog keys Vladimir Davydov 2019-01-24 16:56 ` Vladimir Davydov 2019-01-20 21:17 ` [PATCH 3/9] vinyl: use uncompressed run size for range split/coalesce/compaction Vladimir Davydov 2019-01-21 9:42 ` Vladimir Davydov 2019-02-05 16:49 ` [tarantool-patches] " Konstantin Osipov 2019-02-06 8:55 ` Vladimir Davydov 2019-02-06 10:46 ` Konstantin Osipov 2019-02-06 10:55 ` Vladimir Davydov 2019-02-05 16:43 ` Konstantin Osipov 2019-02-06 16:48 ` Vladimir Davydov 2019-01-20 21:17 ` [PATCH 4/9] vinyl: rename lsm->range_heap to max_compaction_priority Vladimir Davydov 2019-01-20 21:17 ` [PATCH 5/9] vinyl: keep track of dumps per compaction for each LSM tree Vladimir Davydov 2019-02-05 16:58 ` [tarantool-patches] " Konstantin Osipov 2019-02-06 9:20 ` Vladimir Davydov 2019-02-06 16:54 ` Vladimir Davydov 2019-01-20 21:17 ` [PATCH 6/9] vinyl: set range size automatically Vladimir Davydov 2019-01-22 9:17 ` Vladimir Davydov 2019-02-05 17:09 ` [tarantool-patches] " Konstantin Osipov 2019-02-06 9:23 ` Vladimir Davydov 2019-02-06 17:04 ` Vladimir Davydov 2019-01-20 21:17 ` [PATCH 7/9] vinyl: randomize range compaction to avoid IO load spikes Vladimir Davydov 2019-01-22 12:54 ` Vladimir Davydov 2019-02-05 17:39 ` Konstantin Osipov [this message] 2019-02-06 8:53 ` [tarantool-patches] " Vladimir Davydov 2019-02-06 10:44 ` Konstantin Osipov 2019-02-06 10:52 ` Vladimir Davydov 2019-02-06 11:06 ` Konstantin Osipov 2019-02-06 11:49 ` Vladimir Davydov 2019-02-06 13:43 ` Konstantin Osipov 2019-02-06 14:00 ` Vladimir Davydov 2019-02-05 17:14 ` Konstantin Osipov 2019-01-20 21:17 ` [PATCH 8/9] vinyl: introduce quota consumer types Vladimir Davydov 2019-01-20 21:17 ` [PATCH 9/9] vinyl: throttle tx to ensure compaction keeps up with dumps Vladimir Davydov 2019-01-21 14:14 ` Vladimir Davydov 2019-01-22 9:09 ` Vladimir Davydov
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