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From "Ilya Pronin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MESOS-184) Log has a space leak
Date Fri, 27 Jul 2018 20:15:00 GMT

    [ https://issues.apache.org/jira/browse/MESOS-184?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16560273#comment-16560273
] 

Ilya Pronin commented on MESOS-184:
-----------------------------------

Discussion at the dev@ mailing list: https://lists.apache.org/thread.html/a0a58e42cbb8dd92dcebbedaa2556e8460a005d4a7cdb2ce1205d04a@%3Cdev.mesos.apache.org%3E

Review requests:
https://reviews.apache.org/r/68089/
https://reviews.apache.org/r/68090/

> Log has a space leak
> --------------------
>
>                 Key: MESOS-184
>                 URL: https://issues.apache.org/jira/browse/MESOS-184
>             Project: Mesos
>          Issue Type: Bug
>          Components: c++ api, replicated log
>    Affects Versions: 0.9.0, 0.14.0, 0.14.1, 0.14.2, 0.15.0, 0.16.0, 0.17.0, 0.18.0, 0.18.1,
0.18.2, 0.19.0
>            Reporter: John Sirois
>            Assignee: Ilya Pronin
>            Priority: Minor
>              Labels: twitter
>
> In short, the access pattern of the Log of the underlying LevelDB storage is such that
background compactions are ineffective and a long running Log will have a space leak on disk
even in the presence of otherwise apparently sufficient Log::Writer::truncate calls.
> It seems the right thing to do is to issue a DB::CompactRange(NULL, Slice(truncateToKey))
after a replica learns a Action::TRUNCATE Record.  The cost here is a synchronous compaction
stall on every truncate so maybe this should be a configuration option or even an explicit
api.
> ===
> Snip of email explanation:
> I spent some time understanding what was going on here and our use pattern of leveldb
does in fact defeat the backround compaction algorithm.
> The docs are here: http://leveldb.googlecode.com/svn/trunk/doc/impl.html in the 'Compactions'
section, but in short the gist is compaction operates on an uncompacted file from a level
(1 file) + all files overlapping its key range in the next level.  Since we write sequential
keys with no randomness at all, by definition the only overlap we ever can get is in level
0 which is the only level that leveldb allows for overlap in sstables in the 1st place.
> That leaves the question of why no compaction on open.  Looking there: http://code.google.com/p/leveldb/source/browse/db/db_impl.cc#1376
> I see a call to MaybeScheduleCompaction, but following that trail, that just leads to
http://code.google.com/p/leveldb/source/browse/db/version_set.cc?spec=svnbc1ee4d25e09b04e074db330a41f54ef4af0e31b&r=36a5f8ed7f9fb3373236d5eace4f5fea369856ee#1156
which implements the compaction strategy I tried to summarize above, and thus background compactions
for out case are limited to level0 -> level 1 compactions and lefel1 and higher never compact
automatically.
> This seems born out by the LOG files.  For example, from smf1-prod - restarts after your
manual compaction fix in bold:
> [jsirois@smf1-ajb-35-sr1 ~]$ grep Compacting /var/lib/mesos/scheduler_db/mesos_log/LOG.old

> 2012/04/13-00:24:20.356673 44c1e940 Compacting 3@0 + 4@1 files
> 2012/04/13-00:24:20.490113 44c1e940 Compacting 5@1 + 281@2 files
> 2012/04/13-00:24:25.824995 44c1e940 Compacting 1@1 + 0@2 files
> 2012/04/13-00:24:26.008857 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:26.196877 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:26.312465 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:26.429817 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:26.533483 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:26.631044 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:26.733702 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:26.832787 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:26.949864 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:27.052502 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:27.164623 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:27.275621 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:27.376748 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:27.477728 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:27.611332 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:28.050275 44c1e940 Compacting 50@2 + 242@3 files
> 2012/04/13-00:24:32.455665 44c1e940 Compacting 1@2 + 0@3 files
> 2012/04/13-00:24:32.538566 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:32.819205 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:33.052064 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:33.198850 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:33.350893 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:33.521784 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:33.693531 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:33.847151 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:34.034277 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:34.225582 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:34.390228 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:34.554127 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:34.715242 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:34.852110 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:24:35.046899 44c1e940 Compacting 68@3 + 331@4 files
> 2012/04/13-00:25:02.582758 44c1e940 Compacting 433@3 + 2159@4 files
> 2012/04/13-00:26:39.827096 44c1e940 Compacting 1@3 + 0@4 files
> 2012/04/13-00:26:39.992623 44c1e940 Compacting 72@4 + 354@5 files
> 2012/04/13-00:27:13.024120 44c1e940 Compacting 9@4 + 51@5 files
> 2012/04/13-00:27:18.007566 44c1e940 Compacting 9@4 + 48@5 files
> 2012/04/13-00:27:23.026351 44c1e940 Compacting 8@4 + 41@5 files
> 2012/04/13-00:27:28.408619 44c1e940 Compacting 6@4 + 33@5 files
> 2012/04/13-00:27:32.522630 44c1e940 Compacting 6@4 + 32@5 files
> 2012/04/13-00:27:36.719610 44c1e940 Compacting 6@4 + 31@5 files
> 2012/04/13-00:27:41.277302 44c1e940 Compacting 6@4 + 33@5 files
> 2012/04/13-00:27:44.928451 44c1e940 Compacting 6@4 + 32@5 files
> 2012/04/13-00:27:48.168874 44c1e940 Compacting 6@4 + 34@5 files
> 2012/04/13-00:27:52.718402 44c1e940 Compacting 6@4 + 32@5 files
> 2012/04/13-00:27:55.665107 44c1e940 Compacting 6@4 + 33@5 files
> 2012/04/13-00:27:59.381808 44c1e940 Compacting 6@4 + 34@5 files
> 2012/04/13-00:28:03.592802 44c1e940 Compacting 6@4 + 33@5 files
> 2012/04/13-00:28:07.179032 44c1e940 Compacting 664@4 + 3330@5 files
> 2012/04/13-00:29:58.239662 44c1e940 Compacting 101@4 + 500@5 files
> 2012/04/13-00:30:22.333750 44c1e940 Compacting 1@4 + 0@5 files
> 2012/04/13-00:45:28.851715 44c1e940 Compacting 4@0 + 1@1 files
> 2012/04/13-01:00:31.152105 44c1e940 Compacting 4@0 + 3@1 files
> 2012/04/13-01:10:33.167940 44c1e940 Compacting 4@0 + 3@1 files
> 2012/04/13-01:25:35.113416 44c1e940 Compacting 4@0 + 3@1 files
> 2012/04/13-01:35:37.621499 44c1e940 Compacting 4@0 + 2@1 files
> [jsirois@smf1-ajb-35-sr1 ~]$ grep Compacting /var/lib/mesos/scheduler_db/mesos_log/LOG
> 2012/04/13-01:44:32.533694 44c27940 Compacting 2@0 + 3@1 files
> 2012/04/13-01:44:32.586958 44c27940 Compacting 2@1 + 6@2 files
> 2012/04/13-01:44:32.739514 44c27940 Compacting 1@2 + 0@3 files
> 2012/04/13-01:44:32.768764 44c27940 Compacting 1@2 + 0@3 files
> 2012/04/13-01:44:32.843866 44c27940 Compacting 1@3 + 0@4 files
> 2012/04/13-01:44:32.973304 44c27940 Compacting 1@3 + 0@4 files
> 2012/04/13-01:44:33.009686 44c27940 Compacting 1@4 + 2@5 files
> 2012/04/13-01:44:33.074056 44c27940 Compacting 1@4 + 0@5 files
> 2012/04/13-02:01:42.947456 44c27940 Compacting 4@0 + 1@1 files
> 2012/04/13-02:16:45.326088 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-02:31:48.360851 44c27940 Compacting 4@0 + 1@1 files
> 2012/04/13-02:41:50.055622 44c27940 Compacting 4@0 + 3@1 files
> 2012/04/13-02:51:51.889148 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-03:01:54.345784 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-03:11:55.987774 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-03:21:57.701121 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-03:31:59.373435 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-03:42:01.047061 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-03:52:03.088683 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-04:02:05.181165 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-04:12:06.757773 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-04:22:08.598259 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-04:32:10.882913 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-04:42:12.602192 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-04:52:14.779705 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-05:02:16.621063 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-05:12:18.608767 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-05:22:20.453201 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-05:32:22.215804 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-05:42:23.882423 44c27940 Compacting 4@0 + 4@1 files
> 2012/04/13-05:52:25.553032 44c27940 Compacting 4@0 + 4@1 files
> With the format: [number of sstables compacted]@[level #] this says all levels are compacted
on startup now, but once running we only see level0 -> level1 compactions and this accounts
for the observed space leak.



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