[jira] [Created] (OAK-1926) UnmergedBranch state growing with empty BranchCommit leading to performance degradation

["Chetan Mehrotra (JIRA)" <ji...@apache.org>]

Chetan Mehrotra created OAK-1926:
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             Summary: UnmergedBranch state growing with empty BranchCommit leading to performance degradation
                 Key: OAK-1926
                 URL: https://issues.apache.org/jira/browse/OAK-1926
             Project: Jackrabbit Oak
          Issue Type: Bug
          Components: mongomk
    Affects Versions: 1.0.1
            Reporter: Chetan Mehrotra
            Assignee: Chetan Mehrotra
             Fix For: 1.0.2, 1.1


In some cluster deployment cases it has been seen that in memory state of UnmergedBranches contains large number of empty commits. For e.g. in  one of of the runs there were 750 entries in the UnmergedBranches and each Branch had empty branch commits.

If there are large number of UnmergedBranches then read performance would degrade as for determining revision validity currently logic scans all branches

Below is some part of UnmergedBranch state

{noformat}
Branch 1
1 -> br146d2edb7a7-0-1 (true) (revision: "br146d2edb7a7-0-1", clusterId: 1, time: "2014-06-25 05:08:52.903", branch: true)
2 -> br146d2f0450b-0-1 (true) (revision: "br146d2f0450b-0-1", clusterId: 1, time: "2014-06-25 05:11:40.171", branch: true)
Branch 2
1 -> br146d2ef1d08-0-1 (true) (revision: "br146d2ef1d08-0-1", clusterId: 1, time: "2014-06-25 05:10:24.392", branch: true)
Branch 3
1 -> br146d2ed26ca-0-1 (true) (revision: "br146d2ed26ca-0-1", clusterId: 1, time: "2014-06-25 05:08:15.818", branch: true)
2 -> br146d2edfd0e-0-1 (true) (revision: "br146d2edfd0e-0-1", clusterId: 1, time: "2014-06-25 05:09:10.670", branch: true)
Branch 4
1 -> br146d2ecd85b-0-1 (true) (revision: "br146d2ecd85b-0-1", clusterId: 1, time: "2014-06-25 05:07:55.739", branch: true)
Branch 5
1 -> br146d2ec21a0-0-1 (true) (revision: "br146d2ec21a0-0-1", clusterId: 1, time: "2014-06-25 05:07:08.960", branch: true)
2 -> br146d2ec8eca-0-1 (true) (revision: "br146d2ec8eca-0-1", clusterId: 1, time: "2014-06-25 05:07:36.906", branch: true)
Branch 6
1 -> br146d2eaf159-1-1 (true) (revision: "br146d2eaf159-1-1", clusterId: 1, time: "2014-06-25 05:05:51.065", counter: 1, branch: true)
Branch 7
1 -> br146d2e9a513-0-1 (true) (revision: "br146d2e9a513-0-1", clusterId: 1, time: "2014-06-25 05:04:26.003", branch: true)
{noformat}

[~mreutegg] Suggested that these branch might be for those revision which have resulted in a collision and upon checking it indeed appears to be the case  (value true in brackets above indicate that). Further given the age of such revision it looks like they get populated upon startup itself

*Fix*
* Need to check why we need to populate the UnermgedBranch
* Possibly implement some purge job which would remove such stale entries 





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