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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