[jira] [Commented] (OAK-4732) (Slightly) prioritise reads over writes

["Michael Dürig (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-4732?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16074435#comment-16074435 ] 

Michael Dürig commented on OAK-4732:
------------------------------------

Patch looks good to me. Maybe we increase the {{SynchronizedDescriptiveStatistics}} window a bit? 1000 instead of 100? 

As a follow up, it would be good to add a feature flag to control this feature if this turns out to be necessary. One way would be to add a flag to configure the percentile used in {{LockBasedScheduler.getHeadNodeState()}}. Setting it to {{0}} would basically disable this. Setting it to a different value might be interesting in future experiments. 

> (Slightly) prioritise reads over writes 
> ----------------------------------------
>
>                 Key: OAK-4732
>                 URL: https://issues.apache.org/jira/browse/OAK-4732
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: segment-tar
>            Reporter: Michael Dürig
>            Assignee: Andrei Dulceanu
>            Priority: Minor
>              Labels: Performance, scalability
>             Fix For: 1.8, 1.7.4
>
>         Attachments: OAK-4732.patch
>
>
> When fetching the current root from the {{SegmentNodeStore}} an older revision will be returned when a commit is being processed concurrently. I think it would make sense to wait for a short time in this case increasing the chance of returning an up to date state. The idea is that this would lower the rebasing work that need to be done later on should the returned root be used for further modifications. 
> An interesting value for the wait time is to use  the median (or more general a percentile) of the commit time of the last say 1000 commits. This would mean that (for the median) we have a 50% chance of getting up to date date. For a 90% percentile we would have longer wait times but then a 90% chance of getting up to date date. 



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