[jira] [Updated] (OAK-2654) SegmentIdTable too eager to refresh

["Alex Parvulescu (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/OAK-2654?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Alex Parvulescu updated OAK-2654:
---------------------------------
    Fix Version/s: 1.2
                   1.1.8

> SegmentIdTable too eager to refresh
> -----------------------------------
>
>                 Key: OAK-2654
>                 URL: https://issues.apache.org/jira/browse/OAK-2654
>             Project: Jackrabbit Oak
>          Issue Type: Improvement
>          Components: segmentmk
>            Reporter: Alex Parvulescu
>            Assignee: Alex Parvulescu
>             Fix For: 1.1.8, 1.2
>
>         Attachments: OAK-2654.patch
>
>
> Calling SegmentIdTable#getSegmentId might trigger a reference table refresh if a certain condition is met, I think that this condition is too eager to trigger the refresh and in high write scenarios, this results in large pauses as the method is synchronized.
> The current condition resembles a cache miss (_index != first_) which means that when looking up a segment id by the _lsb_ it might happen that it either 
>  - is not there, so it needs to be added (no refresh on this branch)
>  - or there is an overlap on lsb values (actually on the value returned by _getIndex(lsb)_), in which case a refresh will be triggered.
> In high write scenarios the refresh case happens a lot more frequently so a refresh is triggered, even if it might not be needed. a refresh makes sense when there are null references and it might make sense for them to be collected otherwise we're just creating clones of the same map over and over again.



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