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https://issues.apache.org/jira/browse/OAK-4097?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15383749#comment-15383749
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Andrei Dulceanu commented on OAK-4097:
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I'd like some advice regarding how to approach this issue. One way would be to
add a {{{FileStoreMonitor}}} instance variable in {{{TarRevisions}}} and have a
new {{{FileStoreMonitor::flushed()}}} method being called at each
{{{TarRevisions::flush()}}} invocation. IMO this would satisfy the requirement,
since {{{TarRevisions::flush()}}} is the only place where a journal write
happens.
On the other hand, as suggested by [~frm], we could intercept calls to
{{{org.apache.jackrabbit.oak.segment.WriteOperationHandler::flush()}}} "since
this method guarantees that pending changes in in-memory segments are persisted
on disk via a write." I think this is a more general approach, but since
{{{WriteOperationHandler::flush()}}} is called in {{{SegmentWriter::flush()}}}
which in turn is called in numerous places (including {{{FileStore::flush()}}}
which causes also the journal write), without necessarily modifying the journal
file, I'd assume the metric collected would be one related to {{{FileStore}}}
writes, not to journal writes.
Any ideas on how to move this forward?
> Add metric for FileStore journal writes
> ---------------------------------------
>
> Key: OAK-4097
> URL: https://issues.apache.org/jira/browse/OAK-4097
> Project: Jackrabbit Oak
> Issue Type: Improvement
> Components: segment-tar
> Reporter: Chetan Mehrotra
> Assignee: Andrei Dulceanu
> Priority: Minor
> Fix For: 1.6, Segment Tar 0.0.6
>
>
> TarMK flush thread should run every 5 secs and flush the current root head to
> journal.log. It would be good to have a metric to capture the number of runs
> per minute
> This would help in confirming if flush is working at expected frequency or
> delay in acquiring locks is causing some delays
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