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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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Michael Dürig edited comment on OAK-4097 at 7/19/16 9:24 AM:
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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?
was (Author: dulceanu):
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 {{FileStor}}}
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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