[jira] [Comment Edited] (OAK-4097) Add metric for FileStore journal writes

["Andrei Dulceanu (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-4097?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15383749#comment-15383749 ] 

Andrei Dulceanu edited comment on OAK-4097 at 7/19/16 7:58 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 {{FileStor}}} 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 {{{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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