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https://issues.apache.org/jira/browse/BOOKKEEPER-572?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13627059#comment-13627059
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Flavio Junqueira commented on BOOKKEEPER-572:
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I guess I'm simply not entirely convinced by the description of this jira,
although I have a guess. It says that writing to the ledger device first is the
fundamental problem behind BOOKKEEPER-447 and blocks a nice solution to
BOOKKEEPER-530. I'm not sure why it blocks a nice solution to BOOKKEEPER-530,
but for 447, is the problem that we don't have control over the OS page cache,
so we don't really know when it is written back, and consequently we can't
coordinate with index flushing?
I'm getting this feeling that I have asked this question before...
> Make the journal a write ahead log
> ----------------------------------
>
> Key: BOOKKEEPER-572
> URL: https://issues.apache.org/jira/browse/BOOKKEEPER-572
> Project: Bookkeeper
> Issue Type: Bug
> Reporter: Ivan Kelly
> Assignee: Ivan Kelly
> Fix For: 4.3.0
>
> Attachments:
> 0001-BOOKKEEPER-572-Write-to-the-journal-before-writing-t.patch,
> 0001-BOOKKEEPER-572-Write-to-the-journal-before-writing-t.patch,
> 0001-BOOKKEEPER-572-Write-to-the-journal-before-writing-t.patch,
> 0001-BOOKKEEPER-572-Write-to-the-journal-before-writing-t.patch,
> 0003-BOOKKEEPER-572-Write-to-the-journal-before-writing-t.patch,
> 0003-BOOKKEEPER-572-Write-to-the-journal-before-writing-t.patch,
> BookieServer-2013-02-22.snapshot
>
>
> A bookie adds to the LedgerStorage before writing to the journal. This is the
> fundamental problem behind BOOKKEEPER-447 and blocks a nice solution to
> BOOKKEEPER-530. By writing to the memory state before the journal, we exposed
> ourselves to bugs if the bookie crashed before we wrote to the journal. The
> entry may exist in index, but not in the entrylog, a situation which cannot
> be distinguished from an I/O error. The comments on BOOKKEEPER-447 goes into
> more details.
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