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https://issues.apache.org/jira/browse/BOOKKEEPER-572?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13632698#comment-13632698
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Ivan Kelly commented on BOOKKEEPER-572:
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{quote}1), I don't think we really need write WAL first (since it still has the
problem I raised in previous comment).{quote}
This problem (assuming your referring to corrupt journal entry) is easily
handled the same way we handle it today. If LedgerStorage#addEntry throws an
IOException, send an error back to the client, if it throws a
NoWritableLedgerDirException, transition to read only mode [1]. Any other
exception would have to be a RuntimeException, and a RuntimeException indicates
a bug in our code, which we should directly fix. But in any case, the handling
of this is independent of whether we add to the ledger storage before or after
the journal.
I like the COW idea. This is effectively what the skiplists do. However, I
think we should continue to support interleaved and skiplist for the moment
anyhow.
[1] The current patch only handles the transition to read only case, I need to
add the IOException case which i'll do when BOOKKEEPER-564 is resolved.
> 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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