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https://issues.apache.org/jira/browse/BOOKKEEPER-447?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13487201#comment-13487201
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Flavio Junqueira commented on BOOKKEEPER-447:
---------------------------------------------
Thanks for the feedback, Robin. Here is a another thought. In the case we end
up writing to the ledger device before we write to the journal, as you report
here, it is a problem if we have a pointer in the index of a ledger to an
entry, but the entry doesn't exist. It shouldn't be a problem, however, to have
an entry in the entry log, but not a pointer in the index. If you agree, then
what if we simply flush the entry log before we flush the ledger cache in
InterleavedLedgerStorage flush? we already write in the opposite order in
InterleavedLedgerStorage.addEntry.
> Bookie can fail to recover if index pages flushed before ledger flush
> acknowledged
> ----------------------------------------------------------------------------------
>
> Key: BOOKKEEPER-447
> URL: https://issues.apache.org/jira/browse/BOOKKEEPER-447
> Project: Bookkeeper
> Issue Type: Bug
> Components: bookkeeper-server
> Affects Versions: 4.2.0
> Reporter: Yixue (Andrew) Zhu
> Assignee: Robin Dhamankar
> Labels: patch
> Fix For: 4.2.0
>
>
> Bookie index page steal (LedgerCacheImpl::grabCleanPage) can cause index file
> to reflect unacknowledged entries (due to flushLedger). Suppose ledger and
> entry fail to flush due to Bookkeeper server crash, it will cause ledger
> recovery not able to use the bookie afterward, due to
> InterleavedStorageLedger::getEntry throws IOException.
> If the ackSet bookies all experience this problem (DC environment), the
> ledger will not be able to recover.
> The problem here essentially a violation of WAL. One reasonable fix is to
> track ledger flush progress (either per-ledger entry, or per-topic message).
> Do not flush index pages which tracks entries whose ledger (log) has not been
> flushed.
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