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https://issues.apache.org/jira/browse/BOOKKEEPER-447?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13498139#comment-13498139
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Yixue (Andrew) Zhu commented on BOOKKEEPER-447:
-----------------------------------------------

HI Ivan,

I have a patch for BOOKKEEPER-432 rolled out internally, will post it shortly.
After some benchmark, we decided not go with Aniruddha's approach.

I will also creates a separate jira to eliminate/reduce on-disk index (my 
original proposal to BOOKKEEPER-432), as it hurt sync/write through put. 
Suppose there are thousands of ledgers per bookie, sync potentially needs to 
flush thousands of index files.
  
 

                
> 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, 4.1.1
>
>         Attachments: BOOKKEEPER-447.diff
>
>
> 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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