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From stack <st...@duboce.net>
Subject Re: Sequence Number for Cache Flush
Date Tue, 03 Jun 2008 17:03:54 GMT
Does tupdatesLock prevent the hole you describe?  Flushing must hold the 
updatesLock write lock to proceed.  Updates take out a read lock on 
updatesLock.  All updates will have gone into the WAL and into the 
memcache before the read lock is released.

St.Ack


Ning Li wrote:
> Hi,
>
> I want to confirm this before opening an JIRA issue.
>
> An HRegion asks each HStore to flush its cache with a sequence number
> X. The assumption is that all the updates before X will be flushed. So
> during the startup reconstruction, the updates before X are skipped.
>
> However, the implementation does not guarantee that all the updates
> before X will be flushed when HStore flushes with X. This is because
> HRegion uses write-ahead logging and X is the latest sequence number.
> Some updates may not have been written to the cache which will be
> flushed.
>
> I'll open an JIRA issue once confirmed.
>
> Ning
>   


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