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From Jean-Daniel Cryans <jdcry...@apache.org>
Subject Re: commit semantics
Date Tue, 12 Jan 2010 00:03:49 GMT
Hey Joydeep,

This is actually intended this way but the name of the variable is
misleading. The sync is done only if forceSync or we have enough
entries to sync (default is 1). If someone wants to sync only 100
entries for example, they would play with that configuration.

Hope that helps,

J-D

On Mon, Jan 11, 2010 at 3:46 PM, Joydeep Sarma <jssarma@apache.org> wrote:
> Hey HBase-devs,
>
> we have been going through hbase code to come up to speed.
>
> One of the questions was regarding the commit semantics. Thumbing through
> the RegionServer code that's appending to the wal:
>
> syncWal -> HLog.sync -> addToSyncQueue ->syncDone.await()
>
> and the log writer thread calls:
>
> hflush(), syncDone.signalAll()
>
> however hflush doesn't necessarily call a sync on the underlying log file:
>
>      if (this.forceSync ||
>          this.unflushedEntries.get() >= this.flushlogentries) { ... sync()
> ... }
>
> so it seems that if forceSync is not true, the syncWal can unblock before a
> sync is called (and forcesync seems to be only true for metaregion()).
>
> are we missing something - or is there a bug here (the signalAll should be
> conditional on hflush having actually flushed something).
>
> thanks,
>
> Joydeep
>

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