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From Dhruba Borthakur <dhr...@gmail.com>
Subject Re: performance: HLog flush to disk each thread, can we decrease IO calls?
Date Wed, 29 Jun 2011 13:14:04 GMT
We have implemented this idea, and it definitely increases HLog performance
by quite a large number. The one drawabck is that writes to HLog (from HDFS
perspective) become more "batchy", and writes to a HDFS file consume quite a
bit of CPU. So I have observed that this change increase overall system
throughput, but suffer slightly on individual transaction latency.


On Wed, Jun 29, 2011 at 6:08 AM, Joey Echeverria <joey@cloudera.com> wrote:

> Hey Mingjian,
> This sounds like a good idea  Your patch didn't make it through. Would you
> mind either filing a JIRA and uploading your patch there or at least posting
> it to something like pastebin so we can take a look.
> -Joey
> On Jun 29, 2011, at 3:27, Mingjian Deng <koven2049@gmail.com> wrote:
> > Hi:
> >     We found that the hlog sync to disk each time. When one thread exec
> "doWrite(info, logKey, edit);", the others wait for "updateLock" in
> HLog.java.
> >     Why not the others add their edits into a list and wait. When sync's
> time, the whole list sync to disk once. I think it will decrease the IO
> calls.
> >
> >     So Maybe we will make two lists for edits. Each thread write to the
> "waledits" and wait for "updateLock". Each thread can copy the "waledits" to
> "flushedits" and flush the "flushedits" to
> > disk once it gets "updateLock".
> >
> >     In my test, it can increase the write speed of 40%.
> >
> >     Just see the HLog.patch.
> >

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