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From Placido Revilla <placido.revi...@gmail.com>
Subject Re: Sync latency
Date Mon, 09 Apr 2012 08:47:09 GMT
Sorry, that's not the problem. In my logs block reporting never takes more
than 50 ms to process, even when I'm experiencing sync pauses of 30 seconds.

The dataset is currently small (1.2 TB), as the cluster has been running
live for a couple of months only and I have only slightly over 11K blocks
in total, that's why block reporting takes little time.

On Thu, Apr 5, 2012 at 8:16 PM, Todd Lipcon <todd@cloudera.com> wrote:

> Hi Placido,
>
> Sounds like it might be related to HDFS-2379. Try updating to Hadoop
> 1.0.1 or CDH3u3 and you'll get a fix for that.
>
> You can verify by grepping for "BlockReport" in your DN logs - if the
> pauses on the hbase side correlate with long block reports on the DNs,
> the upgrade should fix it.
>
> -Todd
>
> On Wed, Apr 4, 2012 at 2:30 AM, Placido Revilla
> <placido.revilla@gmail.com> wrote:
> > Hi,
> >
> > I'm having a problem with sync latency on our HBase cluster. Our cluster
> is
> > composed of 2 NN (and HBase master) machines and 12 DN (and HBase
> > regionservers and thrift servers). We are having several issues a day
> where
> > the cluster seems to halt all processing during several seconds, and
> these
> > times are aligned with some WARN logs:
> >
> > 13:23:55,285 WARN  [IPC Server handler 62 on 60020] wal.HLog IPC Server
> > handler 62 on 60020 took 10713 ms appending an edit to hlog;
> > editcount=150694, len~=58.0
> > 13:23:55,286 WARN  [IPC Server handler 64 on 60020] wal.HLog IPC Server
> > handler 64 on 60020 took 10726 ms appending an edit to hlog;
> > editcount=319217, len~=47.0
> > 13:23:55,286 WARN  [IPC Server handler 118 on 60020] wal.HLog IPC Server
> > handler 118 on 60020 took 10741 ms appending an edit to hlog;
> > editcount=373337, len~=49.0
> > 13:23:55,286 WARN  [IPC Server handler 113 on 60020] wal.HLog IPC Server
> > handler 113 on 60020 took 10746 ms appending an edit to hlog;
> > editcount=57912, len~=45.0
> > 15:39:38,193 WARN  [IPC Server handler 94 on 60020] wal.HLog IPC Server
> > handler 94 on 60020 took 21787 ms appending an edit to hlog;
> > editcount=2901, len~=45.0
> > 15:39:38,194 WARN  [IPC Server handler 82 on 60020] wal.HLog IPC Server
> > handler 82 on 60020 took 21784 ms appending an edit to hlog;
> > editcount=29944, len~=46.0
> > 16:09:38,201 WARN  [IPC Server handler 78 on 60020] wal.HLog IPC Server
> > handler 78 on 60020 took 10321 ms appending an edit to hlog;
> > editcount=163998, len~=104.0
> > 16:09:38,203 WARN  [IPC Server handler 97 on 60020] wal.HLog IPC Server
> > handler 97 on 60020 took 10205 ms appending an edit to hlog;
> > editcount=149497, len~=60.0
> > 16:09:38,203 WARN  [IPC Server handler 68 on 60020] wal.HLog IPC Server
> > handler 68 on 60020 took 10199 ms appending an edit to hlog;
> > editcount=318268, len~=63.0
> > 16:09:38,203 WARN  [IPC Server handler 120 on 60020] wal.HLog IPC Server
> > handler 120 on 60020 took 10211 ms appending an edit to hlog;
> > editcount=88001, len~=45.0
> > 16:09:38,204 WARN  [IPC Server handler 88 on 60020] wal.HLog IPC Server
> > handler 88 on 60020 took 10235 ms appending an edit to hlog;
> > editcount=141516, len~=100.0
> >
> > The machines in the cluster are pretty powerful (8 HT cores, 48 GB RAM, 6
> > SATA 7200 RPM disks) so we are not peaking on any hardware, for example
> CPU
> > is never over 20% used (avg 5%), network BW is never over 100 Mbps (with
> 1
> > Gbps links) and 10k packets/s in each RS, RAM is 50% free (used for disk
> > cache) and random IOPS is well under 120 per sec (we should be able to
> > stand over 600). We have also monitored the GC for pauses (we have 16GB
> of
> > heap for the region servers) and we don't see pauses of more than a
> couple
> > tens of milliseconds (and concurrent sweeps of more than 5 or 6 seconds).
> >
> > The cluster runs Hadoop 1.0.0 and HBase 0.90.5 almost vanilla (just a
> > couple of functionality patches) and the input channel is thrift, with
> > autocommit disabled and periodic client flushes every 5 seconds. Our
> tables
> > have the deferred log flush feature enabled with a optional interval of
> > 1000 ms. We are not doing any MapReduce on this cluster, just HBase
> > concurrent writes and reads on three tables, two of them with 64 regions
> > and one with 1024 (a little bit high, I know) and an almost perfectly
> > random spread of keys throughout all the cluster. With this setup we are
> > able to see a peak of 250k requests/s (about 22k request per RS) with an
> > average of 100k request/s a day and an average of 76 bytes per request
> (so,
> > about 150 Mbps in throughput), because our payload is pretty small (less
> > than 20 bytes).
> >
> > The thrift servers are doing about 250 multi operations per second in
> each
> > RS, sustained (on peaks it is just packing more requests in each
> operation).
> >
> > So, the cluster is performing well on average, but these pauses are
> killing
> > us (they last up to 30 seconds on bursts of up to 3 minutes). Does anyone
> > have a clue as to what could be happening?
> >
> > Thanks.
>
>
>
> --
> Todd Lipcon
> Software Engineer, Cloudera
>

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