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From lars hofhansl <la...@apache.org>
Subject Re: Disk space leak when using HBase and HDFS ShortCircuit
Date Fri, 27 Jun 2014 21:31:28 GMT
Sounds scary!
HDP 2.1 ships with Hadoop 2.4.0, right?


Sounds like a serious HDFS bug with SSR.
Maybe we need to at least document this behavior and recommend settings in the HBase book.

-- Lars


----- Original Message -----
From: Giuseppe Reina <g.reina@gmail.com>
To: user@hbase.apache.org
Cc: 
Sent: Wednesday, June 25, 2014 2:54 AM
Subject: Disk space leak when using HBase and HDFS ShortCircuit

Hi all,
   we have been experiencing the same problem with 2 of our clusters. We
are currently using HDP 2.1 that comes with HBase 0.98.

The problem manifested by showing a huge differences (hundreds of GB)
between the output of "df" and "du" of the hdfs data directories.
Eventually, other systems complained for the lack of space before shutting
down. We identified the problem and discovered that all the RegionServers
were holding lots of open file descriptors to deleted files, which
prevented the OS to free the disk space occupied (hence the difference
between "df" and "du"). The deleted files were pointing to the local HDFS
blocks of old HFiles deleted from HDFS during the compaction and/or split
operations. Apparently those file descriptors were stored by the HDFS
ShortCircuit cache.

My question is, isn't the shortcircuit feautre supposed to get "notified"
somehow of file deletion on a file on HDFS so it can remove the open fds
from the cache? This creates huge leaks whenever HBase is heavily loaded
and we had to restart the RegionServer periodically until before
identifying the problem. We solved the problem first by disabling
shortcircuit from HDFS and then enabling it and reducing the cache size so
to trigger often the caching policies (this leads to some performance
loss).


p.s. I am aware of the "dfs.client.read.shortcircuit.streams.cache.expiry.ms
" directoparameter, but for some reason the default value (5 mins) does not
work out-of-the-box on HDP 2.1, moreover the problem persists for high
timeouts and big cache sizes.

Kind Regards


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