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HDFS >> mail # dev >> Fwd: Disk space leak when using HBase and HDFS ShortCircuit


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Fwd: Disk space leak when using HBase and HDFS ShortCircuit
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From: Vladimir Rodionov <[EMAIL PROTECTED]>
Date: Wed, Jun 25, 2014 at 12:03 PM
Subject: RE: Disk space leak when using HBase and HDFS ShortCircuit
To: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]>

As far as I understand this is issue of HDFS shorty-circuit-reads
implementation not HBase. HBase uses HDFS API to access
files. Did you ask this question on hdfs dev list? This looks like a very
serious bug.

Best regards,
Vladimir Rodionov
Principal Platform Engineer
Carrier IQ, www.carrieriq.com
e-mail: [EMAIL PROTECTED]

________________________________________
From: Giuseppe Reina [[EMAIL PROTECTED]]
Sent: Wednesday, June 25, 2014 2:54 AM
To: [EMAIL PROTECTED]
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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Best regards,

   - Andy

Problems worthy of attack prove their worth by hitting back. - Piet Hein
(via Tom White)