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From: Apache Wiki <wikidiffs@apache.org>
To: Apache Wiki <wikidiffs@apache.org>
Date: Tue, 19 Jul 2011 20:18:45 -0000
Message-ID: <20110719201845.41039.80699@eos.apache.org>
Subject: =?utf-8?q?=5BCassandra_Wiki=5D_Update_of_=22FAQ=22_by_thepaul?=
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Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Cassandra Wiki" for=
 change notification.

The "FAQ" page has been changed by thepaul:
http://wiki.apache.org/cassandra/FAQ?action=3Ddiff&rev1=3D123&rev2=3D124

Comment:
document what i've found about ubuntu/ec2/jna/memlock "task blocked for mor=
e than 120 seconds" problems

   * [[#seed_spof|Does single seed mean single point of failure?]]
   * [[#jconsole_array_arg|Why can't I call jmx method X on jconsole? (ex. =
getNaturalEndpoints)]]
   * [[#max_key_size|What's the maximum key size permitted?]]
+  * [[#ubuntu_ec2_hangs|I'm using Ubuntu on EC2 with JNA, and holy crap we=
ird things keep hanging and stalling and printing scary tracebacks in dmesg=
!]]
  =

  <<Anchor(cant_listen_on_ip_any)>>
  =

@@ -476, +477 @@

  =

  Routing is O(N) of the key size and querying and updating are O(N log N).=
 In practice these factors are usually dwarfed by other overhead, but some =
users with very large "natural" keys use their hashes instead to cut down t=
he size.
  =

+ <<Anchor(ubuntu_ec2_hangs)>>
+ =

+ =3D=3D I'm using Ubuntu on EC2 with JNA, and holy crap weird things keep =
hanging and stalling and blocking and printing scary tracebacks in dmesg! =
=3D=3D
+ =

+ We have come across several different, but similar, sets of symptoms that=
 might match what you're seeing. They might all have the same root cause; i=
t's not clear. One common piece is messages like this in dmesg:
+ =

+ {{{
+ INFO: task (some_taskname):(some_pid) blocked for more than 120 seconds.
+ "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
+ }}}
+ =

+ It does not seem that anyone has had the time to track this down to the r=
eal root cause, but it does seem that upgrading the linux-image-virtual pac=
kage and rebooting your instances fixes it. There is likely some bug in sev=
eral of the virtual/xen kernel builds distributed by Ubuntu which is fixed =
in later versions. Versions of linux-image-*-virtual which are known not to=
 have this problem include:
+ =

+  * linux-image-2.6.38-10-virtual (2.6.38-10.46) (Ubuntu 11.04/Natty Narwh=
al)
+  * linux-image-2.6.35-24-virtual (2.6.35-24.42) (Ubuntu 10.10/Maverick Me=
erkat)
+ =

+ Uninstalling libjna-java or recompiling Cassandra with CLibrary.tryMlocka=
ll()'s mlockall() call commented out also make at least some sorts of this =
problem go away, but that's a lot less desirable of a fix.
+ =

+ If you have more information on the problem and better ways to avoid it, =
please do update this space.
+=20