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Date: Fri, 29 Jul 2011 13:13:02 +1200
From: Teijo Holzer <tholzer@wetafx.co.nz>
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To: user@cassandra.apache.org
CC: Stephen Henderson <stephen.henderson@cognitivematch.com>
Subject: Re: memory_locking_policy parameter in cassandra.yaml for disabling
 swap - has this variable been renamed?
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Hi,

yes I was looking for this config as well.

This is really simple to achieve:

Put the following line into /etc/security/limits.conf

cassandra        -       memlock         32

Then, start Cassandra as the user cassandra, not as root (note there is never a 
need to run Cassandra as root, all functionality can be achieved from a normal 
user by changing the right configs).

In the log you will see:

[2011-07-29 13:06:46,491] WARN: Unable to lock JVM memory (ENOMEM). This can 
result in part of the JVM being swapped out, especially with mmapped I/O 
enabled. Increase RLIMIT_MEMLOCK or run Cassandra as root. (main CLibrary.java:118)

Done.

If you want enable mlockall again, simply change the above 32(k) value to the 
size of your RAM (e.g. 17825792 for a 16GB machine).

We also have turned off mmap altogether and never had any memory issues again. 
swap is happily enabled. We currently prefer stability over performance.

Cheers,

	T.

On 28/07/11 22:17, Stephen Henderson wrote:
> Hi,
>
> We�ve started having problems with cassandra and memory swapping on linux which
> seems to be a fairly common issue (in our particular case after about a week
> all swap space will have been used up and we have to restart the process).
>
> It sounds like the general consensus is to just disable swap completely, but
> the recently released �Cassandra High Performance Cookbook� from Packt has
> instructions for �Stopping cassandra from using swap without disabling it
> system wide�. We�ve tried following the instructions but it refers to a
> �memory_locking_policy� variable in cassandra.yaml which throws an �unknown
> property� error on startup and I can�t find any reference to it in any of the
> cassandra docs.
>
> I�ve copied the summarised instructions below, does anyone know if this is
> something that ever worked or is there a different variable to set which does
> the same thing? (we�re using 0.7.4 at present and it looks like the book was
> written for 0.7.0-beta-1.10 so it might have been something which was abandoned
> during beta?)
>
> ---
>
> Disabling Swap Memory system-wide may not always be desirable. For example, if
> the system is not dedicated to running Cassandra, other processes on the system
> may benefit from Swap Memory. This recipe shows how to install the Java Native
> Architecture, which allows Java to lock itself in memory making it inevitable.
>
> 1. Place the jna.jar and platform.jar in the $CASSANDRA_HOME/lib directory:
>
> 2. Enable memory_locking_policy in $CASSANDRA_HOME/conf/cassandra.yaml:
> �memory_locking_policy: required�
>
> 3. Restart your Cassandra instance.
>
> 4. Confirm this configuration has taken effect by checking to see if a large
> portion of memory is Unevictable:
>
> $ grep Unevictable /proc/meminfo
>
> Unevictable: 1024 Kb
>
> ---
>
> Thanks,
>
> Stephen
>
> *Stephen Henderson � *Lead Developer (Onsite), Cognitive Match
>
> stephen.henderson@cognitivematch.com
> <mailto:stephen.henderson@cognitivematch.com> | http://www.cognitivematch.com
> <http://www.cognitivematch.com/>
>
> T: +44 (0) 203 205 0004 | F: +44 (0) 207 526 2226
>