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From Stephen Henderson <>
Subject memory_locking_policy parameter in cassandra.yaml for disabling swap - has this variable been renamed?
Date Thu, 28 Jul 2011 10:17:10 GMT

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:
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


Stephen Henderson - Lead Developer (Onsite), Cognitive Match<> |<>
T: +44 (0) 203 205 0004 | F: +44 (0) 207 526 2226

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