[Cassandra Wiki] Update of "FAQ" by BrandonWilliams

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The "FAQ" page has been changed by BrandonWilliams:
http://wiki.apache.org/cassandra/FAQ?action=diff&rev1=139&rev2=140

   * [[#schema_disagreement|What are schema disagreement errors and how do I fix them?]]
   * [[#dropped_messages|Why do I see "... messages dropped.." in the logs?]]
   * [[#cli_keys|Why does the 0.8 cli not assume keys are strings anymore?]]
+  * [[#memlock|Cassandra dies with "java.lang.OutOfMemoryError: Map failed"]]
  
  <<Anchor(cant_listen_on_ip_any)>>
  
@@ -541, +542 @@

  
  If all your keys are of the same type, you should add information to the CF metadata, e.g., "update column family <cf> with key_validation_class = 'UTF8Type'".  If you have heterogeneous keys, you can tell the cli what type to use on case-by-case basis, as in, "assume <cf> keys as utf8".
  
+ <<Anchor(memlock)>>
+ == Cassandra dies with "java.lang.OutOfMemoryError: Map failed" ==
+ '''IF''' Cassandra is dying specifically with the "Map failed" message it means the OS is denying java the ability to lock more memory.  In linux, this typically means memlock is limited.  Check /proc/<pid of cassandra>/limits to verify this and raise it (eg, via ulimit in bash.)  Note that the debian and redhat packages handle this for you automatically.
+