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From Apache Wiki <>
Subject [Cassandra Wiki] Update of "MemtableThresholds" by EricEvans
Date Wed, 13 May 2009 21:19:54 GMT
Dear Wiki user,

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The following page has been changed by EricEvans:

The comment on the change is:
saving work in progress

  in check, and memory usage in general with limits.
  == MemtableSizeInMB ==
+ FIXME: finish this section!
  == MemtableObjectCountInMillions ==
+ FIXME: finish this section!
  == Using Jconsole To Optimize Thresholds ==
  Cassandra's column-family mbeans have a number of attributes that can
@@ -24, +26 @@

  you will need to connect remotely (the default startup scripts for
  Cassandra cause the VM to listen on port 8080).
- [connect.png]
+ attachment:jconsole_connect.png
- Once connected, select the ''MBeans'' tab, expand the ''org.apache.cassandra.db''
+ Once connected, select the ''MBeans'' tab, expand the 
- section, and finally one of your column families.
+ ''org.apache.cassandra.db'' section, and finally one of your column families.
- The interesting attributes here are:
+ There are three interesting attributes here.
-  * ''!MemtableColumnsCount:''
-  * ''!MemtableDataSize:''
-  * ''!MemtableSwitchCount:''
+  1. ''!MemtableColumnsCount'', representing the total number of column entries in this table.
If you store 100 rows that each have 100 columns, expect to see this value increase by 10,000.
+  1. ''!MemtableDataSize'', which is used to determine the total size of stored data. This
is the sum of all the values stored and does not account for Memtable overhead, (i.e. it's
not indicative of the actual memory used by the Memtable).
+  1. Finally there is ''!MemtableSwitchCount'' which increases by one each time a column
family flushes its Memtable to disk.
- [attributes.png]
+ ''Note: You'll need to manually mash the `Refresh` button to update the values.''
- [operations.png]
+ attachment:jconsole_attributes.png
+ It is also possible to schedule an immediate flush using the `forceFlush()` operation.
+ attachment:jconsole_operations.png

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