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From Apache Wiki <wikidi...@apache.org>
Subject [Cassandra Wiki] Update of "MemtableThresholds" by EricEvans
Date Wed, 13 May 2009 22:34:40 GMT
Dear Wiki user,

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The following page has been changed by EricEvans:
http://wiki.apache.org/cassandra/MemtableThresholds

The comment on the change is:
fleshed out a bit more of the jconsole section

------------------------------------------------------------------------------
  When performing write operations, Cassandra stores values to column-family
  specific, in-memory data structures, called Memtables. Memtables
  are flused to disk whenever a threshold is exceeded, so it's important to
- have these thresholds configured properly configured to keep Memtable size
+ have these thresholds configured properly to keep Memtable size
- in check, and memory usage in general with limits.
+ in check, and overall memory usage within limits.
  
  == MemtableSizeInMB ==
- FIXME: finish this section!
+ If left unset, defaults to 128MB.
  
  == MemtableObjectCountInMillions ==
- FIXME: finish this section!
+ If left unset, defaults to 1, (or 1,000,000 objects).
  
  == Using Jconsole To Optimize Thresholds ==
  Cassandra's column-family mbeans have a number of attributes that can
@@ -33, +33 @@

  
  There are three interesting attributes here.
  
-  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. ''!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.
This attribute is useful in setting the [#MemtableObjectCountInMillions MemtableObjectCountInMillions]
threshold.
-  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. ''!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). Use this value when adjusting [#MemtableSizeInMB
MemtableSizeInMB].
   1. Finally there is ''!MemtableSwitchCount'' which increases by one each time a column
family flushes its Memtable to disk.
  
  ''Note: You'll need to manually mash the `Refresh` button to update the values.''

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