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From Apache Wiki <wikidi...@apache.org>
Subject [Cassandra Wiki] Update of "MemtableThresholds" by MakiWatanabe
Date Fri, 11 Mar 2011 15:09:30 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Cassandra Wiki" for change notification.

The "MemtableThresholds" page has been changed by MakiWatanabe.
The comment on this change is: Update threashold names in Jconsole description.
http://wiki.apache.org/cassandra/MemtableThresholds?action=diff&rev1=20&rev2=21

--------------------------------------------------

  
  '''Larger memtables do lead to more effective compaction''': Since compaction is tiered,
large sstables are preferable: turning over tons of tiny memtables is bad. Again, this impacts
read performance (by improving the overall io-contention weather), but not writes.
  
- Listed below are the thresholds found in `storage-conf.xml`, along with a description.
+ Listed below are the thresholds found in `storage-conf.xml` (or `cassandra.yaml` in 0.7+),
along with a description.
  
  === MemtableThroughputInMB ===
  As the name indicates, this sets the max size in megabytes that the  Memtable will store
before triggering a threshold violation and causing it to be flushed to disk. It corresponds
to the size of the values inserted, (plus the size of the containing column).
@@ -64, +64 @@

  
  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.
This attribute is useful in setting the [[#MemtableObjectCountInMillions|MemtableObjectCountInMillions]]
threshold.
+  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 [[#MemtableOperationsInMillions|MemtableOperationsInMillions]]
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). Use this value when adjusting [[#MemtableSizeInMB|MemtableSizeInMB]].
+  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 [[#MemtableThroughputInMB|MemtableThroughputInMB]].
   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 these values.''

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