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From Apache Wiki <wikidi...@apache.org>
Subject [Cassandra Wiki] Trivial Update of "Counters" by SylvainLebresne
Date Wed, 30 Nov 2011 08:39:56 GMT
Dear Wiki user,

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

The "Counters" page has been changed by SylvainLebresne:
http://wiki.apache.org/cassandra/Counters?action=diff&rev1=15&rev2=16

  == Technical limitations ==
  
    * If a write fails unexpectedly (timeout or loss of connection to the coordinator node)
the client will not know if the operation has been performed. A retry can result in an over
count [[https://issues.apache.org/jira/browse/CASSANDRA-2495|CASSANDRA-2495]].
-   * Counter removal is intrinsically limited. For instance, if you issue very quickly the
sequence "increment, remove, increment" it is possible for the removal to be lost (if for
some reason the remove happens to be the last received messages). Hence, removal of counters
is provided for definitive removal only, that is when the deleted counter is not increment
afterwards. Note that if you need to reset a counter, you can read its ''value'' and insert
''-value''. 
+   * Counter removal is intrinsically limited. For instance, if you issue very quickly the
sequence "increment, remove, increment" it is possible for the removal to be lost (if for
some reason the remove happens to be the last received messages). Hence, removal of counters
is provided for definitive removal only, that is when the deleted counter is not increment
afterwards. This holds for row deletion too: if you delete a row of counters, incrementing
any counter in that row (that existed before the deletion) will result in an undetermined
behavior. Note that if you need to reset a counter, one option (that is unfortunately not
concurrent safe) could be to read its ''value'' and insert ''-value''.
    * `CounterColumnType` may only be set in the `default_validation_class`. A column family
either contains only counters, or no counters at all.
  
  == Further reading ==

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