[Cassandra Wiki] Update of "Counters" by SylvainLebresne

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The "Counters" page has been changed by SylvainLebresne.
http://wiki.apache.org/cassandra/Counters?action=diff&rev1=9&rev2=10

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

  == Interface ==
  
  The interface follows the main API.  The main differences are:
-  * CounterColumn requires an i64 value and no timestamp, and
+  * CounterColumn requires an i64 value (can be negative) and no timestamp, and
-  * CounterDeletion does not take a timestamp.
+  * Deletion, when used on a counter column family, does not use a timestamp.
  Internally, the data store generates timestamps on the server to determine priority of deletion.
  
+ The new structures for dealing with counters are:
  {{{
  struct CounterColumn {
      1: required binary name,
@@ -53, +54 @@

      1: required binary name,
      2: required list<CounterColumn> columns
  }
- }}}
  
- {{{
  struct Counter {
      1: optional CounterColumn column,
      2: optional CounterSuperColumn super_column
  }
+ }}}
+ Moreover, as mentioned previously, then timestamp field of Deletion is now optional (but
+ remain mandatory for non counter column family operation).
  
+ The Mutation has also been updated with a new `counter` field for batch increment/decrement.
- struct CounterDeletion {
-     1: optional binary super_column,
-     2: optional SlicePredicate predicate,
- }
  
+ The counter operation comprise `batch_mutate` and the following new operations:
- /**
-     A CounterMutation is either an insert, represented by filling counter, or a deletion, represented by filling the deletion attribute.
-     @param counter. An insert to a counter column or supercolumn
-     @param deletion. A deletion of a counter column or supercolumn
- */
- struct CounterMutation {
-     1: optional Counter counter,
-     2: optional CounterDeletion deletion,
- }
- }}}
- 
  {{{
    # counter methods
  
@@ -87, +76 @@

             2:required ColumnParent column_parent,
             3:required CounterColumn column,
             4:required ConsistencyLevel consistency_level=ConsistencyLevel.ONE)
-        throws (1:InvalidRequestException ire, 2:UnavailableException ue, 3:TimedOutException te),
-   /**
-    * Batch increment or decrement a counter.
-    */
-   void batch_add(1:required map<binary, map<string, list<CounterMutation>>> update_map,
-                  2:required ConsistencyLevel consistency_level=ConsistencyLevel.ONE)
         throws (1:InvalidRequestException ire, 2:UnavailableException ue, 3:TimedOutException te),
  
    /**
@@ -132, +115 @@

  
  == Technical limitations ==
  
- Writes require CL.ONE.
-   * The commutative design requires partitionability and idempotence between partitions.
-   * If a write fails unexpectedly (timeout for example) the client will not know if the operation has been performed. A retry can result in an over count.
+   * 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.
+   * Range slices on counter column family is not yet supported (https://issues.apache.org/jira/browse/CASSANDRA-2342).
- 
- == Operational considerations ==
-   * Reusing IP addresses will cause problems. Since the current version of the patch uses machine ip addresses in the on disk data format as an identifier a reuse of an old address will result in incorrect counts.
-     * See https://issues.apache.org/jira/browse/CASSANDRA-1944 and https://issues.apache.org/jira/browse/CASSANDRA-1938
  
  == Further reading ==
- See [[https://issues.apache.org/jira/browse/CASSANDRA-1072|CASSANDRA-1072]] and especially the [[https://issues.apache.org/jira/secure/attachment/12459754/Partitionedcountersdesigndoc.pdf|design doc]] for further information about how this works.
+ See [[https://issues.apache.org/jira/browse/CASSANDRA-1072|CASSANDRA-1072]] and especially the [[https://issues.apache.org/jira/secure/attachment/12459754/Partitionedcountersdesigndoc.pdf|design doc]] for further information about how this works internally.