keith-turner opened a new issue #946: Create a column buffer class for 
GarbageCollectionIterator
URL: https://github.com/apache/fluo/issues/946
 
 
   Fluo has a [GarbageCollectionIterator][1] that cleans up bookkeeping info 
created by transactions that is no longer needed.  For this iterator to do its 
job, it must [buffer][2] a row/column in memory.  For this particular case, the 
row column in each buffered key is always the same.  Therefore it would be more 
memory efficient to just buffer the timestamp and value.  The could be done by 
creating a new class like the following and modifying GarbageCollectionIterator 
to use it.
   
   ```java
   /**
    * This class buffers Keys that all have the same row+column.  Internally it 
only stores one Key, a list of timestamps and a list of values.  At iteration 
time it materializes each Key+Value.
    */
   class ColumnBuffer Iterable<KeyValue> {
     /**
      * When empty, the first key added sets the row+column.  After this all 
keys added must have the same
      * row+column.
      */
     public void add(Key k, Value v);
     Iterator<KeyValue> iterator();
     clear();
   }
   ```
   
   [1]: 
https://github.com/apache/fluo/blob/rel/fluo-1.1.0-incubating/modules/accumulo/src/main/java/org/apache/fluo/accumulo/iterators/GarbageCollectionIterator.java
   [2]: 
https://github.com/apache/fluo/blob/rel/fluo-1.1.0-incubating/modules/accumulo/src/main/java/org/apache/fluo/accumulo/iterators/GarbageCollectionIterator.java#L68

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