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From "MaHaiyang (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-3638) It may iterate the whole memtable while just query one row . This seriously affect the performance . of Cassandra
Date Thu, 15 Dec 2011 13:12:36 GMT
It may iterate the whole memtable while just query one row . This seriously affect the  performance
. of Cassandra
------------------------------------------------------------------------------------------------------------------

                 Key: CASSANDRA-3638
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3638
             Project: Cassandra
          Issue Type: Bug
          Components: Core
    Affects Versions: 1.0.0
            Reporter: MaHaiyang


RangeSliceVerbHandler may  just only query one row , but cassandra may iterate the whole memtable
.
the problem is in ColumnFamilyStore.getRangeSlice() method .
{code:title=ColumnFamilyStore.java|borderStyle=solid}
 public List<Row> getRangeSlice(ByteBuffer superColumn, final AbstractBounds range,
int maxResults, IFilter columnFilter)
    throws ExecutionException, InterruptedException
    {
    ...
        DecoratedKey startWith = new DecoratedKey(range.left, null);
        DecoratedKey stopAt = new DecoratedKey(range.right, null);

        QueryFilter filter = new QueryFilter(null, new QueryPath(columnFamily, superColumn,
null), columnFilter);
        int gcBefore = (int)(System.currentTimeMillis() / 1000) - metadata.getGcGraceSeconds();

        List<Row> rows;
        ViewFragment view = markReferenced(startWith, stopAt);
        try
        {
            CloseableIterator<Row> iterator = RowIteratorFactory.getIterator(view.memtables,
view.sstables, startWith, stopAt, filter, getComparator(), this);
            rows = new ArrayList<Row>();

            try
            {
                // pull rows out of the iterator
                boolean first = true;
                while (iterator.hasNext()) {color:red} 
// this iterator may iterate the whole memtable!!
 
{color}                 
               {
                    ....
                }
            }
          .....
        }
       .....
        return rows;
    }

{code} 

{code:title=Memtable.java|borderStyle=solid}
{color:red} 
// Just only query one row ,but returned a sublist of columnFamiles   
{color}  
public Iterator<Map.Entry<DecoratedKey, ColumnFamily>> getEntryIterator(DecoratedKey
startWith)
    {
        return columnFamilies.tailMap(startWith).entrySet().iterator();
    }
{code} 



{code:title=RowIteratorFactory.java|borderStyle=solid}
 public IColumnIterator computeNext()
        {
            while (iter.hasNext())
            {
                Map.Entry<DecoratedKey, ColumnFamily> entry = iter.next();
                IColumnIterator ici = filter.getMemtableColumnIterator(entry.getValue(), entry.getKey(),
comparator);
{color:red} 
// entry.getKey() will never bigger or equal to startKey, and then iterate the whole sublist
of memtable 
{color}             
                if (pred.apply(ici))  
                    return ici;
            }
            return endOfData();
{code} 







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