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https://issues.apache.org/jira/browse/CASSANDRA-3638?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13172252#comment-13172252
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MaHaiyang commented on CASSANDRA-3638:
--------------------------------------
{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);
if (pred.apply(ici))
return ici;
}
return endOfData();
{code}
The 'iter' is a submap of memtable's columnFamilies . If pred.apply(ici) ==
false , 'iter' will iterate to the end .
Suppose 'iter' is [ c ,d ,e ,f ] , pred.startKey is a ,and endKey is b ,
pred.apply(ici) will always be false .
In fact ,in this case , 'iter' never need to iterate , and should directly
return endOfData() . This is the problem!
So , can anybody review the code too ?
> 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 .
> {color:red} // this iterator may iterate the whole memtable!!{color}
> {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()) // this iterator may iterate the
> whole memtable!!
> {
> ....
> }
> }
> .....
> }
> .....
> return rows;
> }
> {code}
> {color:red} // Just only query one row ,but returned a sublist of
> columnFamiles {color}
> {code:title=Memtable.java|borderStyle=solid}
> // Just only query one row ,but returned a sublist of columnFamiles
> public Iterator<Map.Entry<DecoratedKey, ColumnFamily>>
> getEntryIterator(DecoratedKey startWith)
> {
> return columnFamilies.tailMap(startWith).entrySet().iterator();
> }
> {code}
> {color:red} // entry.getKey() will never bigger or equal to startKey, and
> then iterate the whole sublist of memtable {color}
> {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);
> // entry.getKey() will never bigger or equal to startKey, and
> then iterate the whole sublist of memtable
> if (pred.apply(ici))
> return ici;
> }
> return endOfData();
> {code}
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