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Subject: svn commit: r1459839 - in /db/derby/code/branches/10.10: ./
java/engine/org/apache/derby/agg/Aggregator.java
Date: Fri, 22 Mar 2013 15:19:12 -0000
To: derby-commits@db.apache.org
From: rhillegas@apache.org
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Author: rhillegas
Date: Fri Mar 22 15:19:12 2013
New Revision: 1459839
URL: http://svn.apache.org/r1459839
Log:
DERBY-672: Port 1459837 from trunk to 10.10 branch.
Modified:
db/derby/code/branches/10.10/ (props changed)
db/derby/code/branches/10.10/java/engine/org/apache/derby/agg/Aggregator.java
Propchange: db/derby/code/branches/10.10/
------------------------------------------------------------------------------
Merged /db/derby/code/trunk:r1459837
Modified: db/derby/code/branches/10.10/java/engine/org/apache/derby/agg/Aggregator.java
URL: http://svn.apache.org/viewvc/db/derby/code/branches/10.10/java/engine/org/apache/derby/agg/Aggregator.java?rev=1459839&r1=1459838&r2=1459839&view=diff
==============================================================================
--- db/derby/code/branches/10.10/java/engine/org/apache/derby/agg/Aggregator.java (original)
+++ db/derby/code/branches/10.10/java/engine/org/apache/derby/agg/Aggregator.java Fri Mar 22 15:19:12 2013
@@ -39,10 +39,22 @@ public interface Aggregator
* For merging another partial result into this Aggregator.
* This lets the SQL interpreter divide the incoming rows into
* subsets, aggregating each subset in isolation, and then merging
- * the partial results together.
+ * the partial results together. This method can be called when
+ * performing a grouped aggregation with a large number of groups.
+ * While processing such a query, Derby may write intermediate grouped
+ * results to disk. The intermediate results may be retrieved and merged
+ * with later results if Derby encounters later rows which belong to groups
+ * whose intermediate results have been written to disk. This situation can
+ * occur with a query like the following:
+ *
+ *
+ *
+ * select a, mode( b ) from mode_inputs group by a order by a
+ *
*/
public void merge( A otherAggregator );