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https://issues.apache.org/jira/browse/TRAFODION-2259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15546971#comment-15546971
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ASF GitHub Bot commented on TRAFODION-2259:
-------------------------------------------
Github user DaveBirdsall commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/743#discussion_r81871556
--- Diff: core/sql/sort/Topn.cpp ---
@@ -0,0 +1,337 @@
+/**********************************************************************
+// @@@ START COPYRIGHT @@@
+//
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+//
+// @@@ END COPYRIGHT @@@
+**********************************************************************/
+/* -*-C++-*-
+******************************************************************************
+*
+* File: TopN.cpp
+*
+* Description: This file contains the implementation of all member
functions
+* of the class TopN.
+*
+* 1. Sort would initially maintain Top N array of elements to being with.
+* 2. Read records into TopN array.
+* 3. Once TopN array is full, heapify the array into max heap. Top node in
the heap is always the highest node.
+* 4. Subsequent record read either gets discarded( if greater than top
node) or replace top node( if lesser then top node) . if replaced top node,
re-balance the heap.
+* 5. Repeat steps 4 until last record is read.
+* 6. sort the final heap using heap sort.
+*******************************************************************************/
+
+#include <iostream>
+#include <fstream>
+
+#ifndef DEBUG
+#undef NDEBUG
+#define NDEBUG
+#endif
+#include "ex_stdh.h"
+#include "Topn.h"
+#include "ScratchSpace.h"
+#include "logmxevent.h"
+#include "SortUtil.h"
+#include "ex_ex.h"
+#include "ExStats.h"
+
+//------------------------------------------------------------------------
+// Class Constructor.
+//------------------------------------------------------------------------
+TopN::TopN(ULng32 runsize, ULng32 sortmaxmem, ULng32 recsize,
+ NABoolean doNotallocRec, ULng32 keysize,
+ SortScratchSpace* scratch, NABoolean iterSort,
+ CollHeap* heap, SortError* sorterror, Lng32 explainNodeId,
SortUtil* sortutil):
+ SortAlgo(runsize, recsize, doNotallocRec, keysize, scratch,
explainNodeId),
+ loopIndex_(0), heap_(heap), sortError_(sorterror),
+ sortUtil_(sortutil)
+{
+ //runsize is TopN size. Fixed.
+ allocRunSize_ = runsize;
+
+ //Actual run size after all elements read.
+ runSize_ = 0;
+
+ isHeapified_ = FALSE;
+
+ //allocateMemory failureIsFatal is defaulted to TRUE means allocation
failure results in
+ //longjump to jump handler defined in ex_sort.cpp. Only applicable on
NSK.
--- End diff --
Is there a reason to perpetuate NSK-isms?
> Sort TopN operator
> ------------------
>
> Key: TRAFODION-2259
> URL: https://issues.apache.org/jira/browse/TRAFODION-2259
> Project: Apache Trafodion
> Issue Type: Improvement
> Components: sql-exe
> Affects Versions: 2.1-incubating
> Reporter: Prashanth Vasudev
> Assignee: Prashanth Vasudev
>
> Sort operator consumes all records before producing sorted records. For
> certain use cases where only Top N records are required, today sort consumes
> all records into memory and overflows( spills ) to disk. This impacts
> performance.
> if topN is pushed down to sort, only required memory can be allocated and
> sort would only hold topN records in memory. Once all the records are read,
> sorted records in topN is returned.
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