From 073e00c0053cb351dbba265112a6e756c932f875 Mon Sep 17 00:00:00 2001
From: ramkrishna <ramkrishna.s.vasudevan@gmail.com>
Date: Wed, 6 Jan 2016 10:38:27 +0530
Subject: [PATCH] HBASE-14221 Reduce the number of time row comparison is done
 in a Scan (Ram)

---
 .../hbase/regionserver/ScanQueryMatcher.java  | 36 +++++++++++--------
 .../hbase/regionserver/StoreScanner.java      | 11 +++---
 2 files changed, 27 insertions(+), 20 deletions(-)

diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/ScanQueryMatcher.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/ScanQueryMatcher.java
index 47d8c8fa5ba..c220b5cc8d0 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/ScanQueryMatcher.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/ScanQueryMatcher.java
@@ -283,27 +283,33 @@ public class ScanQueryMatcher {
       if (filter != null && filter.filterAllRemaining()) {
       return MatchCode.DONE_SCAN;
     }
-    int ret = this.rowComparator.compareRows(curCell, cell);
-    if (!this.isReversed) {
-      if (ret <= -1) {
-        return MatchCode.DONE;
-      } else if (ret >= 1) {
-        // could optimize this, if necessary?
-        // Could also be called SEEK_TO_CURRENT_ROW, but this
-        // should be rare/never happens.
-        return MatchCode.SEEK_NEXT_ROW;
+    if (curCell != null) {
+      int ret = this.rowComparator.compareRows(curCell, cell);
+      if (!this.isReversed) {
+        if (ret <= -1) {
+          return MatchCode.DONE;
+        } else if (ret >= 1) {
+          // could optimize this, if necessary?
+          // Could also be called SEEK_TO_CURRENT_ROW, but this
+          // should be rare/never happens.
+          return MatchCode.SEEK_NEXT_ROW;
+        }
+      } else {
+        if (ret <= -1) {
+          return MatchCode.SEEK_NEXT_ROW;
+        } else if (ret >= 1) {
+          return MatchCode.DONE;
+        }
       }
     } else {
-      if (ret <= -1) {
-        return MatchCode.SEEK_NEXT_ROW;
-      } else if (ret >= 1) {
-        return MatchCode.DONE;
-      }
+      // Since the curCell is null it means we are already sure that we have moved over to the next row
+      return MatchCode.DONE;
     }
 
     // optimize case.
-    if (this.stickyNextRow)
+    if (this.stickyNextRow) {
       return MatchCode.SEEK_NEXT_ROW;
+    }
 
     if (this.columns.done()) {
       stickyNextRow = true;
diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StoreScanner.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StoreScanner.java
index 5fdfa79a8ce..3049608ce64 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StoreScanner.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StoreScanner.java
@@ -507,8 +507,7 @@ public class StoreScanner extends NonReversedNonLazyKeyValueScanner
     // If no limits exists in the scope LimitScope.Between_Cells then we are sure we are changing
     // rows. Else it is possible we are still traversing the same row so we must perform the row
     // comparison.
-    if (!scannerContext.hasAnyLimit(LimitScope.BETWEEN_CELLS) || matcher.curCell == null
-        || !CellUtil.matchingRow(cell, matcher.curCell)) {
+    if (!scannerContext.hasAnyLimit(LimitScope.BETWEEN_CELLS) || matcher.curCell == null) {
       this.countPerRow = 0;
       matcher.setToNewRow(cell);
     }
@@ -534,7 +533,6 @@ public class StoreScanner extends NonReversedNonLazyKeyValueScanner
       if (prevCell != cell) ++kvsScanned; // Do object compare - we set prevKV from the same heap.
       checkScanOrder(prevCell, cell, comparator);
       prevCell = cell;
-
       ScanQueryMatcher.MatchCode qcode = matcher.match(cell);
       qcode = optimize(qcode, cell);
       switch (qcode) {
@@ -553,6 +551,7 @@ public class StoreScanner extends NonReversedNonLazyKeyValueScanner
           if (!matcher.moreRowsMayExistAfter(cell)) {
             return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
           }
+          matcher.curCell = null;
           seekToNextRow(cell);
           break LOOP;
         }
@@ -580,6 +579,7 @@ public class StoreScanner extends NonReversedNonLazyKeyValueScanner
           if (!matcher.moreRowsMayExistAfter(cell)) {
             return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
           }
+          matcher.curCell = null;
           seekToNextRow(cell);
         } else if (qcode == ScanQueryMatcher.MatchCode.INCLUDE_AND_SEEK_NEXT_COL) {
           seekAsDirection(matcher.getKeyForNextColumn(cell));
@@ -596,6 +596,7 @@ public class StoreScanner extends NonReversedNonLazyKeyValueScanner
         continue;
 
       case DONE:
+        matcher.curCell = null;
         return scannerContext.setScannerState(NextState.MORE_VALUES).hasMoreValues();
 
       case DONE_SCAN:
@@ -608,7 +609,7 @@ public class StoreScanner extends NonReversedNonLazyKeyValueScanner
         if (!matcher.moreRowsMayExistAfter(cell)) {
           return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
         }
-
+        matcher.curCell = null;
         seekToNextRow(cell);
         break;
 
@@ -751,7 +752,7 @@ public class StoreScanner extends NonReversedNonLazyKeyValueScanner
     }
     if ((matcher.curCell == null) || !CellUtil.matchingRows(cell, matcher.curCell)) {
       this.countPerRow = 0;
-      matcher.reset();
+      // The setToNewRow will call reset internally
       matcher.setToNewRow(cell);
     }
   }