HBASE-14227 Reduce the number of time row comparison is done in a Scan

(Ram)

Author: ramkrish86

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/ScanQueryMatcher.java

@@ -278,23 +278,27 @@ public MatchCode match(Cell cell) throws IOException {
     if (filter != null && filter.filterAllRemaining()) {
       return MatchCode.DONE_SCAN;
     }
-    int ret = this.rowComparator.compareRows(row, this.rowOffset, this.rowLength,
+    if (row != null) {
+      int ret = this.rowComparator.compareRows(row, this.rowOffset, this.rowLength,
         cell.getRowArray(), cell.getRowOffset(), cell.getRowLength());
-    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 (!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;
-      }
+      return MatchCode.DONE;
     }
 
     // optimize case.

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StoreScanner.java

@@ -511,8 +511,7 @@ public boolean next(List<Cell> outResult, ScannerContext scannerContext) throws
     // 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.row == null ||
-        !Bytes.equals(row, offset, length, matcher.row, matcher.rowOffset, matcher.rowLength)) {
+    if (!scannerContext.hasAnyLimit(LimitScope.BETWEEN_CELLS) || matcher.row == null) {
       this.countPerRow = 0;
       matcher.setRow(row, offset, length);
     }
@@ -560,6 +559,10 @@ public boolean next(List<Cell> outResult, ScannerContext scannerContext) throws
             if (!matcher.moreRowsMayExistAfter(cell)) {
               return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
             }
+            // Setting the matcher.row = null, will mean that after the subsequent seekToNextRow()
+            // the heap.peek() will any way be in the next row. So the SQM.match(cell) need do
+            // another compareRow to say the current row is DONE
+            matcher.row = null;
             seekToNextRow(cell);
             break LOOP;
           }
@@ -587,6 +590,10 @@ public boolean next(List<Cell> outResult, ScannerContext scannerContext) throws
             if (!matcher.moreRowsMayExistAfter(cell)) {
               return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
             }
+            // Setting the matcher.row = null, will mean that after the subsequent seekToNextRow()
+            // the heap.peek() will any way be in the next row. So the SQM.match(cell) need do
+            // another compareRow to say the current row is DONE
+            matcher.row = null;
             seekToNextRow(cell);
           } else if (qcode == ScanQueryMatcher.MatchCode.INCLUDE_AND_SEEK_NEXT_COL) {
             seekAsDirection(matcher.getKeyForNextColumn(cell));
@@ -603,6 +610,10 @@ public boolean next(List<Cell> outResult, ScannerContext scannerContext) throws
           continue;
 
         case DONE:
+          // We are sure that this row is done and we are in the next row.
+          // So subsequent StoresScanner.next() call need not do another compare
+          // and set the matcher.row
+          matcher.row = null;
           return scannerContext.setScannerState(NextState.MORE_VALUES).hasMoreValues();
 
         case DONE_SCAN:
@@ -615,7 +626,10 @@ public boolean next(List<Cell> outResult, ScannerContext scannerContext) throws
           if (!matcher.moreRowsMayExistAfter(cell)) {
             return scannerContext.setScannerState(NextState.NO_MORE_VALUES).hasMoreValues();
           }
-
+          // Setting the matcher.row = null, will mean that after the subsequent seekToNextRow()
+          // the heap.peek() will any way be in the next row. So the SQM.match(cell) need do
+          // another compareRow to say the current row is DONE
+          matcher.row = null;
           seekToNextRow(cell);
           break;