[HBASE-20628] SegmentScanner does over-comparing when one flushing

• Type: Sub-task
• Status: Resolved
• Priority: Critical
• Resolution: Fixed
• Fix Version/s: 3.0.0, 2.1.0, 2.0.1
• Component/s: Performance
• Hadoop Flags: Reviewed
• Assignee: stack
• Reporter: stack
• Created: 23/May/18 17:17
• Updated: 07/Jun/18 16:08
• Resolved: 04/Jun/18 16:51

Description

Flushing memstore is taking too long. It looks like we are doing a bunch of comparing out of a new facility in hbase2, the Segment scanner at flush time.

Below is a patch from Anoop Sam John. I had a similar more hacky version. Both undo the extra comparing we were seeing in perf tests.

Anastasia Braginsky and Eshcar Hillel. Need your help please.

As I read it, we are trying to flush the memstore snapshot (default, no IMC case). There is only ever going to be one Segment involved (even if IMC is enabled); the snapshot Segment. But the getScanners is returning a list (of one) Scanners and the scan is via the generic SegmentScanner which is all about a bunch of stuff we don't need when doing a flush so it seems to do more work than is necessary. It also supports scanning backwards which is not needed when trying to flush memstore.

Do you see a problem doing a version of Anoops patch (whether IMC or not)? It makes a big difference in general throughput when the below patch is in place. Thanks.

diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreSnapshot.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreSnapshot.java
index cbd60e5da3..c3dd972254 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreSnapshot.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreSnapshot.java
@@ -40,7 +40,8 @@ public class MemStoreSnapshot implements Closeable {
     this.cellsCount = snapshot.getCellsCount();
     this.memStoreSize = snapshot.getMemStoreSize();
     this.timeRangeTracker = snapshot.getTimeRangeTracker();
-    this.scanners = snapshot.getScanners(Long.MAX_VALUE, Long.MAX_VALUE);
+    //this.scanners = snapshot.getScanners(Long.MAX_VALUE, Long.MAX_VALUE);
+    this.scanners = snapshot.getScannersForSnapshot();
     this.tagsPresent = snapshot.isTagsPresent();
   }

diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/Segment.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/Segment.java
index 70074bf3b4..279c4e50c8 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/Segment.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/Segment.java
@@ -33,6 +33,7 @@ import org.apache.hadoop.hbase.KeyValueUtil;
 import org.apache.hadoop.hbase.io.TimeRange;
 import org.apache.hadoop.hbase.util.Bytes;
 import org.apache.hadoop.hbase.util.ClassSize;
+import org.apache.hadoop.hbase.util.CollectionBackedScanner;
 import org.apache.yetus.audience.InterfaceAudience;
 import org.slf4j.Logger;
 import org.apache.hbase.thirdparty.com.google.common.annotations.VisibleForTesting;
@@ -130,6 +131,10 @@ public abstract class Segment {
     return Collections.singletonList(new SegmentScanner(this, readPoint, order));
   }

+  public List<KeyValueScanner> getScannersForSnapshot() {
+    return Collections.singletonList(new CollectionBackedScanner(this.cellSet.get(), comparator));
+  }
+
   /**
    * @return whether the segment has any cells
    */

Issue Links

• is related to: HBASE-20483 [PERFORMANCE] Flushing is 2x slower in hbase2.
• links to: Review Board (branch-2.0)