From a51dc02ed3b7252add956dd81f712c7f7053d823 Mon Sep 17 00:00:00 2001
From: Elliott Clark <eclark@apache.org>
Date: Fri, 18 Dec 2015 14:14:25 -0800
Subject: [PATCH] HBASE-15014 Fix filterCellByStore in WALsplitter is awful for
 performance

---
 .../hbase/regionserver/wal/WALEdit.java       | 14 ++++++++++++-
 .../apache/hadoop/hbase/wal/WALSplitter.java  | 20 ++++++++++++-------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/WALEdit.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/WALEdit.java
index 5e53e411243..c47ce13b307 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/WALEdit.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/WALEdit.java
@@ -99,7 +99,7 @@ public class WALEdit implements Writable, HeapSize {
   private final int VERSION_2 = -1;
   private final boolean isReplay;
 
-  private final ArrayList<Cell> cells = new ArrayList<Cell>(1);
+  private ArrayList<Cell> cells = new ArrayList<Cell>(1);
 
   public static final WALEdit EMPTY_WALEDIT = new WALEdit();
 
@@ -170,6 +170,18 @@ public class WALEdit implements Writable, HeapSize {
     return cells;
   }
 
+  /**
+   * This is not thread safe.
+   * This will change the WALEdit and shouldn't be used unless you are sure that nothing
+   * else depends on the contents being immutable.
+   *
+   * @param cells the list of cells that this WALEdit now contains.
+   */
+  @InterfaceAudience.Private
+  public void setCells(ArrayList<Cell> cells) {
+    this.cells = cells;
+  }
+
   public NavigableMap<byte[], Integer> getAndRemoveScopes() {
     NavigableMap<byte[], Integer> result = scopes;
     scopes = null;
diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/wal/WALSplitter.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/wal/WALSplitter.java
index 98882ff1051..c047f8d6600 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/wal/WALSplitter.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/wal/WALSplitter.java
@@ -1513,21 +1513,27 @@ public class WALSplitter {
       if (maxSeqIdInStores == null || maxSeqIdInStores.isEmpty()) {
         return;
       }
-      List<Cell> skippedCells = new ArrayList<Cell>();
+      // Create the array list for the cells that aren't filtered.
+      // We make the assumption that most cells will be kept.
+      ArrayList<Cell> keptCells = new ArrayList<Cell>(logEntry.getEdit().getCells().size());
       for (Cell cell : logEntry.getEdit().getCells()) {
-        if (!CellUtil.matchingFamily(cell, WALEdit.METAFAMILY)) {
+        if (CellUtil.matchingFamily(cell, WALEdit.METAFAMILY)) {
+          keptCells.add(cell);
+        } else {
           byte[] family = CellUtil.cloneFamily(cell);
           Long maxSeqId = maxSeqIdInStores.get(family);
           // Do not skip cell even if maxSeqId is null. Maybe we are in a rolling upgrade,
           // or the master was crashed before and we can not get the information.
-          if (maxSeqId != null && maxSeqId.longValue() >= logEntry.getKey().getLogSeqNum()) {
-            skippedCells.add(cell);
+          if (maxSeqId == null || maxSeqId.longValue() < logEntry.getKey().getLogSeqNum()) {
+            keptCells.add(cell);
           }
         }
       }
-      if (!skippedCells.isEmpty()) {
-        logEntry.getEdit().getCells().removeAll(skippedCells);
-      }
+
+      // Anything in the keptCells array list is still live.
+      // So rather than removing the cells from the array list
+      // which would be an O(n^2) operation, we just replace the list
+      logEntry.getEdit().setCells(keptCells);
     }
 
     @Override