HBASE-8669 change exploring compaction policy to prefer smaller compactions on blocked stores

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1495261 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -97,9 +97,7 @@ public class ExploringCompactionPolicy extends RatioBasedCompactionPolicy {
         }
 
         ++optsInRatio;
-        // Keep if this gets rid of more files.  Or the same number of files for less io.
+        if (isBetterSelection(bestSelection, bestSize, potentialMatchFiles, size, mightBeStuck)) {
-        if (potentialMatchFiles.size() > bestSelection.size()
-            || (potentialMatchFiles.size() == bestSelection.size() && size < bestSize)) {
           bestSelection = potentialMatchFiles;
           bestSize = size;
           bestStart = start;
@@ -117,6 +115,22 @@ public class ExploringCompactionPolicy extends RatioBasedCompactionPolicy {
     return new ArrayList<StoreFile>(bestSelection);
   }
 
+  private boolean isBetterSelection(List<StoreFile> bestSelection,
+      long bestSize, List<StoreFile> selection, long size, boolean mightBeStuck) {
+    if (mightBeStuck && bestSize > 0 && size > 0) {
+      // Keep the selection that removes most files for least size. That penaltizes adding
+      // large files to compaction, but not small files, so we don't become totally inefficient
+      // (might want to tweak that in future). Also, given the current order of looking at
+      // permutations, prefer earlier files and smaller selection if the difference is small.
+      final double REPLACE_IF_BETTER_BY = 1.05;
+      double thresholdQuality = ((double)bestSelection.size() / bestSize) * REPLACE_IF_BETTER_BY;
+      return thresholdQuality < ((double)selection.size() / size);
+    }
+    // Keep if this gets rid of more files.  Or the same number of files for less io.
+    return selection.size() > bestSelection.size()
+      || (selection.size() == bestSelection.size() && size < bestSize);
+  }
+
   /**
    * Find the total size of a list of store files.
    * @param potentialMatchFiles StoreFile list.

hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestDefaultCompactSelection.java

@@ -345,4 +345,18 @@ public class TestDefaultCompactSelection extends TestCase {
     compactEquals(sfCreate(999, 50, 12, 12, 1), false, true, 50, 12, 12, 1);
     compactEquals(sfCreate(999, 50, 12, 12, 1), 12, 12, 1);
   }
+
+  public void testStuckStoreCompaction() throws IOException {
+    // Select the smallest compaction if the store is stuck.
+    compactEquals(sfCreate(99,99,99,99,99,99, 30,30,30,30), 30, 30, 30);
+    // If not stuck, standard policy applies.
+    compactEquals(sfCreate(99,99,99,99,99, 30,30,30,30), 99, 30, 30, 30, 30);
+
+    // Add sufficiently small files to compaction, though
+    compactEquals(sfCreate(99,99,99,99,99,99, 30,30,30,15), 30, 30, 30, 15);
+    // Prefer earlier compaction to latter if the benefit is not significant
+    compactEquals(sfCreate(99,99,99,99, 30,26,26,29,25,25), 30, 26, 26);
+    // Prefer later compaction if the benefit is significant.
+    compactEquals(sfCreate(99,99,99,99, 27,27,27,20,20,20), 20, 20, 20);
+  }
 }