Warn when an extra-large partition is compacted, CASSANDRA-9643

CHANGES.txt

@@ -13,6 +13,7 @@
  * Add support for selectively varint encoding fields (CASSANDRA-9499)
 
 2.2.0-rc2
+ * Warn when an extra-large partition is compacted (CASSANDRA-9643)
  * (cqlsh) Allow setting the initial connection timeout (CASSANDRA-9601)
  * BulkLoader has --transport-factory option but does not use it (CASSANDRA-9675)
  * Allow JMX over SSL directly from nodetool (CASSANDRA-9090)

conf/cassandra.yaml

@@ -643,6 +643,9 @@ batch_size_fail_threshold_in_kb: 50
 # of compaction, including validation compaction.
 compaction_throughput_mb_per_sec: 16
 
+# Log a warning when compacting partitions larger than this value
+compaction_large_partition_warning_threshold_mb: 100
+
 # When compacting, the replacement sstable(s) can be opened before they
 # are completely written, and used in place of the prior sstables for
 # any range that has been written. This helps to smoothly transfer reads 

src/java/org/apache/cassandra/config/Config.java

@@ -147,6 +147,7 @@ public class Config
     public volatile int batch_size_fail_threshold_in_kb = 50;
     public Integer concurrent_compactors;
     public volatile Integer compaction_throughput_mb_per_sec = 16;
+    public volatile Integer compaction_large_partition_warning_threshold_mb = 100;
 
     public Integer max_streaming_retries = 3;
 

src/java/org/apache/cassandra/config/DatabaseDescriptor.java

@@ -1059,6 +1059,8 @@ public class DatabaseDescriptor
         conf.compaction_throughput_mb_per_sec = value;
     }
 
+    public static int getCompactionLargePartitionWarningThreshold() { return conf.compaction_large_partition_warning_threshold_mb * 1024 * 1024; }
+
     public static boolean getDisableSTCSInL0()
     {
         return Boolean.getBoolean("cassandra.disable_stcs_in_l0");

src/java/org/apache/cassandra/io/sstable/format/big/BigTableWriter.java

@@ -151,7 +151,9 @@ public class BigTableWriter extends SSTableWriter
             RowIndexEntry entry = RowIndexEntry.create(startPosition, iterator.partitionLevelDeletion(), index);
 
             long endPosition = dataFile.getFilePointer();
-            metadataCollector.addPartitionSizeInBytes(endPosition - startPosition);
+            long rowSize = endPosition - startPosition;
+            maybeLogLargePartitionWarning(key, rowSize);
+            metadataCollector.addPartitionSizeInBytes(rowSize);
             afterAppend(key, endPosition, entry);
             return entry;
         }
@@ -161,6 +163,15 @@ public class BigTableWriter extends SSTableWriter
         }
     }
 
+    private void maybeLogLargePartitionWarning(DecoratedKey key, long rowSize)
+    {
+        if (rowSize > DatabaseDescriptor.getCompactionLargePartitionWarningThreshold())
+        {
+            String keyString = metadata.getKeyValidator().getString(key.getKey());
+            logger.warn("Compacting large partition {}/{}:{} ({} bytes)", metadata.ksName, metadata.cfName, keyString, rowSize);
+        }
+    }
+
     private static class StatsCollector extends WrappingUnfilteredRowIterator
     {
         private int cellCount;