Add comments

Author: ankikuma

server/src/main/java/org/elasticsearch/index/shard/IndexShard.java

@@ -3245,7 +3245,7 @@ public void noopUpdate() {
      * @see org.elasticsearch.indices.IndexingMemoryController
      */
     public void writeIndexBuffersOnIndexThreads(long took) {
-        internalIndexingStats.writeIndexBuffers(took);
+        internalIndexingStats.writeIndexingBuffersTime(took);
     }
 
     public void maybeCheckIndex() {

server/src/main/java/org/elasticsearch/index/shard/InternalIndexingStats.java

@@ -166,22 +166,26 @@ void noopUpdate() {
      * @param took   time taken to write buffers
      * @see org.elasticsearch.indices.IndexingMemoryController
      */
-    void writeIndexBuffers(long took) {
+    void writeIndexingBuffersTime(long took) {
         totalStats.writeIndexingBufferTime.add(took);
         totalStats.recentIndexMetric.addIncrement(took, relativeTimeInNanosSupplier.getAsLong());
     }
 
     static class StatsHolder {
         private final MeanMetric indexMetric = new MeanMetric(); // Used for the count and total 'took' time (in ns) of index operations
-        private final ExponentiallyWeightedMovingRate recentIndexMetric; // An EWMR of the total 'took' time of index operations (in ns)
-        private final AtomicReference<Double> peakIndexMetric; // The peak value of the EWMR observed in any stats() call
+        private final LongAdder writeIndexingBufferTime = new LongAdder();
+        // Used for the total time taken to flush indexing buffers to disk (on indexing threads) (in ns)
+        private final ExponentiallyWeightedMovingRate recentIndexMetric;
+        // An EWMR of the total 'took' time of index operations (in ns) plus the writeIndexingBufferTime
+        private final AtomicReference<Double> peakIndexMetric;
+        // The peak value of the EWMR (recentIndexMetric) observed in any stats() call
         private final MeanMetric deleteMetric = new MeanMetric();
         private final CounterMetric indexCurrent = new CounterMetric();
         private final CounterMetric indexFailed = new CounterMetric();
         private final CounterMetric indexFailedDueToVersionConflicts = new CounterMetric();
         private final CounterMetric deleteCurrent = new CounterMetric();
         private final CounterMetric noopUpdates = new CounterMetric();
-        private final LongAdder writeIndexingBufferTime = new LongAdder();
+
 
         StatsHolder(long startTimeInNanos, TimeValue recentWriteLoadHalfLife) {
             double lambdaInInverseNanos = Math.log(2.0) / recentWriteLoadHalfLife.nanos();

server/src/main/java/org/elasticsearch/indices/IndexingMemoryController.java

@@ -211,6 +211,7 @@ private boolean writePendingIndexingBuffers() {
             .pollFirst()) {
             // Remove the shard from the set first, so that multiple threads can run writeIndexingBuffer concurrently on the same shard.
             pendingWriteIndexingBufferSet.remove(shard);
+            // Calculate the time taken to write the indexing buffers so it can be accounted for in the index write load
             startTime = System.nanoTime();
             shard.writeIndexingBuffer();
             took = System.nanoTime() - startTime;

server/src/test/java/org/elasticsearch/index/shard/IndexingStatsTests.java

@@ -33,7 +33,7 @@ public void testStatsGetWriteLoad() {
             false,
             10,
             1_800_000_000L, // totalIndexingTimeSinceShardStartedInNanos - 1.8sec
-            1_800_000_000L, // totalIndexingTimeSinceShardStartedInNanos - 1.8sec
+            1_800_000_000L, // totalIndexingLoadSinceShardStartedInNanos - 1.8sec
             3_000_000_000L, // totalActiveTimeInNanos - 3sec
             0.1357,
             0.2468
@@ -106,7 +106,7 @@ public void testStatsAdd_writeLoads() {
             false,
             10,
             1_000_000_000L, // totalIndexingTimeSinceShardStartedInNanos - 1sec
-            1_000_000_000L, // totalIndexingTimeSinceShardStartedInNanos - 1sec
+            1_000_000_000L, // totalIndexingLoadSinceShardStartedInNanos - 1sec
             2_000_000_000L, // totalActiveTimeInNanos - 2sec
             0.1357, // recentWriteLoad
             0.3579 // peakWriteLoad