Throttle indexing when disk IO throttling is disabled

docs/changelog/129245.yaml

@@ -0,0 +1,5 @@
+pr: 129245
+summary: Throttle indexing when disk IO throttling is disabled
+area: Engine
+type: enhancement
+issues: []

server/src/main/java/org/elasticsearch/index/engine/ThreadPoolMergeScheduler.java

@@ -244,8 +244,8 @@ private void checkMergeTaskThrottling() {
         // both currently running and enqueued merge tasks are considered "active" for throttling purposes
         int activeMerges = (int) (submittedMergesCount - doneMergesCount);
         if (activeMerges > configuredMaxMergeCount
-            // only throttle indexing if disk IO is un-throttled, and we still can't keep up with the merge load
-            && threadPoolMergeExecutorService.usingMaxTargetIORateBytesPerSec()
+            // only throttle indexing if disk IO is un-throttled (if enabled), and we still can't keep up with the merge load
+            && (config.isAutoThrottle() == false || threadPoolMergeExecutorService.usingMaxTargetIORateBytesPerSec())
             && shouldThrottleIncomingMerges.get() == false) {
             // maybe enable merge task throttling
             synchronized (shouldThrottleIncomingMerges) {

server/src/test/java/org/elasticsearch/index/engine/ThreadPoolMergeSchedulerTests.java

@@ -196,7 +196,15 @@ public void testSimpleMergeTaskReEnqueueingBySize() {
         }
     }
 
-    public void testIndexingThrottlingWhenSubmittingMerges() {
+    public void testIndexingThrottlingWhenSubmittingMergesWithDiskIOThrottlingEnabled() {
+        testIndexingThrottlingWhenSubmittingMerges(true);
+    }
+
+    public void testIndexingThrottlingWhenSubmittingMergesWithDiskIOThrottlingDisabled() {
+        testIndexingThrottlingWhenSubmittingMerges(false);
+    }
+
+    private void testIndexingThrottlingWhenSubmittingMerges(boolean withDiskIOThrottlingEnabled) {
         final int maxThreadCount = randomIntBetween(1, 5);
         // settings validation requires maxMergeCount >= maxThreadCount
         final int maxMergeCount = maxThreadCount + randomIntBetween(0, 5);
@@ -209,6 +217,7 @@ public void testIndexingThrottlingWhenSubmittingMerges() {
         Settings mergeSchedulerSettings = Settings.builder()
             .put(MergeSchedulerConfig.MAX_THREAD_COUNT_SETTING.getKey(), maxThreadCount)
             .put(MergeSchedulerConfig.MAX_MERGE_COUNT_SETTING.getKey(), maxMergeCount)
+            .put(MergeSchedulerConfig.AUTO_THROTTLE_SETTING.getKey(), withDiskIOThrottlingEnabled)
             .build();
         TestThreadPoolMergeScheduler threadPoolMergeScheduler = new TestThreadPoolMergeScheduler(
             new ShardId("index", "_na_", 1),
@@ -224,20 +233,20 @@ public void testIndexingThrottlingWhenSubmittingMerges() {
         while (submittedMerges < mergesToSubmit - 1) {
             isUsingMaxTargetIORate.set(randomBoolean());
             if (submittedMergeTasks.isEmpty() == false && randomBoolean()) {
-                // maybe schedule one submitted merge
+                // maybe schedule one of the submitted merges (but still it's not run)
                 MergeTask mergeTask = randomFrom(submittedMergeTasks);
                 submittedMergeTasks.remove(mergeTask);
                 mergeTask.schedule();
             } else {
-                // submit one merge
+                // submit one new merge
                 MergeSource mergeSource = mock(MergeSource.class);
                 OneMerge oneMerge = mock(OneMerge.class);
                 when(oneMerge.getStoreMergeInfo()).thenReturn(getNewMergeInfo(randomLongBetween(1L, 10L)));
                 when(oneMerge.getMergeProgress()).thenReturn(new MergePolicy.OneMergeProgress());
                 when(mergeSource.getNextMerge()).thenReturn(oneMerge, (OneMerge) null);
                 threadPoolMergeScheduler.merge(mergeSource, randomFrom(MergeTrigger.values()));
                 submittedMerges++;
-                if (isUsingMaxTargetIORate.get() && submittedMerges > maxMergeCount) {
+                if ((isUsingMaxTargetIORate.get() || withDiskIOThrottlingEnabled == false) && submittedMerges > maxMergeCount) {
                     expectIndexThrottling = true;
                 } else if (submittedMerges <= maxMergeCount) {
                     expectIndexThrottling = false;
@@ -246,15 +255,20 @@ public void testIndexingThrottlingWhenSubmittingMerges() {
             // assert IO throttle state
             assertThat(threadPoolMergeScheduler.isIndexingThrottlingEnabled(), is(expectIndexThrottling));
         }
-        // submit one last merge when IO throttling is at max value
-        isUsingMaxTargetIORate.set(true);
+        if (withDiskIOThrottlingEnabled) {
+            // submit one last merge when IO throttling is at max value
+            isUsingMaxTargetIORate.set(true);
+        } else {
+            // but if disk IO throttling is not enabled, indexing throttling should still be triggered
+            isUsingMaxTargetIORate.set(randomBoolean());
+        }
         MergeSource mergeSource = mock(MergeSource.class);
         OneMerge oneMerge = mock(OneMerge.class);
         when(oneMerge.getStoreMergeInfo()).thenReturn(getNewMergeInfo(randomLongBetween(1L, 10L)));
         when(oneMerge.getMergeProgress()).thenReturn(new MergePolicy.OneMergeProgress());
         when(mergeSource.getNextMerge()).thenReturn(oneMerge, (OneMerge) null);
         threadPoolMergeScheduler.merge(mergeSource, randomFrom(MergeTrigger.values()));
-        // assert index throttling because IO throttling is at max value
+        // assert indexing throttling state because IO throttling is at max value OR disk IO throttling is disabled
         assertThat(threadPoolMergeScheduler.isIndexingThrottlingEnabled(), is(true));
     }