Fix threadpool size for SnapshotResiliencyTests

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

@@ -21,6 +21,7 @@
 import org.apache.lucene.store.RateLimitedIndexOutput;
 import org.apache.lucene.store.RateLimiter;
 import org.apache.lucene.util.SetOnce;
+import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.common.logging.Loggers;
 import org.elasticsearch.common.util.concurrent.AbstractRunnable;
 import org.elasticsearch.core.TimeValue;
@@ -35,6 +36,7 @@
 import java.util.HashSet;
 import java.util.Locale;
 import java.util.Set;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 
@@ -64,15 +66,17 @@ public class ThreadPoolMergeScheduler extends MergeScheduler implements Elastics
     private final MergeSchedulerConfig config;
     private final Logger logger;
     private final MergeTracking mergeTracking;
-    private final ThreadPoolExecutor threadPoolExecutor;
+    private final ExecutorService executorService;
+    private final int maxThreadPoolSize;
     private final ThreadLocal<MergeRateLimiter> onGoingMergeRateLimiter = new ThreadLocal<>();
 
     public ThreadPoolMergeScheduler(ShardId shardId, IndexSettings indexSettings, ThreadPool threadPool) {
         this.config = indexSettings.getMergeSchedulerConfig();
         this.logger = Loggers.getLogger(getClass(), shardId);
         this.mergeTracking = new MergeTracking(logger, () -> this.config.isAutoThrottle() ? targetMBPerSec : Double.POSITIVE_INFINITY);
-        // all merge schedulers must use the same thread pool
-        this.threadPoolExecutor = (ThreadPoolExecutor) threadPool.executor(ThreadPool.Names.MERGE);
+        // all merge schedulers must use the same executor of the same thread pool
+        this.executorService = threadPool.executor(ThreadPool.Names.MERGE);
+        this.maxThreadPoolSize = threadPool.info(ThreadPool.Names.MERGE).getMax();
     }
 
     @Override
@@ -131,9 +135,9 @@ protected void handleMergeException(Throwable t) {
     private void submitNewMergeTask(MergeSource mergeSource, MergePolicy.OneMerge merge, MergeTrigger mergeTrigger) {
         MergeTask mergeTask = newMergeTask(mergeSource, merge, mergeTrigger);
         if (mergeTask.isAutoThrottle) {
-            trackNewActiveThrottledMergeTask(mergeTask, threadPoolExecutor.getMaximumPoolSize());
+            trackNewActiveThrottledMergeTask(mergeTask, maxThreadPoolSize);
         }
-        threadPoolExecutor.execute(mergeTask);
+        executorService.execute(mergeTask);
     }
 
     private static double maybeUpdateTargetMBPerSec(int poolSize) {