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Author: jasontedor

core/src/main/java/org/elasticsearch/index/engine/InternalEngine.java

@@ -1917,6 +1917,11 @@ public void onFailure(Exception e) {
 
                 @Override
                 protected void doRun() throws Exception {
+                    /*
+                     * We do this on another thread rather than the merge thread that we are called on so that we have complete confidence
+                     * that the call stack does not contain catch statements that would prevent the error that might be thrown here from
+                     * being caught and never reaching the uncaught exception handler.
+                     */
                     maybeDie("fatal error while merging", exc);
                     logger.error("failed to merge", exc);
                     failEngine("merge failed", new MergePolicy.MergeException(exc, dir));