Add debug log for flush for IndicesRequestCacheIT (#39475)

Add debug log when index is flushed to investigate a failure
in IndicesRequestCacheIT

"DEBUG" level is used as "TRACE" produces too  much output irrelevant for this
issue

Relates to #32827

Author: mayya-sharipova

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

@@ -1715,13 +1715,20 @@ public CommitId flush(boolean force, boolean waitIfOngoing) throws EngineExcepti
             try {
                 // Only flush if (1) Lucene has uncommitted docs, or (2) forced by caller, or (3) the
                 // newly created commit points to a different translog generation (can free translog)
-                if (indexWriter.hasUncommittedChanges() || force || shouldPeriodicallyFlush()) {
+                boolean hasUncommittedChanges = indexWriter.hasUncommittedChanges();
+                boolean shouldPeriodicallyFlush = shouldPeriodicallyFlush();
+                if (hasUncommittedChanges || force || shouldPeriodicallyFlush) {
                     ensureCanFlush();
                     try {
                         translog.rollGeneration();
                         logger.trace("starting commit for flush; commitTranslog=true");
                         commitIndexWriter(indexWriter, translog, null);
                         logger.trace("finished commit for flush");
+
+                        // a temporary debugging to investigate test failure - issue#32827. Remove when the issue is resolved
+                        logger.debug("new commit on flush, hasUncommittedChanges:{}, force:{}, shouldPeriodicallyFlush:{}",
+                            hasUncommittedChanges, force, shouldPeriodicallyFlush);
+
                         // we need to refresh in order to clear older version values
                         refresh("version_table_flush", SearcherScope.INTERNAL, true);
                         translog.trimUnreferencedReaders();

server/src/test/java/org/elasticsearch/indices/IndicesRequestCacheIT.java

@@ -51,7 +51,7 @@
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.greaterThan;
 
-@TestLogging(value = "org.elasticsearch.indices.IndicesRequestCache:TRACE")
+@TestLogging(value = "org.elasticsearch.indices.IndicesRequestCache:TRACE,org.elasticsearch.index.engine.Engine:DEBUG")
 public class IndicesRequestCacheIT extends ESIntegTestCase {
 
     // One of the primary purposes of the query cache is to cache aggs results