`_flush` should block by default (#20597)

This commit changes the default behavior of `_flush` to block if other flushes are ongoing.
This also removes the use of `FlushNotAllowedException` and instead simply return immediately
by skipping the flush. Users should be aware if they set this option that the flush might or might
not flush everything to disk ie. no transactional behavior of some sort.

Closes #20569

1 files changed, 1 insertions, 6 deletions

diff --git a/core/src/test/java/org/elasticsearch/versioning/SimpleVersioningIT.java b/core/src/test/java/org/elasticsearch/versioning/SimpleVersioningIT.java
index b80c5bd8e2..c5d0129644 100644
--- a/core/src/test/java/org/elasticsearch/versioning/SimpleVersioningIT.java
+++ b/core/src/test/java/org/elasticsearch/versioning/SimpleVersioningIT.java
@@ -29,7 +29,6 @@ import org.elasticsearch.action.search.SearchResponse;
 import org.elasticsearch.common.lucene.uid.Versions;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.index.VersionType;
-import org.elasticsearch.index.engine.FlushNotAllowedEngineException;
 import org.elasticsearch.index.engine.VersionConflictEngineException;
 import org.elasticsearch.test.ESIntegTestCase;
 
@@ -617,11 +616,7 @@ public class SimpleVersioningIT extends ESIntegTestCase {
                             }
                             if (threadRandom.nextInt(100) == 7) {
                                 logger.trace("--> {}: TEST: now flush at {}", threadID, System.nanoTime() - startTime);
-                                try {
-                                    flush();
-                                } catch (FlushNotAllowedEngineException fnaee) {
-                                    // OK
-                                }
+                                flush();
                                 logger.trace("--> {}: TEST: flush done at {}", threadID, System.nanoTime() - startTime);
                             }
                         }