SOLR-6776: only clear changesSinceCommit on a hard commit so tlog will still be flushed on a softCommit

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1642946 13f79535-47bb-0310-9956-ffa450edef68

solr/CHANGES.txt

@@ -509,6 +509,10 @@ Bug Fixes
 * SOLR-6796: distrib.singlePass does not return correct set of fields for multi-fl-parameter
   requests. (Per Steffensen via shalin)
 
+* SOLR-6776: Transaction log was not flushed at the end of update requests with softCommit
+  specified, which could lead to data loss if the server were killed immediately after the
+  update finished.  (Jeffery Yuan via yonik)
+
 Other Changes
 ----------------------
 

solr/core/src/java/org/apache/solr/update/processor/RunUpdateProcessorFactory.java

@@ -94,7 +94,10 @@ class RunUpdateProcessor extends UpdateRequestProcessor
   {
     updateHandler.commit(cmd);
     super.processCommit(cmd);
-    changesSinceCommit = false;
+    if (!cmd.softCommit) {
+      // a hard commit means we don't need to flush the transaction log
+      changesSinceCommit = false;
+    }
   }
 
   /**