WT_SESSION.prepare doesn't permit WT_SESSION.timestamp_transaction,

instead it requires the timestamp be set at transaction commit.

test/format/ops.c

@@ -586,31 +586,41 @@ set_commit_timestamp(TINFO *tinfo)
  *     Commit a transaction.
  */
 static void
-commit_transaction(TINFO *tinfo, WT_SESSION *session)
+commit_transaction(TINFO *tinfo, WT_SESSION *session, bool prepared)
 {
 	uint64_t ts;
-	char config_buf[64];
+	char *config, config_buf[64];
 
+	config = NULL;
 	if (g.c_txn_timestamps) {
 		ts = set_commit_timestamp(tinfo);
 		testutil_check(__wt_snprintf(
 		    config_buf, sizeof(config_buf),
 		    "commit_timestamp=%" PRIx64, ts));
+		config = config_buf;
+	}
+
+	if (prepared)
 		testutil_check(
-		    session->timestamp_transaction(session, config_buf));
+		    session->commit_transaction(session, config));
 
-		/*
-		 * Clear the thread's active timestamp: it no longer needs to
-		 * be pinned.  Don't let the compiler re-order this statement,
-		 * if we were to race with the timestamp thread, it might see
-		 * our thread update before the commit_timestamp is set for the
-		 * transaction.
-		 */
-		if (g.c_txn_timestamps)
-			WT_PUBLISH(tinfo->commit_timestamp, 0);
-	}
+	if (!prepared)
+		testutil_check(
+		    session->timestamp_transaction(session, config));
+
+	/*
+	 * Clear the thread's active timestamp: it no longer needs to
+	 * be pinned.  Don't let the compiler re-order this statement,
+	 * if we were to race with the timestamp thread, it might see
+	 * our thread update before the commit_timestamp is set for the
+	 * transaction.
+	 */
+	if (g.c_txn_timestamps)
+		WT_PUBLISH(tinfo->commit_timestamp, 0);
+
+	if (!prepared)
+		testutil_check(session->commit_transaction(session, NULL));
 
-	testutil_check(session->commit_transaction(session, NULL));
 	++tinfo->commit;
 }
 
@@ -705,7 +715,7 @@ ops(void *arg)
 	uint64_t reset_op, session_op, truncate_op;
 	uint32_t range, rnd;
 	u_int i, j, iso_config;
-	bool greater_than, intxn, next, positioned, readonly;
+	bool greater_than, intxn, next, positioned, prepared, readonly;
 
 	tinfo = arg;
 
@@ -746,7 +756,7 @@ ops(void *arg)
 			 * resolve any running transaction.
 			 */
 			if (intxn) {
-				commit_transaction(tinfo, session);
+				commit_transaction(tinfo, session, false);
 				intxn = false;
 			}
 
@@ -1109,12 +1119,14 @@ ops(void *arg)
 		 * If prepare configured, prepare the transaction 10% of the
 		 * time.
 		 */
+		prepared = false;
 		if (g.c_prepare && mmrand(&tinfo->rnd, 1, 10) == 1) {
 			ret = prepare_transaction(tinfo, session);
 			testutil_assert(ret == 0 || ret == WT_PREPARE_CONFLICT);
 			if (ret == WT_PREPARE_CONFLICT)
 				goto deadlock;
 
+			prepared = true;
 			__wt_yield();		/* Let other threads proceed. */
 		}
 
@@ -1124,7 +1136,7 @@ ops(void *arg)
 		 */
 		switch (rnd) {
 		case 1: case 2: case 3: case 4:			/* 40% */
-			commit_transaction(tinfo, session);
+			commit_transaction(tinfo, session, prepared);
 			break;
 		case 5:						/* 10% */
 			if (0) {