3 files changed, 40 insertions, 25 deletions

diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 04610ccf5e8..b9511df2c26 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -2112,19 +2112,12 @@ PQgetResult(PGconn *conn)
 			break;
 
 		case PGASYNC_READY:
-
-			/*
-			 * For any query type other than simple query protocol, we advance
-			 * the command queue here.  This is because for simple query
-			 * protocol we can get the READY state multiple times before the
-			 * command is actually complete, since the command string can
-			 * contain many queries.  In simple query protocol, the queue
-			 * advance is done by fe-protocol3 when it receives ReadyForQuery.
-			 */
-			if (conn->cmd_queue_head &&
-				conn->cmd_queue_head->queryclass != PGQUERY_SIMPLE)
-				pqCommandQueueAdvance(conn);
 			res = pqPrepareAsyncResult(conn);
+
+			/* Advance the queue as appropriate */
+			pqCommandQueueAdvance(conn, false,
+								  res->resultStatus == PGRES_PIPELINE_SYNC);
+
 			if (conn->pipelineStatus != PQ_PIPELINE_OFF)
 			{
 				/*
@@ -3088,18 +3081,44 @@ PQexitPipelineMode(PGconn *conn)
 
 /*
  * pqCommandQueueAdvance
- *		Remove one query from the command queue, when we receive
- *		all results from the server that pertain to it.
+ *		Remove one query from the command queue, if appropriate.
+ *
+ * If we have received all results corresponding to the head element
+ * in the command queue, remove it.
+ *
+ * In simple query protocol we must not advance the command queue until the
+ * ReadyForQuery message has been received.  This is because in simple mode a
+ * command can have multiple queries, and we must process result for all of
+ * them before moving on to the next command.
+ *
+ * Another consideration is synchronization during error processing in
+ * extended query protocol: we refuse to advance the queue past a SYNC queue
+ * element, unless the result we've received is also a SYNC.  In particular
+ * this protects us from advancing when an error is received at an
+ * inappropriate moment.
  */
 void
-pqCommandQueueAdvance(PGconn *conn)
+pqCommandQueueAdvance(PGconn *conn, bool isReadyForQuery, bool gotSync)
 {
 	PGcmdQueueEntry *prevquery;
 
 	if (conn->cmd_queue_head == NULL)
 		return;
 
-	/* delink from queue */
+	/*
+	 * If processing a query of simple query protocol, we only advance the
+	 * queue when we receive the ReadyForQuery message for it.
+	 */
+	if (conn->cmd_queue_head->queryclass == PGQUERY_SIMPLE && !isReadyForQuery)
+		return;
+
+	/*
+	 * If we're waiting for a SYNC, don't advance the queue until we get one.
+	 */
+	if (conn->cmd_queue_head->queryclass == PGQUERY_SYNC && !gotSync)
+		return;
+
+	/* delink element from queue */
 	prevquery = conn->cmd_queue_head;
 	conn->cmd_queue_head = conn->cmd_queue_head->next;
 
@@ -3107,7 +3126,7 @@ pqCommandQueueAdvance(PGconn *conn)
 	if (conn->cmd_queue_head == NULL)
 		conn->cmd_queue_tail = NULL;
 
-	/* and make it recyclable */
+	/* and make the queue element recyclable */
 	prevquery->next = NULL;
 	pqRecycleCmdQueueEntry(conn, prevquery);
 }
diff --git a/src/interfaces/libpq/fe-protocol3.c b/src/interfaces/libpq/fe-protocol3.c
index 5613c56b141..8c4ec079caa 100644
--- a/src/interfaces/libpq/fe-protocol3.c
+++ b/src/interfaces/libpq/fe-protocol3.c
@@ -240,13 +240,8 @@ pqParseInput3(PGconn *conn)
 					}
 					else
 					{
-						/*
-						 * In simple query protocol, advance the command queue
-						 * (see PQgetResult).
-						 */
-						if (conn->cmd_queue_head &&
-							conn->cmd_queue_head->queryclass == PGQUERY_SIMPLE)
-							pqCommandQueueAdvance(conn);
+						/* Advance the command queue and set us idle */
+						pqCommandQueueAdvance(conn, true, false);
 						conn->asyncStatus = PGASYNC_IDLE;
 					}
 					break;
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 22bc682ffce..7888199b0d9 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -698,7 +698,8 @@ extern void pqSaveMessageField(PGresult *res, char code,
 extern void pqSaveParameterStatus(PGconn *conn, const char *name,
 								  const char *value);
 extern int	pqRowProcessor(PGconn *conn, const char **errmsgp);
-extern void pqCommandQueueAdvance(PGconn *conn);
+extern void pqCommandQueueAdvance(PGconn *conn, bool isReadyForQuery,
+								  bool gotSync);
 extern int	PQsendQueryContinue(PGconn *conn, const char *query);
 
 /* === in fe-protocol3.c === */