Create ExecuteOptionalRemoteCommand

A small refactor which pulls some code out of `RecoverWorkerTransactions`
and into `remote_commands.c`. This code block currently only occurs in
`RecoverWorkerTransactions` but will be useful to other functions
shortly.

Unfortunately we couldn't call it `ExecuteRemoteCommand`, that name was
already taken.

src/backend/distributed/connection/remote_commands.c

@@ -229,6 +229,42 @@ ExecuteCriticalRemoteCommand(MultiConnection *connection, const char *command)
 }
 
 
+/*
+ * ExecuteOptionalRemoteCommand executes a remote command. If the command fails a WARNING
+ * is emitted but execution continues.
+ *
+ * could return 0, QUERY_SEND_FAILED, or RESPONSE_NOT_OKAY
+ * result is only set if there was no error
+ */
+int
+ExecuteOptionalRemoteCommand(MultiConnection *connection, const char *command,
+							 PGresult **result)
+{
+	int querySent = 0;
+	PGresult *localResult = NULL;
+	bool raiseInterrupts = true;
+
+	querySent = SendRemoteCommand(connection, command);
+	if (querySent == 0)
+	{
+		ReportConnectionError(connection, WARNING);
+		return QUERY_SEND_FAILED;
+	}
+
+	localResult = GetRemoteCommandResult(connection, raiseInterrupts);
+	if (!IsResponseOK(localResult))
+	{
+		ReportResultError(connection, localResult, WARNING);
+		PQclear(localResult);
+		ForgetResults(connection);
+		return RESPONSE_NOT_OKAY;
+	}
+
+	*result = localResult;
+	return 0;
+}
+
+
 /*
  * SendRemoteCommand is a PQsendQuery wrapper that logs remote commands, and
  * accepts a MultiConnection instead of a plain PGconn.  It makes sure it can

src/backend/distributed/transaction/transaction_recovery.c

@@ -210,9 +210,8 @@ RecoverWorkerTransactions(WorkerNode *workerNode)
 	{
 		char *transactionName = (char *) lfirst(pendingTransactionCell);
 		StringInfo command = makeStringInfo();
-		int querySent = 0;
+		int executeCommand = 0;
 		PGresult *result = NULL;
-		bool raiseInterrupts = true;
 
 		bool shouldCommit = FindMatchingName(unconfirmedTransactionArray,
 											 unconfirmedTransactionCount,
@@ -230,20 +229,13 @@ RecoverWorkerTransactions(WorkerNode *workerNode)
 			appendStringInfo(command, "ROLLBACK PREPARED '%s'", transactionName);
 		}
 
-		querySent = SendRemoteCommand(connection, command->data);
-		if (querySent == 0)
+		executeCommand = ExecuteOptionalRemoteCommand(connection, command->data, &result);
+		if (executeCommand == QUERY_SEND_FAILED)
 		{
-			ReportConnectionError(connection, WARNING);
-
 			break;
 		}
-
-		result = GetRemoteCommandResult(connection, raiseInterrupts);
-		if (!IsResponseOK(result))
+		if (executeCommand == RESPONSE_NOT_OKAY)
 		{
-			ReportResultError(connection, result, WARNING);
-			PQclear(result);
-
 			/* cannot recover this transaction right now */
 			continue;
 		}

src/include/distributed/remote_commands.h

@@ -13,6 +13,9 @@
 
 #include "distributed/connection_management.h"
 
+/* errors which ExecuteRemoteCommand might return */
+#define QUERY_SEND_FAILED 1
+#define RESPONSE_NOT_OKAY 2
 
 struct pg_result; /* target of the PGresult typedef */
 
@@ -34,6 +37,9 @@ extern void LogRemoteCommand(MultiConnection *connection, const char *command);
 /* wrappers around libpq functions, with command logging support */
 extern void ExecuteCriticalRemoteCommand(MultiConnection *connection,
 										 const char *command);
+extern int ExecuteOptionalRemoteCommand(MultiConnection *connection,
+										const char *command,
+										PGresult **result);
 extern int SendRemoteCommand(MultiConnection *connection, const char *command);
 extern int SendRemoteCommandParams(MultiConnection *connection, const char *command,
 								   int parameterCount, const Oid *parameterTypes,