Reap the benefits of not having to avoid leaking PGresults.

Remove a bunch of PG_TRY constructs, de-volatilize related
variables, remove some PQclear calls in error paths.
Aside from making the code simpler and shorter, this should
provide some marginal performance gains.

For ease of review, I did not re-indent code within the removed
PG_TRY constructs.  That'll be done in a separate patch.

Author: Tom Lane <[email protected]>
Reviewed-by: Matheus Alcantara <[email protected]>
Discussion: https://postgr.es/m/[email protected]

Author: tglsfdc

contrib/dblink/dblink.c

@@ -101,8 +101,8 @@ static void materializeQueryResult(FunctionCallInfo fcinfo,
 								   const char *conname,
 								   const char *sql,
 								   bool fail);
-static PGresult *storeQueryResult(volatile storeInfo *sinfo, PGconn *conn, const char *sql);
-static void storeRow(volatile storeInfo *sinfo, PGresult *res, bool first);
+static PGresult *storeQueryResult(storeInfo *sinfo, PGconn *conn, const char *sql);
+static void storeRow(storeInfo *sinfo, PGresult *res, bool first);
 static remoteConn *getConnectionByName(const char *name);
 static HTAB *createConnHash(void);
 static remoteConn *createNewConnection(const char *name);
@@ -169,14 +169,6 @@ typedef struct remoteConnHashEnt
 /* initial number of connection hashes */
 #define NUMCONN 16
 
-static char *
-xpstrdup(const char *in)
-{
-	if (in == NULL)
-		return NULL;
-	return pstrdup(in);
-}
-
 pg_noreturn static void
 dblink_res_internalerror(PGconn *conn, PGresult *res, const char *p2)
 {
@@ -870,17 +862,14 @@ static void
 materializeResult(FunctionCallInfo fcinfo, PGconn *conn, PGresult *res)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+	TupleDesc	tupdesc;
+	bool		is_sql_cmd;
+	int			ntuples;
+	int			nfields;
 
 	/* prepTuplestoreResult must have been called previously */
 	Assert(rsinfo->returnMode == SFRM_Materialize);
 
-	PG_TRY();
-	{
-		TupleDesc	tupdesc;
-		bool		is_sql_cmd;
-		int			ntuples;
-		int			nfields;
-
 		if (PQresultStatus(res) == PGRES_COMMAND_OK)
 		{
 			is_sql_cmd = true;
@@ -988,13 +977,8 @@ materializeResult(FunctionCallInfo fcinfo, PGconn *conn, PGresult *res)
 			/* clean up GUC settings, if we changed any */
 			restoreLocalGucs(nestlevel);
 		}
-	}
-	PG_FINALLY();
-	{
-		/* be sure to release the libpq result */
+
 		PQclear(res);
-	}
-	PG_END_TRY();
 }
 
 /*
@@ -1013,16 +997,17 @@ materializeQueryResult(FunctionCallInfo fcinfo,
 					   bool fail)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
-	PGresult   *volatile res = NULL;
-	volatile storeInfo sinfo = {0};
 
 	/* prepTuplestoreResult must have been called previously */
 	Assert(rsinfo->returnMode == SFRM_Materialize);
 
-	sinfo.fcinfo = fcinfo;
-
+	/* Use a PG_TRY block to ensure we pump libpq dry of results */
 	PG_TRY();
 	{
+		storeInfo	sinfo = {0};
+		PGresult   *res;
+
+		sinfo.fcinfo = fcinfo;
 		/* Create short-lived memory context for data conversions */
 		sinfo.tmpcontext = AllocSetContextCreate(CurrentMemoryContext,
 												 "dblink temporary context",
@@ -1035,14 +1020,7 @@ materializeQueryResult(FunctionCallInfo fcinfo,
 			(PQresultStatus(res) != PGRES_COMMAND_OK &&
 			 PQresultStatus(res) != PGRES_TUPLES_OK))
 		{
-			/*
-			 * dblink_res_error will clear the passed PGresult, so we need
-			 * this ugly dance to avoid doing so twice during error exit
-			 */
-			PGresult   *res1 = res;
-
-			res = NULL;
-			dblink_res_error(conn, conname, res1, fail,
+			dblink_res_error(conn, conname, res, fail,
 							 "while executing query");
 			/* if fail isn't set, we'll return an empty query result */
 		}
@@ -1081,7 +1059,6 @@ materializeQueryResult(FunctionCallInfo fcinfo,
 			tuplestore_puttuple(tupstore, tuple);
 
 			PQclear(res);
-			res = NULL;
 		}
 		else
 		{
@@ -1090,26 +1067,20 @@ materializeQueryResult(FunctionCallInfo fcinfo,
 			Assert(rsinfo->setResult != NULL);
 
 			PQclear(res);
-			res = NULL;
 		}
 
 		/* clean up data conversion short-lived memory context */
 		if (sinfo.tmpcontext != NULL)
 			MemoryContextDelete(sinfo.tmpcontext);
-		sinfo.tmpcontext = NULL;
 
 		PQclear(sinfo.last_res);
-		sinfo.last_res = NULL;
 		PQclear(sinfo.cur_res);
-		sinfo.cur_res = NULL;
 	}
 	PG_CATCH();
 	{
-		/* be sure to release any libpq result we collected */
-		PQclear(res);
-		PQclear(sinfo.last_res);
-		PQclear(sinfo.cur_res);
-		/* and clear out any pending data in libpq */
+		PGresult   *res;
+
+		/* be sure to clear out any pending data in libpq */
 		while ((res = libpqsrv_get_result(conn, dblink_we_get_result)) !=
 			   NULL)
 			PQclear(res);
@@ -1122,7 +1093,7 @@ materializeQueryResult(FunctionCallInfo fcinfo,
  * Execute query, and send any result rows to sinfo->tuplestore.
  */
 static PGresult *
-storeQueryResult(volatile storeInfo *sinfo, PGconn *conn, const char *sql)
+storeQueryResult(storeInfo *sinfo, PGconn *conn, const char *sql)
 {
 	bool		first = true;
 	int			nestlevel = -1;
@@ -1190,7 +1161,7 @@ storeQueryResult(volatile storeInfo *sinfo, PGconn *conn, const char *sql)
  * (in this case the PGresult might contain either zero or one row).
  */
 static void
-storeRow(volatile storeInfo *sinfo, PGresult *res, bool first)
+storeRow(storeInfo *sinfo, PGresult *res, bool first)
 {
 	int			nfields = PQnfields(res);
 	HeapTuple	tuple;
@@ -2795,26 +2766,25 @@ dblink_connstr_check(const char *connstr)
 /*
  * Report an error received from the remote server
  *
- * res: the received error result (will be freed)
+ * res: the received error result
  * fail: true for ERROR ereport, false for NOTICE
  * fmt and following args: sprintf-style format and values for errcontext;
  * the resulting string should be worded like "while <some action>"
+ *
+ * If "res" is not NULL, it'll be PQclear'ed here (unless we throw error,
+ * in which case memory context cleanup will clear it eventually).
  */
 static void
 dblink_res_error(PGconn *conn, const char *conname, PGresult *res,
 				 bool fail, const char *fmt,...)
 {
 	int			level;
 	char	   *pg_diag_sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE);
-	char	   *pg_diag_message_primary = PQresultErrorField(res, PG_DIAG_MESSAGE_PRIMARY);
-	char	   *pg_diag_message_detail = PQresultErrorField(res, PG_DIAG_MESSAGE_DETAIL);
-	char	   *pg_diag_message_hint = PQresultErrorField(res, PG_DIAG_MESSAGE_HINT);
-	char	   *pg_diag_context = PQresultErrorField(res, PG_DIAG_CONTEXT);
+	char	   *message_primary = PQresultErrorField(res, PG_DIAG_MESSAGE_PRIMARY);
+	char	   *message_detail = PQresultErrorField(res, PG_DIAG_MESSAGE_DETAIL);
+	char	   *message_hint = PQresultErrorField(res, PG_DIAG_MESSAGE_HINT);
+	char	   *message_context = PQresultErrorField(res, PG_DIAG_CONTEXT);
 	int			sqlstate;
-	char	   *message_primary;
-	char	   *message_detail;
-	char	   *message_hint;
-	char	   *message_context;
 	va_list		ap;
 	char		dblink_context_msg[512];
 
@@ -2832,11 +2802,6 @@ dblink_res_error(PGconn *conn, const char *conname, PGresult *res,
 	else
 		sqlstate = ERRCODE_CONNECTION_FAILURE;
 
-	message_primary = xpstrdup(pg_diag_message_primary);
-	message_detail = xpstrdup(pg_diag_message_detail);
-	message_hint = xpstrdup(pg_diag_message_hint);
-	message_context = xpstrdup(pg_diag_context);
-
 	/*
 	 * If we don't get a message from the PGresult, try the PGconn.  This is
 	 * needed because for connection-level failures, PQgetResult may just
@@ -2845,14 +2810,6 @@ dblink_res_error(PGconn *conn, const char *conname, PGresult *res,
 	if (message_primary == NULL)
 		message_primary = pchomp(PQerrorMessage(conn));
 
-	/*
-	 * Now that we've copied all the data we need out of the PGresult, it's
-	 * safe to free it.  We must do this to avoid PGresult leakage.  We're
-	 * leaking all the strings too, but those are in palloc'd memory that will
-	 * get cleaned up eventually.
-	 */
-	PQclear(res);
-
 	/*
 	 * Format the basic errcontext string.  Below, we'll add on something
 	 * about the connection name.  That's a violation of the translatability
@@ -2877,6 +2834,7 @@ dblink_res_error(PGconn *conn, const char *conname, PGresult *res,
 						 dblink_context_msg, conname)) :
 			 (errcontext("%s on unnamed dblink connection",
 						 dblink_context_msg))));
+	PQclear(res);
 }
 
 /*

contrib/postgres_fdw/connection.c

@@ -815,7 +815,7 @@ static void
 do_sql_command_begin(PGconn *conn, const char *sql)
 {
 	if (!PQsendQuery(conn, sql))
-		pgfdw_report_error(ERROR, NULL, conn, false, sql);
+		pgfdw_report_error(ERROR, NULL, conn, sql);
 }
 
 static void
@@ -830,10 +830,10 @@ do_sql_command_end(PGconn *conn, const char *sql, bool consume_input)
 	 * would be large compared to the overhead of PQconsumeInput.)
 	 */
 	if (consume_input && !PQconsumeInput(conn))
-		pgfdw_report_error(ERROR, NULL, conn, false, sql);
+		pgfdw_report_error(ERROR, NULL, conn, sql);
 	res = pgfdw_get_result(conn);
 	if (PQresultStatus(res) != PGRES_COMMAND_OK)
-		pgfdw_report_error(ERROR, res, conn, true, sql);
+		pgfdw_report_error(ERROR, res, conn, sql);
 	PQclear(res);
 }
 
@@ -967,22 +967,21 @@ pgfdw_get_result(PGconn *conn)
  * Report an error we got from the remote server.
  *
  * elevel: error level to use (typically ERROR, but might be less)
- * res: PGresult containing the error
+ * res: PGresult containing the error (might be NULL)
  * conn: connection we did the query on
- * clear: if true, PQclear the result (otherwise caller will handle it)
  * sql: NULL, or text of remote command we tried to execute
  *
+ * If "res" is not NULL, it'll be PQclear'ed here (unless we throw error,
+ * in which case memory context cleanup will clear it eventually).
+ *
  * Note: callers that choose not to throw ERROR for a remote error are
  * responsible for making sure that the associated ConnCacheEntry gets
  * marked with have_error = true.
  */
 void
 pgfdw_report_error(int elevel, PGresult *res, PGconn *conn,
-				   bool clear, const char *sql)
+				   const char *sql)
 {
-	/* If requested, PGresult must be released before leaving this function. */
-	PG_TRY();
-	{
 		char	   *diag_sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE);
 		char	   *message_primary = PQresultErrorField(res, PG_DIAG_MESSAGE_PRIMARY);
 		char	   *message_detail = PQresultErrorField(res, PG_DIAG_MESSAGE_DETAIL);
@@ -1016,13 +1015,7 @@ pgfdw_report_error(int elevel, PGresult *res, PGconn *conn,
 				 message_hint ? errhint("%s", message_hint) : 0,
 				 message_context ? errcontext("%s", message_context) : 0,
 				 sql ? errcontext("remote SQL command: %s", sql) : 0));
-	}
-	PG_FINALLY();
-	{
-		if (clear)
 			PQclear(res);
-	}
-	PG_END_TRY();
 }
 
 /*
@@ -1545,7 +1538,7 @@ pgfdw_exec_cleanup_query_begin(PGconn *conn, const char *query)
 	 */
 	if (!PQsendQuery(conn, query))
 	{
-		pgfdw_report_error(WARNING, NULL, conn, false, query);
+		pgfdw_report_error(WARNING, NULL, conn, query);
 		return false;
 	}
 
@@ -1570,7 +1563,7 @@ pgfdw_exec_cleanup_query_end(PGconn *conn, const char *query,
 	 */
 	if (consume_input && !PQconsumeInput(conn))
 	{
-		pgfdw_report_error(WARNING, NULL, conn, false, query);
+		pgfdw_report_error(WARNING, NULL, conn, query);
 		return false;
 	}
 
@@ -1582,15 +1575,15 @@ pgfdw_exec_cleanup_query_end(PGconn *conn, const char *query,
 					(errmsg("could not get query result due to timeout"),
 					 errcontext("remote SQL command: %s", query)));
 		else
-			pgfdw_report_error(WARNING, NULL, conn, false, query);
+			pgfdw_report_error(WARNING, NULL, conn, query);
 
 		return false;
 	}
 
 	/* Issue a warning if not successful. */
 	if (PQresultStatus(result) != PGRES_COMMAND_OK)
 	{
-		pgfdw_report_error(WARNING, result, conn, true, query);
+		pgfdw_report_error(WARNING, result, conn, query);
 		return ignore_errors;
 	}
 	PQclear(result);
@@ -1618,17 +1611,12 @@ pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime,
 						 PGresult **result,
 						 bool *timed_out)
 {
-	volatile bool failed = false;
-	PGresult   *volatile last_res = NULL;
+	bool		failed = false;
+	PGresult   *last_res = NULL;
+	int			canceldelta = RETRY_CANCEL_TIMEOUT * 2;
 
 	*result = NULL;
 	*timed_out = false;
-
-	/* In what follows, do not leak any PGresults on an error. */
-	PG_TRY();
-	{
-		int			canceldelta = RETRY_CANCEL_TIMEOUT * 2;
-
 		for (;;)
 		{
 			PGresult   *res;
@@ -1706,15 +1694,7 @@ pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime,
 			PQclear(last_res);
 			last_res = res;
 		}
-exit:	;
-	}
-	PG_CATCH();
-	{
-		PQclear(last_res);
-		PG_RE_THROW();
-	}
-	PG_END_TRY();
-
+exit:
 	if (failed)
 		PQclear(last_res);
 	else