Attached is a patch that replaces a bunch of places where StringInfos

are unnecessarily allocated on the heap rather than the stack. If the
StringInfo doesn't outlive the stack frame in which it is created,
there is no need to allocate it on the heap via makeStringInfo() --
stack allocation is faster.  While it's not a big deal unless the
code is in a critical path, I don't see a reason not to save a few
cycles -- using stack allocation is not less readable.

I also cleaned up a bit of code along the way: moved variable
declarations into a more tightly-enclosing scope where possible,
fixed some pointless copying of strings in dblink, etc.

1 files changed, 58 insertions, 67 deletions

diff --git a/contrib/dblink/dblink.c b/contrib/dblink/dblink.c
index 4fd17c32271..b1b863ea1e4 100644
--- a/contrib/dblink/dblink.c
+++ b/contrib/dblink/dblink.c
@@ -301,11 +301,12 @@ dblink_open(PG_FUNCTION_ARGS)
 	char	   *curname = NULL;
 	char	   *sql = NULL;
 	char	   *conname = NULL;
-	StringInfo	str = makeStringInfo();
+	StringInfoData buf;
 	remoteConn *rconn = NULL;
 	bool		fail = true;	/* default to backward compatible behavior */
 
 	DBLINK_INIT;
+	initStringInfo(&buf);
 
 	if (PG_NARGS() == 2)
 	{
@@ -361,8 +362,8 @@ dblink_open(PG_FUNCTION_ARGS)
 	if (rconn->newXactForCursor)
 		(rconn->openCursorCount)++;
 
-	appendStringInfo(str, "DECLARE %s CURSOR FOR %s", curname, sql);
-	res = PQexec(conn, str->data);
+	appendStringInfo(&buf, "DECLARE %s CURSOR FOR %s", curname, sql);
+	res = PQexec(conn, buf.data);
 	if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
 	{
 		if (fail)
@@ -389,12 +390,13 @@ dblink_close(PG_FUNCTION_ARGS)
 	PGresult   *res = NULL;
 	char	   *curname = NULL;
 	char	   *conname = NULL;
-	StringInfo	str = makeStringInfo();
+	StringInfoData buf;
 	char	   *msg;
 	remoteConn *rconn = NULL;
 	bool		fail = true;	/* default to backward compatible behavior */
 
 	DBLINK_INIT;
+	initStringInfo(&buf);
 
 	if (PG_NARGS() == 1)
 	{
@@ -432,10 +434,10 @@ dblink_close(PG_FUNCTION_ARGS)
 	else
 		conn = rconn->conn;
 
-	appendStringInfo(str, "CLOSE %s", curname);
+	appendStringInfo(&buf, "CLOSE %s", curname);
 
 	/* close the cursor */
-	res = PQexec(conn, str->data);
+	res = PQexec(conn, buf.data);
 	if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
 	{
 		if (fail)
@@ -493,7 +495,7 @@ dblink_fetch(PG_FUNCTION_ARGS)
 	if (SRF_IS_FIRSTCALL())
 	{
 		PGconn	   *conn = NULL;
-		StringInfo	str = makeStringInfo();
+		StringInfoData buf;
 		char	   *curname = NULL;
 		int			howmany = 0;
 		bool		fail = true;	/* default to backward compatible */
@@ -542,6 +544,9 @@ dblink_fetch(PG_FUNCTION_ARGS)
 		if (!conn)
 			DBLINK_CONN_NOT_AVAIL;
 
+		initStringInfo(&buf);
+		appendStringInfo(&buf, "FETCH %d FROM %s", howmany, curname);
+
 		/* create a function context for cross-call persistence */
 		funcctx = SRF_FIRSTCALL_INIT();
 
@@ -550,9 +555,7 @@ dblink_fetch(PG_FUNCTION_ARGS)
 		 */
 		oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
 
-		appendStringInfo(str, "FETCH %d FROM %s", howmany, curname);
-
-		res = PQexec(conn, str->data);
+		res = PQexec(conn, buf.data);
 		if (!res ||
 			(PQresultStatus(res) != PGRES_COMMAND_OK &&
 			 PQresultStatus(res) != PGRES_TUPLES_OK))
@@ -1547,13 +1550,14 @@ get_sql_insert(Oid relid, int2vector *pkattnums, int16 pknumatts, char **src_pka
 	HeapTuple	tuple;
 	TupleDesc	tupdesc;
 	int			natts;
-	StringInfo	str = makeStringInfo();
-	char	   *sql;
+	StringInfoData buf;
 	char	   *val;
 	int16		key;
 	int			i;
 	bool		needComma;
 
+	initStringInfo(&buf);
+
 	/* get relation name including any needed schema prefix and quoting */
 	relname = generate_relation_name(relid);
 
@@ -1570,7 +1574,7 @@ get_sql_insert(Oid relid, int2vector *pkattnums, int16 pknumatts, char **src_pka
 				(errcode(ERRCODE_CARDINALITY_VIOLATION),
 				 errmsg("source row not found")));
 
-	appendStringInfo(str, "INSERT INTO %s(", relname);
+	appendStringInfo(&buf, "INSERT INTO %s(", relname);
 
 	needComma = false;
 	for (i = 0; i < natts; i++)
@@ -1579,14 +1583,14 @@ get_sql_insert(Oid relid, int2vector *pkattnums, int16 pknumatts, char **src_pka
 			continue;
 
 		if (needComma)
-			appendStringInfo(str, ",");
+			appendStringInfo(&buf, ",");
 
-		appendStringInfo(str, "%s",
+		appendStringInfoString(&buf,
 					  quote_ident_cstr(NameStr(tupdesc->attrs[i]->attname)));
 		needComma = true;
 	}
 
-	appendStringInfo(str, ") VALUES(");
+	appendStringInfo(&buf, ") VALUES(");
 
 	/*
 	 * remember attvals are 1 based
@@ -1598,7 +1602,7 @@ get_sql_insert(Oid relid, int2vector *pkattnums, int16 pknumatts, char **src_pka
 			continue;
 
 		if (needComma)
-			appendStringInfo(str, ",");
+			appendStringInfo(&buf, ",");
 
 		if (tgt_pkattvals != NULL)
 			key = get_attnum_pk_pos(pkattnums, pknumatts, i + 1);
@@ -1612,21 +1616,17 @@ get_sql_insert(Oid relid, int2vector *pkattnums, int16 pknumatts, char **src_pka
 
 		if (val != NULL)
 		{
-			appendStringInfo(str, "%s", quote_literal_cstr(val));
+			appendStringInfoString(&buf, quote_literal_cstr(val));
 			pfree(val);
 		}
 		else
-			appendStringInfo(str, "NULL");
+			appendStringInfo(&buf, "NULL");
 		needComma = true;
 	}
-	appendStringInfo(str, ")");
+	appendStringInfo(&buf, ")");
 
-	sql = pstrdup(str->data);
-	pfree(str->data);
-	pfree(str);
 	relation_close(rel, AccessShareLock);
-
-	return (sql);
+	return (buf.data);
 }
 
 static char *
@@ -1636,10 +1636,11 @@ get_sql_delete(Oid relid, int2vector *pkattnums, int16 pknumatts, char **tgt_pka
 	char	   *relname;
 	TupleDesc	tupdesc;
 	int			natts;
-	StringInfo	str = makeStringInfo();
-	char	   *sql;
+	StringInfoData	buf;
 	int			i;
 
+	initStringInfo(&buf);
+
 	/* get relation name including any needed schema prefix and quoting */
 	relname = generate_relation_name(relid);
 
@@ -1650,15 +1651,15 @@ get_sql_delete(Oid relid, int2vector *pkattnums, int16 pknumatts, char **tgt_pka
 	tupdesc = rel->rd_att;
 	natts = tupdesc->natts;
 
-	appendStringInfo(str, "DELETE FROM %s WHERE ", relname);
+	appendStringInfo(&buf, "DELETE FROM %s WHERE ", relname);
 	for (i = 0; i < pknumatts; i++)
 	{
 		int16		pkattnum = pkattnums->values[i];
 
 		if (i > 0)
-			appendStringInfo(str, " AND ");
+			appendStringInfo(&buf, " AND ");
 
-		appendStringInfo(str, "%s",
+		appendStringInfoString(&buf,
 		   quote_ident_cstr(NameStr(tupdesc->attrs[pkattnum - 1]->attname)));
 
 		if (tgt_pkattvals == NULL)
@@ -1666,18 +1667,14 @@ get_sql_delete(Oid relid, int2vector *pkattnums, int16 pknumatts, char **tgt_pka
 			elog(ERROR, "target key array must not be NULL");
 
 		if (tgt_pkattvals[i] != NULL)
-			appendStringInfo(str, " = %s",
+			appendStringInfo(&buf, " = %s",
 							 quote_literal_cstr(tgt_pkattvals[i]));
 		else
-			appendStringInfo(str, " IS NULL");
+			appendStringInfo(&buf, " IS NULL");
 	}
 
-	sql = pstrdup(str->data);
-	pfree(str->data);
-	pfree(str);
 	relation_close(rel, AccessShareLock);
-
-	return (sql);
+	return (buf.data);
 }
 
 static char *
@@ -1688,13 +1685,14 @@ get_sql_update(Oid relid, int2vector *pkattnums, int16 pknumatts, char **src_pka
 	HeapTuple	tuple;
 	TupleDesc	tupdesc;
 	int			natts;
-	StringInfo	str = makeStringInfo();
-	char	   *sql;
+	StringInfoData buf;
 	char	   *val;
 	int16		key;
 	int			i;
 	bool		needComma;
 
+	initStringInfo(&buf);
+
 	/* get relation name including any needed schema prefix and quoting */
 	relname = generate_relation_name(relid);
 
@@ -1711,7 +1709,7 @@ get_sql_update(Oid relid, int2vector *pkattnums, int16 pknumatts, char **src_pka
 				(errcode(ERRCODE_CARDINALITY_VIOLATION),
 				 errmsg("source row not found")));
 
-	appendStringInfo(str, "UPDATE %s SET ", relname);
+	appendStringInfo(&buf, "UPDATE %s SET ", relname);
 
 	needComma = false;
 	for (i = 0; i < natts; i++)
@@ -1720,9 +1718,9 @@ get_sql_update(Oid relid, int2vector *pkattnums, int16 pknumatts, char **src_pka
 			continue;
 
 		if (needComma)
-			appendStringInfo(str, ", ");
+			appendStringInfo(&buf, ", ");
 
-		appendStringInfo(str, "%s = ",
+		appendStringInfo(&buf, "%s = ",
 					  quote_ident_cstr(NameStr(tupdesc->attrs[i]->attname)));
 
 		if (tgt_pkattvals != NULL)
@@ -1737,24 +1735,24 @@ get_sql_update(Oid relid, int2vector *pkattnums, int16 pknumatts, char **src_pka
 
 		if (val != NULL)
 		{
-			appendStringInfo(str, "%s", quote_literal_cstr(val));
+			appendStringInfoString(&buf, quote_literal_cstr(val));
 			pfree(val);
 		}
 		else
-			appendStringInfo(str, "NULL");
+			appendStringInfoString(&buf, "NULL");
 		needComma = true;
 	}
 
-	appendStringInfo(str, " WHERE ");
+	appendStringInfo(&buf, " WHERE ");
 
 	for (i = 0; i < pknumatts; i++)
 	{
 		int16		pkattnum = pkattnums->values[i];
 
 		if (i > 0)
-			appendStringInfo(str, " AND ");
+			appendStringInfo(&buf, " AND ");
 
-		appendStringInfo(str, "%s",
+		appendStringInfo(&buf, "%s",
 		   quote_ident_cstr(NameStr(tupdesc->attrs[pkattnum - 1]->attname)));
 
 		if (tgt_pkattvals != NULL)
@@ -1764,19 +1762,15 @@ get_sql_update(Oid relid, int2vector *pkattnums, int16 pknumatts, char **src_pka
 
 		if (val != NULL)
 		{
-			appendStringInfo(str, " = %s", quote_literal_cstr(val));
+			appendStringInfo(&buf, " = %s", quote_literal_cstr(val));
 			pfree(val);
 		}
 		else
-			appendStringInfo(str, " IS NULL");
+			appendStringInfo(&buf, " IS NULL");
 	}
 
-	sql = pstrdup(str->data);
-	pfree(str->data);
-	pfree(str);
 	relation_close(rel, AccessShareLock);
-
-	return (sql);
+	return (buf.data);
 }
 
 /*
@@ -1836,12 +1830,13 @@ get_tuple_of_interest(Oid relid, int2vector *pkattnums, int16 pknumatts, char **
 	Relation	rel;
 	char	   *relname;
 	TupleDesc	tupdesc;
-	StringInfo	str = makeStringInfo();
-	char	   *sql = NULL;
+	StringInfoData buf;
 	int			ret;
 	HeapTuple	tuple;
 	int			i;
 
+	initStringInfo(&buf);
+
 	/* get relation name including any needed schema prefix and quoting */
 	relname = generate_relation_name(relid);
 
@@ -1863,34 +1858,30 @@ get_tuple_of_interest(Oid relid, int2vector *pkattnums, int16 pknumatts, char **
 	 * Build sql statement to look up tuple of interest Use src_pkattvals as
 	 * the criteria.
 	 */
-	appendStringInfo(str, "SELECT * FROM %s WHERE ", relname);
+	appendStringInfo(&buf, "SELECT * FROM %s WHERE ", relname);
 
 	for (i = 0; i < pknumatts; i++)
 	{
 		int16		pkattnum = pkattnums->values[i];
 
 		if (i > 0)
-			appendStringInfo(str, " AND ");
+			appendStringInfo(&buf, " AND ");
 
-		appendStringInfo(str, "%s",
+		appendStringInfoString(&buf,
 		   quote_ident_cstr(NameStr(tupdesc->attrs[pkattnum - 1]->attname)));
 
 		if (src_pkattvals[i] != NULL)
-			appendStringInfo(str, " = %s",
+			appendStringInfo(&buf, " = %s",
 							 quote_literal_cstr(src_pkattvals[i]));
 		else
-			appendStringInfo(str, " IS NULL");
+			appendStringInfo(&buf, " IS NULL");
 	}
 
-	sql = pstrdup(str->data);
-	pfree(str->data);
-	pfree(str);
-
 	/*
 	 * Retrieve the desired tuple
 	 */
-	ret = SPI_exec(sql, 0);
-	pfree(sql);
+	ret = SPI_exec(buf.data, 0);
+	pfree(buf.data);
 
 	/*
 	 * Only allow one qualifying tuple