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.

2 files changed, 39 insertions, 40 deletions

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 755a64a9446..767d4c9f806 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994-5, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.144 2006/02/28 04:10:27 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.145 2006/03/01 06:51:01 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -232,7 +232,7 @@ ExplainOnePlan(QueryDesc *queryDesc, ExplainStmt *stmt,
 	instr_time	starttime;
 	double		totaltime = 0;
 	ExplainState *es;
-	StringInfo	str;
+	StringInfoData buf;
 	int			eflags;
 
 	INSTR_TIME_SET_CURRENT(starttime);
@@ -285,9 +285,8 @@ ExplainOnePlan(QueryDesc *queryDesc, ExplainStmt *stmt,
 		}
 	}
 
-	str = makeStringInfo();
-
-	explain_outNode(str, queryDesc->plantree, queryDesc->planstate,
+	initStringInfo(&buf);
+	explain_outNode(&buf, queryDesc->plantree, queryDesc->planstate,
 					NULL, 0, es);
 
 	/*
@@ -335,18 +334,18 @@ ExplainOnePlan(QueryDesc *queryDesc, ExplainStmt *stmt,
 				if (trig->tgisconstraint &&
 				(conname = GetConstraintNameForTrigger(trig->tgoid)) != NULL)
 				{
-					appendStringInfo(str, "Trigger for constraint %s",
+					appendStringInfo(&buf, "Trigger for constraint %s",
 									 conname);
 					pfree(conname);
 				}
 				else
-					appendStringInfo(str, "Trigger %s", trig->tgname);
+					appendStringInfo(&buf, "Trigger %s", trig->tgname);
 
 				if (numrels > 1)
-					appendStringInfo(str, " on %s",
+					appendStringInfo(&buf, " on %s",
 							RelationGetRelationName(rInfo->ri_RelationDesc));
 
-				appendStringInfo(str, ": time=%.3f calls=%.0f\n",
+				appendStringInfo(&buf, ": time=%.3f calls=%.0f\n",
 								 1000.0 * instr->total,
 								 instr->ntuples);
 			}
@@ -370,12 +369,11 @@ ExplainOnePlan(QueryDesc *queryDesc, ExplainStmt *stmt,
 	totaltime += elapsed_time(&starttime);
 
 	if (stmt->analyze)
-		appendStringInfo(str, "Total runtime: %.3f ms\n",
+		appendStringInfo(&buf, "Total runtime: %.3f ms\n",
 						 1000.0 * totaltime);
-	do_text_output_multiline(tstate, str->data);
+	do_text_output_multiline(tstate, buf.data);
 
-	pfree(str->data);
-	pfree(str);
+	pfree(buf.data);
 	pfree(es);
 }
 
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index c2119edcecc..cbfcf52ffe3 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/varlena.c,v 1.143 2006/02/26 02:23:41 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/varlena.c,v 1.144 2006/03/01 06:51:01 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2038,7 +2038,7 @@ replace_text(PG_FUNCTION_ARGS)
 	text	   *buf_text;
 	text	   *ret_text;
 	int			curr_posn;
-	StringInfo	str;
+	StringInfoData str;
 
 	if (src_text_len == 0 || from_sub_text_len == 0)
 		PG_RETURN_TEXT_P(src_text);
@@ -2049,7 +2049,7 @@ replace_text(PG_FUNCTION_ARGS)
 	if (curr_posn == 0)
 		PG_RETURN_TEXT_P(src_text);
 
-	str = makeStringInfo();
+	initStringInfo(&str);
 	buf_text = src_text;
 
 	while (curr_posn > 0)
@@ -2059,8 +2059,8 @@ replace_text(PG_FUNCTION_ARGS)
 		right_text = text_substring(PointerGetDatum(buf_text),
 									curr_posn + from_sub_text_len, -1, true);
 
-		appendStringInfoText(str, left_text);
-		appendStringInfoText(str, to_sub_text);
+		appendStringInfoText(&str, left_text);
+		appendStringInfoText(&str, to_sub_text);
 
 		if (buf_text != src_text)
 			pfree(buf_text);
@@ -2069,13 +2069,12 @@ replace_text(PG_FUNCTION_ARGS)
 		curr_posn = TEXTPOS(buf_text, from_sub_text);
 	}
 
-	appendStringInfoText(str, buf_text);
+	appendStringInfoText(&str, buf_text);
 	if (buf_text != src_text)
 		pfree(buf_text);
 
-	ret_text = PG_STR_GET_TEXT(str->data);
-	pfree(str->data);
-	pfree(str);
+	ret_text = PG_STR_GET_TEXT(str.data);
+	pfree(str.data);
 
 	PG_RETURN_TEXT_P(ret_text);
 }
@@ -2227,8 +2226,7 @@ replace_text_regexp(text *src_text, void *regexp,
 	text	   *ret_text;
 	regex_t    *re = (regex_t *) regexp;
 	int			src_text_len = VARSIZE(src_text) - VARHDRSZ;
-	StringInfo	str = makeStringInfo();
-	int			regexec_result;
+	StringInfoData	buf;
 	regmatch_t	pmatch[REGEXP_REPLACE_BACKREF_CNT];
 	pg_wchar   *data;
 	size_t		data_len;
@@ -2236,6 +2234,8 @@ replace_text_regexp(text *src_text, void *regexp,
 	int			data_pos;
 	bool		have_escape;
 
+	initStringInfo(&buf);
+
 	/* Convert data string to wide characters. */
 	data = (pg_wchar *) palloc((src_text_len + 1) * sizeof(pg_wchar));
 	data_len = pg_mb2wchar_with_len(VARDATA(src_text), data, src_text_len);
@@ -2245,6 +2245,8 @@ replace_text_regexp(text *src_text, void *regexp,
 
 	for (search_start = data_pos = 0; search_start <= data_len;)
 	{
+		int regexec_result;
+
 		regexec_result = pg_regexec(re,
 									data,
 									data_len,
@@ -2254,20 +2256,19 @@ replace_text_regexp(text *src_text, void *regexp,
 									pmatch,
 									0);
 
-		if (regexec_result != REG_OKAY && regexec_result != REG_NOMATCH)
+		if (regexec_result == REG_NOMATCH)
+			break;
+
+		if (regexec_result != REG_OKAY)
 		{
 			char		errMsg[100];
 
-			/* re failed??? */
 			pg_regerror(regexec_result, re, errMsg, sizeof(errMsg));
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_REGULAR_EXPRESSION),
 					 errmsg("regular expression failed: %s", errMsg)));
 		}
 
-		if (regexec_result == REG_NOMATCH)
-			break;
-
 		/*
 		 * Copy the text to the left of the match position.  Because we are
 		 * working with character not byte indexes, it's easiest to use
@@ -2281,7 +2282,7 @@ replace_text_regexp(text *src_text, void *regexp,
 									   data_pos + 1,
 									   pmatch[0].rm_so - data_pos,
 									   false);
-			appendStringInfoText(str, left_text);
+			appendStringInfoText(&buf, left_text);
 			pfree(left_text);
 		}
 
@@ -2290,9 +2291,9 @@ replace_text_regexp(text *src_text, void *regexp,
 		 * replace_text has escape characters.
 		 */
 		if (have_escape)
-			appendStringInfoRegexpSubstr(str, replace_text, pmatch, src_text);
+			appendStringInfoRegexpSubstr(&buf, replace_text, pmatch, src_text);
 		else
-			appendStringInfoText(str, replace_text);
+			appendStringInfoText(&buf, replace_text);
 
 		search_start = data_pos = pmatch[0].rm_eo;
 
@@ -2318,13 +2319,12 @@ replace_text_regexp(text *src_text, void *regexp,
 
 		right_text = text_substring(PointerGetDatum(src_text),
 									data_pos + 1, -1, true);
-		appendStringInfoText(str, right_text);
+		appendStringInfoText(&buf, right_text);
 		pfree(right_text);
 	}
 
-	ret_text = PG_STR_GET_TEXT(str->data);
-	pfree(str->data);
-	pfree(str);
+	ret_text = PG_STR_GET_TEXT(buf.data);
+	pfree(buf.data);
 	pfree(data);
 
 	return ret_text;
@@ -2512,7 +2512,7 @@ array_to_text(PG_FUNCTION_ARGS)
 	int			typlen;
 	bool		typbyval;
 	char		typalign;
-	StringInfo	result_str = makeStringInfo();
+	StringInfoData	buf;
 	bool		printed = false;
 	char	   *p;
 	bits8	   *bitmap;
@@ -2529,6 +2529,7 @@ array_to_text(PG_FUNCTION_ARGS)
 		PG_RETURN_TEXT_P(PG_STR_GET_TEXT(""));
 
 	element_type = ARR_ELEMTYPE(v);
+	initStringInfo(&buf);
 
 	/*
 	 * We arrange to look up info about element type, including its output
@@ -2583,9 +2584,9 @@ array_to_text(PG_FUNCTION_ARGS)
 												  itemvalue));
 
 			if (printed)
-				appendStringInfo(result_str, "%s%s", fldsep, value);
+				appendStringInfo(&buf, "%s%s", fldsep, value);
 			else
-				appendStringInfoString(result_str, value);
+				appendStringInfoString(&buf, value);
 			printed = true;
 
 			p = att_addlength(p, typlen, PointerGetDatum(p));
@@ -2604,7 +2605,7 @@ array_to_text(PG_FUNCTION_ARGS)
 		}
 	}
 
-	PG_RETURN_TEXT_P(PG_STR_GET_TEXT(result_str->data));
+	PG_RETURN_TEXT_P(PG_STR_GET_TEXT(buf.data));
 }
 
 #define HEXBASE 16