Optmize query denormalization(2)

Avoid allocating an array of strings for extracting query argument
values, instead append the current parameter value directly in the
buffer used to store the denormalized query.

This avoids not only unnecessary memory allocations, but also copying
data between temporary memory and the buffer.

pg_stat_monitor.c

@@ -208,8 +208,11 @@ static void pgsm_add_to_list(pgsmEntry *entry, char *query_text, int query_len);
 static pgsmEntry *pgsm_get_entry_for_query(uint64 queryid, PlanInfo *plan_info, const char *query_text, int query_len, bool create);
 static uint64 get_pgsm_query_id_hash(const char *norm_query, int len);
 
-/* transform parameters value from datum to string*/
-static char **get_params_text_list(const ParamListInfo paramlist);
+/*
+ * extract parameter value (Datum) from plist->params[idx], cast it to string then
+ * append the resulting string to the buffer.
+ */
+static void get_param_value(const ParamListInfo plist, int idx, StringInfoData *buffer);
 
 /* denormalize the query, replace placeholders with actual values */
 static StringInfoData get_denormalized_query(const ParamListInfo paramlist, const char *query_text);
@@ -706,8 +709,7 @@ pgsm_ExecutorEnd(QueryDesc *queryDesc)
 	/* Extract the plan information in case of SELECT statement */
 	if (queryDesc->operation == CMD_SELECT && pgsm_enable_query_plan)
 	{
-		int			rv;
-		MemoryContext oldctx;
+		int rv;
 
 		/*
 		 * Making sure it is a per query context so that there's no memory
@@ -4036,72 +4038,49 @@ get_query_id(JumbleState *jstate, Query *query)
 }
 #endif
 
-static char **
-get_params_text_list(const ParamListInfo paramlist)
+void
+get_param_value(const ParamListInfo plist, int idx, StringInfoData *buffer)
 {
-	StringInfoData  buf;
-	int             entry_num = paramlist->numParams;
-	int             i;
-	char          **params_text;
+	Oid  typoutput;
+	bool typisvarlena;
+	char *pstring;
+	ParamExternData *param;
 
-	initStringInfo(&buf);
-	params_text = (char **)palloc0(sizeof(char *) * entry_num);
+	Assert(idx < plist->numParams);
 
-	for(i = 0; i < entry_num; i++)
+	param = &plist->params[idx];
+
+	if (param->isnull || !OidIsValid(param->ptype))
 	{
-		ParamExternData *param = &paramlist->params[i];
-
-		if (param->isnull || !OidIsValid(param->ptype))
-		{
-			appendStringInfoString(&buf, "NULL");
-		}
-		else
-		{
-			Oid		typoutput;
-			bool	typisvarlena;
-			char	*pstring;
-
-			getTypeOutputInfo(param->ptype, &typoutput, &typisvarlena);
-			pstring = OidOutputFunctionCall(typoutput, param->value);
-			appendStringInfo(&buf, "%s",pstring);
-		}
-
-		/* assign memory space and add terminate symbol at the end of string*/
-		params_text[i] = (char *)palloc0(sizeof(char) * (buf.len + 1));
-		memcpy(params_text[i], buf.data, buf.len);
-		memset(params_text[i] + sizeof(char) * buf.len,'\0',sizeof(char));
-
-		/*clean the temp buffer*/
-		resetStringInfo(&buf);
+		appendStringInfoString(buffer, "NULL");
+		return;
 	}
 
-	return params_text;
+	getTypeOutputInfo(param->ptype, &typoutput, &typisvarlena);
+	pstring = OidOutputFunctionCall(typoutput, param->value);
+	appendStringInfo(buffer, "%s", pstring);
 }
 
 StringInfoData
 get_denormalized_query(const ParamListInfo paramlist, const char *query_text)
 {
 	int             current_param;
-	int             param_num;
-	int             i;
-	char          **param_text;
 	const char     *cursor_ori;
 	const char     *cursor_curr;
 	StringInfoData  result_buf;
 	ptrdiff_t       len;
 
-	param_text = get_params_text_list(paramlist);
-	param_num = paramlist->numParams;
 	current_param = 0;
 	cursor_ori = query_text;
 	cursor_curr = cursor_ori;
+
 	initStringInfo(&result_buf);
 
 	do
 	{
 		// advance cursor until detecting a placeholder '$' start.
 		while (*cursor_ori && *cursor_ori != '$')
-		++cursor_ori;
+			++cursor_ori;
 
 		// calculate length of query text before placeholder.
 		len = cursor_ori - cursor_curr;
@@ -4131,14 +4110,11 @@ get_denormalized_query(const ParamListInfo paramlist, const char *query_text)
 		cursor_curr = cursor_ori;
 
 		/* replace the placeholder with actual value */
-		appendStringInfoString(&result_buf, param_text[current_param++]);
+		get_param_value(paramlist, current_param, &result_buf);
+
+		++current_param;
 	} while (*cursor_ori != '\0');
 
-	/* free the query text array*/
-	for(i = 0; i < param_num; i++)
-		pfree(param_text[i]);
-
-	pfree(param_text);
 
 	return result_buf;
 }