From 1e67e0b5bda4ee4ee8e6db2d1fb7e1dc2f1fa90a Mon Sep 17 00:00:00 2001
From: Martin Sun <sunchengxi@highgo.com>
Date: Mon, 4 Jan 2021 21:02:35 +0800
Subject: [PATCH] PG-156: Adding a placeholder replacement function for
 prepared statement

When users set normalized_query to off and execute a prepared statement
user can see the actual value of parameters.

Reviewd By: Hamid Akhtar
---
 pg_stat_monitor.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)

diff --git a/pg_stat_monitor.c b/pg_stat_monitor.c
index 552162b..f91539a 100644
--- a/pg_stat_monitor.c
+++ b/pg_stat_monitor.c
@@ -245,6 +245,8 @@ pg_stat_monitor_version(PG_FUNCTION_ARGS)
 	PG_RETURN_TEXT_P(cstring_to_text(BUILD_VERSION));
 }
 
+static char **get_params_text_list(const ParamListInfo paramlist);
+static char *get_denormalized_query(const ParamListInfo paramlist, const char *query_text);
 
 /*
  * Post-parse-analysis hook: mark query with a queryId
@@ -397,6 +399,7 @@ pgss_ExecutorEnd(QueryDesc *queryDesc)
 	float   utime;
 	float   stime;
 	uint64	queryId = queryDesc->plannedstmt->queryId;
+	const char  *query_text;
 
 	if (queryId != UINT64CONST(0) && queryDesc->totaltime)
 	{
@@ -409,6 +412,15 @@ pgss_ExecutorEnd(QueryDesc *queryDesc)
 		utime = TIMEVAL_DIFF(rusage_start.ru_utime, rusage_end.ru_utime);
 		stime = TIMEVAL_DIFF(rusage_start.ru_stime, rusage_end.ru_stime);
 
+		/*
+		 * For a query with parameters if we want the actual query we denormalized it
+		 * by replacing all the placeholders with actual parameter values.
+		 */
+		if(!PGSM_NORMALIZED_QUERY && queryDesc->params)
+			query_text = get_denormalized_query(queryDesc->params, queryDesc->sourceText);
+		else
+			query_text = queryDesc->sourceText;
+
 		if (PGSM_ENABLED == 1)
 			pgss_store(queryId,
 						queryDesc->sourceText,
@@ -2596,3 +2608,93 @@ exit:
 	return buf_len;
 }
 
+/* transform parameters value from datum to string*/
+static char **
+get_params_text_list(const ParamListInfo paramlist)
+{
+	StringInfoData  buf;
+	int             entry_num = paramlist->numParams;
+	int             i;
+	char          **params_text;
+
+	initStringInfo(&buf);
+	params_text = (char **)palloc0(sizeof(char *) * entry_num);
+
+	for(i = 0; i < entry_num; i++)
+	{
+		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);
+	}
+	
+	return params_text;
+}
+
+/* denormalize the query, replace placeholder with actual value*/
+static char * 
+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;
+	StringInfoData  result_buf;
+
+	param_text = get_params_text_list(paramlist);
+	param_num = paramlist->numParams;
+	current_param = 0;
+	cursor_ori = query_text;
+	initStringInfo(&result_buf);
+
+	while(*cursor_ori != '\0')
+	{
+		if(*cursor_ori != '$')
+		{
+			/* copy the origin query string to result*/
+			appendStringInfoChar(&result_buf,*cursor_ori);
+			cursor_ori++;
+		}
+		else
+		{
+			/* skip the placeholder */
+			cursor_ori++;
+			while(*cursor_ori >= '0' && *cursor_ori <= '9')
+			{
+					cursor_ori++;
+			}
+			/* replace the placeholder with actual value */
+			appendStringInfo(&result_buf,"%s",param_text[current_param++]);
+		}
+	}
+
+	/* free the query text array*/
+	for(i = 0; i < param_num; i++)
+	{
+		pfree(param_text[i]);
+	}
+	pfree(param_text);
+
+	return result_buf.data;
+}
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