pg_stat_statements vs. SELECT FOR UPDATE

[Andrew Gierth]

pg_stat_statements considers a plain select and a select for update to
be equivalent, which seems quite wrong to me as they will have very
different performance characteristics due to locking.

The only comment about it in the code is:

    /* we ignore rowMarks */

I propose that it should not ignore rowMarks, per the attached patch or
something similar.

(thanks to Vik Fearing for preliminary testing)

-- 
Andrew (irc:RhodiumToad)


diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index f177ebaa2c..080e7591c4 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -333,6 +333,7 @@ static void AppendJumble(pgssJumbleState *jstate,
 			 const unsigned char *item, Size size);
 static void JumbleQuery(pgssJumbleState *jstate, Query *query);
 static void JumbleRangeTable(pgssJumbleState *jstate, List *rtable);
+static void JumbleRowMarks(pgssJumbleState *jstate, List *rowMarks);
 static void JumbleExpr(pgssJumbleState *jstate, Node *node);
 static void RecordConstLocation(pgssJumbleState *jstate, int location);
 static char *generate_normalized_query(pgssJumbleState *jstate, const char *query,
@@ -2426,7 +2427,7 @@ JumbleQuery(pgssJumbleState *jstate, Query *query)
 	JumbleExpr(jstate, (Node *) query->sortClause);
 	JumbleExpr(jstate, query->limitOffset);
 	JumbleExpr(jstate, query->limitCount);
-	/* we ignore rowMarks */
+	JumbleRowMarks(jstate, query->rowMarks);
 	JumbleExpr(jstate, query->setOperations);
 }
 
@@ -2484,6 +2485,29 @@ JumbleRangeTable(pgssJumbleState *jstate, List *rtable)
 }
 
 /*
+ * Jumble a rowMarks list
+ */
+static void
+JumbleRowMarks(pgssJumbleState *jstate, List *rowMarks)
+{
+	ListCell   *lc;
+
+	foreach(lc, rowMarks)
+	{
+		RowMarkClause *rowmark = lfirst_node(RowMarkClause, lc);
+		/*
+		 * Ignore pushed down clauses as redundant.
+		 */
+		if (!rowmark->pushedDown)
+		{
+			APP_JUMB(rowmark->rti);
+			APP_JUMB(rowmark->strength);
+			APP_JUMB(rowmark->waitPolicy);
+		}
+	}
+}
+
+/*
  * Jumble an expression tree
  *
  * In general this function should handle all the same node types that