Fix EXPLAIN ANALYZE bug noted by Wiebe Cazemier: although we were

tglsfdc · tglsfdc · commit 9fc24f2bf6e5 · 2005-10-21T16:43:33.000Z
properly advancing the CommandCounter between multiple sub-queries
generated by rules, we forgot to update the snapshot being used, so
that the successive sub-queries didn't actually see each others'
results.  This is still not *exactly* like the semantics of normal
execution of the same queries, in that we don't take new transaction
snapshots and hence don't see changes from concurrently committed
commands, but I think that's OK and probably even preferable for
EXPLAIN ANALYZE.
diff --git 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 1.138 2005/10/15 02:49:15 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.139 2005/10/21 16:43:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -196,6 +196,15 @@ ExplainOneQuery(Query *query, ExplainStmt *stmt, TupOutputState *tstate)
 	/* plan the query */
 	plan = planner(query, isCursor, cursorOptions, NULL);
 
+	/*
+	 * Update snapshot command ID to ensure this query sees results of any
+	 * previously executed queries.  (It's a bit cheesy to modify
+	 * ActiveSnapshot without making a copy, but for the limited ways in
+	 * which EXPLAIN can be invoked, I think it's OK, because the active
+	 * snapshot shouldn't be shared with anything else anyway.)
+	 */
+	ActiveSnapshot->curcid = GetCurrentCommandId();
+
 	/* Create a QueryDesc requesting no output */
 	queryDesc = CreateQueryDesc(query, plan,
 								ActiveSnapshot, InvalidSnapshot,
diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
@@ -10,7 +10,7 @@
  * Copyright (c) 2002-2005, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/prepare.c,v 1.41 2005/10/15 02:49:15 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/prepare.c,v 1.42 2005/10/21 16:43:33 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -605,6 +605,15 @@ ExplainExecuteQuery(ExplainStmt *stmt, TupOutputState *tstate)
 				query->into = execstmt->into;
 			}
 
+			/*
+			 * Update snapshot command ID to ensure this query sees results of
+			 * any previously executed queries.  (It's a bit cheesy to modify
+			 * ActiveSnapshot without making a copy, but for the limited ways
+			 * in which EXPLAIN can be invoked, I think it's OK, because the
+			 * active snapshot shouldn't be shared with anything else anyway.)
+			 */
+			ActiveSnapshot->curcid = GetCurrentCommandId();
+
 			/* Create a QueryDesc requesting no output */
 			qdesc = CreateQueryDesc(query, plan,
 									ActiveSnapshot, InvalidSnapshot,
