Create hooks to let a loadable plugin monitor (or even replace) the planner

and/or create plans for hypothetical situations; in particular, investigate
plans that would be generated using hypothetical indexes.  This is a
heavily-rewritten version of the hooks proposed by Gurjeet Singh for his
Index Advisor project.  In this formulation, the index advisor can be
entirely a loadable module instead of requiring a significant part to be
in the core backend, and plans can be generated for hypothetical indexes
without requiring the creation and rolling-back of system catalog entries.

The index advisor patch as-submitted is not compatible with these hooks,
but it needs significant work anyway due to other 8.2-to-8.3 planner
changes.  With these hooks in the core backend, development of the advisor
can proceed as a pgfoundry project.

1 files changed, 15 insertions, 3 deletions

diff --git a/src/include/commands/explain.h b/src/include/commands/explain.h
index 42879ce5a40..73bf41e49c1 100644
--- a/src/include/commands/explain.h
+++ b/src/include/commands/explain.h
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994-5, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/commands/explain.h,v 1.30 2007/03/13 00:33:43 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/commands/explain.h,v 1.31 2007/05/25 17:54:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -15,6 +15,18 @@
 
 #include "executor/executor.h"
 
+/* Hook for plugins to get control in ExplainOneQuery() */
+typedef void (*ExplainOneQuery_hook_type) (Query *query,
+										   ExplainStmt *stmt,
+										   const char *queryString,
+										   ParamListInfo params,
+										   TupOutputState *tstate);
+extern DLLIMPORT ExplainOneQuery_hook_type ExplainOneQuery_hook;
+
+/* Hook for plugins to get control in explain_get_index_name() */
+typedef const char * (*explain_get_index_name_hook_type) (Oid indexId);
+extern DLLIMPORT explain_get_index_name_hook_type explain_get_index_name_hook;
+
 
 extern void ExplainQuery(ExplainStmt *stmt, const char *queryString,
 						 ParamListInfo params, DestReceiver *dest);
@@ -26,7 +38,7 @@ extern void ExplainOneUtility(Node *utilityStmt, ExplainStmt *stmt,
 							  ParamListInfo params,
 							  TupOutputState *tstate);
 
-extern void ExplainOnePlan(QueryDesc *queryDesc, ExplainStmt *stmt,
-			   TupOutputState *tstate);
+extern void ExplainOnePlan(PlannedStmt *plannedstmt, ParamListInfo params,
+						   ExplainStmt *stmt, TupOutputState *tstate);
 
 #endif   /* EXPLAIN_H */