Restructure index access method API to hide most of it at the C level.

This patch reduces pg_am to just two columns, a name and a handler
function.  All the data formerly obtained from pg_am is now provided
in a C struct returned by the handler function.  This is similar to
the designs we've adopted for FDWs and tablesample methods.  There
are multiple advantages.  For one, the index AM's support functions
are now simple C functions, making them faster to call and much less
error-prone, since the C compiler can now check function signatures.
For another, this will make it far more practical to define index access
methods in installable extensions.

A disadvantage is that SQL-level code can no longer see attributes
of index AMs; in particular, some of the crosschecks in the opr_sanity
regression test are no longer possible from SQL.  We've addressed that
by adding a facility for the index AM to perform such checks instead.
(Much more could be done in that line, but for now we're content if the
amvalidate functions more or less replace what opr_sanity used to do.)
We might also want to expose some sort of reporting functionality, but
this patch doesn't do that.

Alexander Korotkov, reviewed by Petr Jelínek, and rather heavily
editorialized on by me.

4 files changed, 75 insertions, 29 deletions

diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.h
index b35d20626b7..477fde1f81d 100644
--- a/src/include/utils/builtins.h
+++ b/src/include/utils/builtins.h
@@ -566,6 +566,8 @@ extern Datum language_handler_in(PG_FUNCTION_ARGS);
 extern Datum language_handler_out(PG_FUNCTION_ARGS);
 extern Datum fdw_handler_in(PG_FUNCTION_ARGS);
 extern Datum fdw_handler_out(PG_FUNCTION_ARGS);
+extern Datum index_am_handler_in(PG_FUNCTION_ARGS);
+extern Datum index_am_handler_out(PG_FUNCTION_ARGS);
 extern Datum tsm_handler_in(PG_FUNCTION_ARGS);
 extern Datum tsm_handler_out(PG_FUNCTION_ARGS);
 extern Datum internal_in(PG_FUNCTION_ARGS);
diff --git a/src/include/utils/index_selfuncs.h b/src/include/utils/index_selfuncs.h
new file mode 100644
index 00000000000..a03e12f518f
--- /dev/null
+++ b/src/include/utils/index_selfuncs.h
@@ -0,0 +1,68 @@
+/*-------------------------------------------------------------------------
+ *
+ * index_selfuncs.h
+ *	  Index cost estimation functions for standard index access methods.
+ *
+ *
+ * Note: this is split out of selfuncs.h mainly to avoid importing all of the
+ * planner's data structures into the non-planner parts of the index AMs.
+ * If you make it depend on anything besides access/amapi.h, that's likely
+ * a mistake.
+ *
+ * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/utils/index_selfuncs.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef INDEX_SELFUNCS_H
+#define INDEX_SELFUNCS_H
+
+#include "access/amapi.h"
+
+/* Functions in selfuncs.c */
+extern void brincostestimate(struct PlannerInfo *root,
+				 struct IndexPath *path,
+				 double loop_count,
+				 Cost *indexStartupCost,
+				 Cost *indexTotalCost,
+				 Selectivity *indexSelectivity,
+				 double *indexCorrelation);
+extern void btcostestimate(struct PlannerInfo *root,
+			   struct IndexPath *path,
+			   double loop_count,
+			   Cost *indexStartupCost,
+			   Cost *indexTotalCost,
+			   Selectivity *indexSelectivity,
+			   double *indexCorrelation);
+extern void hashcostestimate(struct PlannerInfo *root,
+				 struct IndexPath *path,
+				 double loop_count,
+				 Cost *indexStartupCost,
+				 Cost *indexTotalCost,
+				 Selectivity *indexSelectivity,
+				 double *indexCorrelation);
+extern void gistcostestimate(struct PlannerInfo *root,
+				 struct IndexPath *path,
+				 double loop_count,
+				 Cost *indexStartupCost,
+				 Cost *indexTotalCost,
+				 Selectivity *indexSelectivity,
+				 double *indexCorrelation);
+extern void spgcostestimate(struct PlannerInfo *root,
+				struct IndexPath *path,
+				double loop_count,
+				Cost *indexStartupCost,
+				Cost *indexTotalCost,
+				Selectivity *indexSelectivity,
+				double *indexCorrelation);
+extern void gincostestimate(struct PlannerInfo *root,
+				struct IndexPath *path,
+				double loop_count,
+				Cost *indexStartupCost,
+				Cost *indexTotalCost,
+				Selectivity *indexSelectivity,
+				double *indexCorrelation);
+
+#endif   /* INDEX_SELFUNCS_H */
diff --git a/src/include/utils/rel.h b/src/include/utils/rel.h
index ff5672d2654..f2bebf2c3dd 100644
--- a/src/include/utils/rel.h
+++ b/src/include/utils/rel.h
@@ -15,7 +15,6 @@
 #define REL_H
 
 #include "access/tupdesc.h"
-#include "catalog/pg_am.h"
 #include "catalog/pg_class.h"
 #include "catalog/pg_index.h"
 #include "fmgr.h"
@@ -47,23 +46,6 @@ typedef LockInfoData *LockInfo;
 
 
 /*
- * Cached lookup information for the frequently used index access method
- * functions, defined by the pg_am row associated with an index relation.
- */
-typedef struct RelationAmInfo
-{
-	FmgrInfo	aminsert;
-	FmgrInfo	ambeginscan;
-	FmgrInfo	amgettuple;
-	FmgrInfo	amgetbitmap;
-	FmgrInfo	amrescan;
-	FmgrInfo	amendscan;
-	FmgrInfo	ammarkpos;
-	FmgrInfo	amrestrpos;
-	FmgrInfo	amcanreturn;
-} RelationAmInfo;
-
-/*
  * Here are the contents of a relation cache entry.
  */
 
@@ -128,7 +110,6 @@ typedef struct RelationData
 	Form_pg_index rd_index;		/* pg_index tuple describing this index */
 	/* use "struct" here to avoid needing to include htup.h: */
 	struct HeapTupleData *rd_indextuple;		/* all of pg_index tuple */
-	Form_pg_am	rd_am;			/* pg_am tuple for index's AM */
 
 	/*
 	 * index access support info (used only for an index relation)
@@ -145,8 +126,10 @@ typedef struct RelationData
 	 * rd_indexcxt.  A relcache reset will include freeing that chunk and
 	 * setting rd_amcache = NULL.
 	 */
+	Oid			rd_amhandler;	/* OID of index AM's handler function */
 	MemoryContext rd_indexcxt;	/* private memory cxt for this stuff */
-	RelationAmInfo *rd_aminfo;	/* lookup info for funcs found in pg_am */
+	/* use "struct" here to avoid needing to include amapi.h: */
+	struct IndexAmRoutine *rd_amroutine;		/* index AM's API struct */
 	Oid		   *rd_opfamily;	/* OIDs of op families for each index col */
 	Oid		   *rd_opcintype;	/* OIDs of opclass declared input data types */
 	RegProcedure *rd_support;	/* OIDs of support procedures */
diff --git a/src/include/utils/selfuncs.h b/src/include/utils/selfuncs.h
index 38fe731f81e..06fbca719b5 100644
--- a/src/include/utils/selfuncs.h
+++ b/src/include/utils/selfuncs.h
@@ -1,8 +1,8 @@
 /*-------------------------------------------------------------------------
  *
  * selfuncs.h
- *	  Selectivity functions and index cost estimation functions for
- *	  standard operators and index access methods.
+ *	  Selectivity functions for standard operators, and assorted
+ *	  infrastructure for selectivity and cost estimation.
  *
  *
  * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
@@ -191,13 +191,6 @@ extern double estimate_num_groups(PlannerInfo *root, List *groupExprs,
 extern Selectivity estimate_hash_bucketsize(PlannerInfo *root, Node *hashkey,
 						 double nbuckets);
 
-extern Datum brincostestimate(PG_FUNCTION_ARGS);
-extern Datum btcostestimate(PG_FUNCTION_ARGS);
-extern Datum hashcostestimate(PG_FUNCTION_ARGS);
-extern Datum gistcostestimate(PG_FUNCTION_ARGS);
-extern Datum spgcostestimate(PG_FUNCTION_ARGS);
-extern Datum gincostestimate(PG_FUNCTION_ARGS);
-
 /* Functions in array_selfuncs.c */
 
 extern Selectivity scalararraysel_containment(PlannerInfo *root,