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.

src/backend/access/index/Makefile

@@ -12,6 +12,6 @@ subdir = src/backend/access/index
 top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
-OBJS = genam.o indexam.o
+OBJS = amapi.o genam.o indexam.o
 
 include $(top_srcdir)/src/backend/common.mk

src/backend/access/index/amapi.c

@@ -0,0 +1,114 @@
+/*-------------------------------------------------------------------------
+ *
+ * amapi.c
+ *	  Support routines for API for Postgres index access methods.
+ *
+ * Copyright (c) 2015-2016, PostgreSQL Global Development Group
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/index/amapi.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/amapi.h"
+#include "access/htup_details.h"
+#include "catalog/pg_am.h"
+#include "catalog/pg_opclass.h"
+#include "utils/syscache.h"
+
+
+/*
+ * GetIndexAmRoutine - call the specified access method handler routine to get
+ * its IndexAmRoutine struct, which will be palloc'd in the caller's context.
+ *
+ * Note that if the amhandler function is built-in, this will not involve
+ * any catalog access.  It's therefore safe to use this while bootstrapping
+ * indexes for the system catalogs.  relcache.c relies on that.
+ */
+IndexAmRoutine *
+GetIndexAmRoutine(Oid amhandler)
+{
+	Datum		datum;
+	IndexAmRoutine *routine;
+
+	datum = OidFunctionCall0(amhandler);
+	routine = (IndexAmRoutine *) DatumGetPointer(datum);
+
+	if (routine == NULL || !IsA(routine, IndexAmRoutine))
+		elog(ERROR, "index access method handler function %u did not return an IndexAmRoutine struct",
+			 amhandler);
+
+	return routine;
+}
+
+/*
+ * GetIndexAmRoutineByAmId - look up the handler of the index access method
+ * with the given OID, and get its IndexAmRoutine struct.
+ */
+IndexAmRoutine *
+GetIndexAmRoutineByAmId(Oid amoid)
+{
+	HeapTuple	tuple;
+	Form_pg_am	amform;
+	regproc		amhandler;
+
+	/* Get handler function OID for the access method */
+	tuple = SearchSysCache1(AMOID, ObjectIdGetDatum(amoid));
+	if (!HeapTupleIsValid(tuple))
+		elog(ERROR, "cache lookup failed for access method %u",
+			 amoid);
+	amform = (Form_pg_am) GETSTRUCT(tuple);
+
+	amhandler = amform->amhandler;
+
+	/* Complain if handler OID is invalid */
+	if (!RegProcedureIsValid(amhandler))
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("index access method \"%s\" does not have a handler",
+						NameStr(amform->amname))));
+
+	ReleaseSysCache(tuple);
+
+	/* And finally, call the handler function to get the API struct. */
+	return GetIndexAmRoutine(amhandler);
+}
+
+
+/*
+ * Ask appropriate access method to validate the specified opclass.
+ */
+Datum
+amvalidate(PG_FUNCTION_ARGS)
+{
+	Oid			opclassoid = PG_GETARG_OID(0);
+	bool		result;
+	HeapTuple	classtup;
+	Form_pg_opclass classform;
+	Oid			amoid;
+	IndexAmRoutine *amroutine;
+
+	classtup = SearchSysCache1(CLAOID, ObjectIdGetDatum(opclassoid));
+	if (!HeapTupleIsValid(classtup))
+		elog(ERROR, "cache lookup failed for operator class %u", opclassoid);
+	classform = (Form_pg_opclass) GETSTRUCT(classtup);
+
+	amoid = classform->opcmethod;
+
+	ReleaseSysCache(classtup);
+
+	amroutine = GetIndexAmRoutineByAmId(amoid);
+
+	if (amroutine->amvalidate == NULL)
+		elog(ERROR, "function amvalidate is not defined for index access method %u",
+			 amoid);
+
+	result = amroutine->amvalidate(opclassoid);
+
+	pfree(amroutine);
+
+	PG_RETURN_BOOL(result);
+}

src/backend/access/index/indexam.c

@@ -65,12 +65,12 @@
 
 #include "postgres.h"
 
+#include "access/amapi.h"
 #include "access/relscan.h"
 #include "access/transam.h"
 #include "access/xlog.h"
-
-#include "catalog/index.h"
 #include "catalog/catalog.h"
+#include "catalog/index.h"
 #include "pgstat.h"
 #include "storage/bufmgr.h"
 #include "storage/lmgr.h"
@@ -94,7 +94,7 @@
 #define RELATION_CHECKS \
 ( \
 	AssertMacro(RelationIsValid(indexRelation)), \
-	AssertMacro(PointerIsValid(indexRelation->rd_am)), \
+	AssertMacro(PointerIsValid(indexRelation->rd_amroutine)), \
 	AssertMacro(!ReindexIsProcessingIndex(RelationGetRelid(indexRelation))) \
 )
 
@@ -102,38 +102,21 @@
 ( \
 	AssertMacro(IndexScanIsValid(scan)), \
 	AssertMacro(RelationIsValid(scan->indexRelation)), \
-	AssertMacro(PointerIsValid(scan->indexRelation->rd_am)) \
+	AssertMacro(PointerIsValid(scan->indexRelation->rd_amroutine)) \
 )
 
-#define GET_REL_PROCEDURE(pname) \
+#define CHECK_REL_PROCEDURE(pname) \
 do { \
-	procedure = &indexRelation->rd_aminfo->pname; \
-	if (!OidIsValid(procedure->fn_oid)) \
-	{ \
-		RegProcedure	procOid = indexRelation->rd_am->pname; \
-		if (!RegProcedureIsValid(procOid)) \
-			elog(ERROR, "invalid %s regproc", CppAsString(pname)); \
-		fmgr_info_cxt(procOid, procedure, indexRelation->rd_indexcxt); \
-	} \
+	if (indexRelation->rd_amroutine->pname == NULL) \
+		elog(ERROR, "function %s is not defined for index %s", \
+			 CppAsString(pname), RelationGetRelationName(indexRelation)); \
 } while(0)
 
-#define GET_UNCACHED_REL_PROCEDURE(pname) \
+#define CHECK_SCAN_PROCEDURE(pname) \
 do { \
-	if (!RegProcedureIsValid(indexRelation->rd_am->pname)) \
-		elog(ERROR, "invalid %s regproc", CppAsString(pname)); \
-	fmgr_info(indexRelation->rd_am->pname, &procedure); \
-} while(0)
-
-#define GET_SCAN_PROCEDURE(pname) \
-do { \
-	procedure = &scan->indexRelation->rd_aminfo->pname; \
-	if (!OidIsValid(procedure->fn_oid)) \
-	{ \
-		RegProcedure	procOid = scan->indexRelation->rd_am->pname; \
-		if (!RegProcedureIsValid(procOid)) \
-			elog(ERROR, "invalid %s regproc", CppAsString(pname)); \
-		fmgr_info_cxt(procOid, procedure, scan->indexRelation->rd_indexcxt); \
-	} \
+	if (scan->indexRelation->rd_amroutine->pname == NULL) \
+		elog(ERROR, "function %s is not defined for index %s", \
+			 CppAsString(pname), RelationGetRelationName(scan->indexRelation)); \
 } while(0)
 
 static IndexScanDesc index_beginscan_internal(Relation indexRelation,
@@ -210,26 +193,17 @@ index_insert(Relation indexRelation,
 			 Relation heapRelation,
 			 IndexUniqueCheck checkUnique)
 {
-	FmgrInfo   *procedure;
-
 	RELATION_CHECKS;
-	GET_REL_PROCEDURE(aminsert);
+	CHECK_REL_PROCEDURE(aminsert);
 
-	if (!(indexRelation->rd_am->ampredlocks))
+	if (!(indexRelation->rd_amroutine->ampredlocks))
 		CheckForSerializableConflictIn(indexRelation,
 									   (HeapTuple) NULL,
 									   InvalidBuffer);
 
-	/*
-	 * have the am's insert proc do all the work.
-	 */
-	return DatumGetBool(FunctionCall6(procedure,
-									  PointerGetDatum(indexRelation),
-									  PointerGetDatum(values),
-									  PointerGetDatum(isnull),
-									  PointerGetDatum(heap_t_ctid),
-									  PointerGetDatum(heapRelation),
-									  Int32GetDatum((int32) checkUnique)));
+	return indexRelation->rd_amroutine->aminsert(indexRelation, values, isnull,
+												 heap_t_ctid, heapRelation,
+												 checkUnique);
 }
 
 /*
@@ -288,13 +262,10 @@ static IndexScanDesc
 index_beginscan_internal(Relation indexRelation,
 						 int nkeys, int norderbys, Snapshot snapshot)
 {
-	IndexScanDesc scan;
-	FmgrInfo   *procedure;
-
 	RELATION_CHECKS;
-	GET_REL_PROCEDURE(ambeginscan);
+	CHECK_REL_PROCEDURE(ambeginscan);
 
-	if (!(indexRelation->rd_am->ampredlocks))
+	if (!(indexRelation->rd_amroutine->ampredlocks))
 		PredicateLockRelation(indexRelation, snapshot);
 
 	/*
@@ -305,13 +276,8 @@ index_beginscan_internal(Relation indexRelation,
 	/*
 	 * Tell the AM to open a scan.
 	 */
-	scan = (IndexScanDesc)
-		DatumGetPointer(FunctionCall3(procedure,
-									  PointerGetDatum(indexRelation),
-									  Int32GetDatum(nkeys),
-									  Int32GetDatum(norderbys)));
-
-	return scan;
+	return indexRelation->rd_amroutine->ambeginscan(indexRelation, nkeys,
+													norderbys);
 }
 
 /* ----------------
@@ -331,10 +297,8 @@ index_rescan(IndexScanDesc scan,
 			 ScanKey keys, int nkeys,
 			 ScanKey orderbys, int norderbys)
 {
-	FmgrInfo   *procedure;
-
 	SCAN_CHECKS;
-	GET_SCAN_PROCEDURE(amrescan);
+	CHECK_SCAN_PROCEDURE(amrescan);
 
 	Assert(nkeys == scan->numberOfKeys);
 	Assert(norderbys == scan->numberOfOrderBys);
@@ -350,12 +314,8 @@ index_rescan(IndexScanDesc scan,
 
 	scan->kill_prior_tuple = false;		/* for safety */
 
-	FunctionCall5(procedure,
-				  PointerGetDatum(scan),
-				  PointerGetDatum(keys),
-				  Int32GetDatum(nkeys),
-				  PointerGetDatum(orderbys),
-				  Int32GetDatum(norderbys));
+	scan->indexRelation->rd_amroutine->amrescan(scan, keys, nkeys,
+												orderbys, norderbys);
 }
 
 /* ----------------
@@ -365,10 +325,8 @@ index_rescan(IndexScanDesc scan,
 void
 index_endscan(IndexScanDesc scan)
 {
-	FmgrInfo   *procedure;
-
 	SCAN_CHECKS;
-	GET_SCAN_PROCEDURE(amendscan);
+	CHECK_SCAN_PROCEDURE(amendscan);
 
 	/* Release any held pin on a heap page */
 	if (BufferIsValid(scan->xs_cbuf))
@@ -378,7 +336,7 @@ index_endscan(IndexScanDesc scan)
 	}
 
 	/* End the AM's scan */
-	FunctionCall1(procedure, PointerGetDatum(scan));
+	scan->indexRelation->rd_amroutine->amendscan(scan);
 
 	/* Release index refcount acquired by index_beginscan */
 	RelationDecrementReferenceCount(scan->indexRelation);
@@ -394,12 +352,10 @@ index_endscan(IndexScanDesc scan)
 void
 index_markpos(IndexScanDesc scan)
 {
-	FmgrInfo   *procedure;
-
 	SCAN_CHECKS;
-	GET_SCAN_PROCEDURE(ammarkpos);
+	CHECK_SCAN_PROCEDURE(ammarkpos);
 
-	FunctionCall1(procedure, PointerGetDatum(scan));
+	scan->indexRelation->rd_amroutine->ammarkpos(scan);
 }
 
 /* ----------------
@@ -421,18 +377,16 @@ index_markpos(IndexScanDesc scan)
 void
 index_restrpos(IndexScanDesc scan)
 {
-	FmgrInfo   *procedure;
-
 	Assert(IsMVCCSnapshot(scan->xs_snapshot));
 
 	SCAN_CHECKS;
-	GET_SCAN_PROCEDURE(amrestrpos);
+	CHECK_SCAN_PROCEDURE(amrestrpos);
 
 	scan->xs_continue_hot = false;
 
 	scan->kill_prior_tuple = false;		/* for safety */
 
-	FunctionCall1(procedure, PointerGetDatum(scan));
+	scan->indexRelation->rd_amroutine->amrestrpos(scan);
 }
 
 /* ----------------
@@ -445,11 +399,10 @@ index_restrpos(IndexScanDesc scan)
 ItemPointer
 index_getnext_tid(IndexScanDesc scan, ScanDirection direction)
 {
-	FmgrInfo   *procedure;
 	bool		found;
 
 	SCAN_CHECKS;
-	GET_SCAN_PROCEDURE(amgettuple);
+	CHECK_SCAN_PROCEDURE(amgettuple);
 
 	Assert(TransactionIdIsValid(RecentGlobalXmin));
 
@@ -459,9 +412,7 @@ index_getnext_tid(IndexScanDesc scan, ScanDirection direction)
 	 * scan->xs_recheck and possibly scan->xs_itup, though we pay no attention
 	 * to those fields here.
 	 */
-	found = DatumGetBool(FunctionCall2(procedure,
-									   PointerGetDatum(scan),
-									   Int32GetDatum(direction)));
+	found = scan->indexRelation->rd_amroutine->amgettuple(scan, direction);
 
 	/* Reset kill flag immediately for safety */
 	scan->kill_prior_tuple = false;
@@ -635,12 +586,10 @@ index_getnext(IndexScanDesc scan, ScanDirection direction)
 int64
 index_getbitmap(IndexScanDesc scan, TIDBitmap *bitmap)
 {
-	FmgrInfo   *procedure;
 	int64		ntids;
-	Datum		d;
 
 	SCAN_CHECKS;
-	GET_SCAN_PROCEDURE(amgetbitmap);
+	CHECK_SCAN_PROCEDURE(amgetbitmap);
 
 	/* just make sure this is false... */
 	scan->kill_prior_tuple = false;
@@ -648,16 +597,7 @@ index_getbitmap(IndexScanDesc scan, TIDBitmap *bitmap)
 	/*
 	 * have the am's getbitmap proc do all the work.
 	 */
-	d = FunctionCall2(procedure,
-					  PointerGetDatum(scan),
-					  PointerGetDatum(bitmap));
-
-	ntids = DatumGetInt64(d);
-
-	/* If int8 is pass-by-ref, must free the result to avoid memory leak */
-#ifndef USE_FLOAT8_BYVAL
-	pfree(DatumGetPointer(d));
-#endif
+	ntids = scan->indexRelation->rd_amroutine->amgetbitmap(scan, bitmap);
 
 	pgstat_count_index_tuples(scan->indexRelation, ntids);
 
@@ -680,20 +620,12 @@ index_bulk_delete(IndexVacuumInfo *info,
 				  void *callback_state)
 {
 	Relation	indexRelation = info->index;
-	FmgrInfo	procedure;
-	IndexBulkDeleteResult *result;
 
 	RELATION_CHECKS;
-	GET_UNCACHED_REL_PROCEDURE(ambulkdelete);
+	CHECK_REL_PROCEDURE(ambulkdelete);
 
-	result = (IndexBulkDeleteResult *)
-		DatumGetPointer(FunctionCall4(&procedure,
-									  PointerGetDatum(info),
-									  PointerGetDatum(stats),
-									  PointerGetDatum((Pointer) callback),
-									  PointerGetDatum(callback_state)));
-
-	return result;
+	return indexRelation->rd_amroutine->ambulkdelete(info, stats,
+												   callback, callback_state);
 }
 
 /* ----------------
@@ -707,18 +639,11 @@ index_vacuum_cleanup(IndexVacuumInfo *info,
 					 IndexBulkDeleteResult *stats)
 {
 	Relation	indexRelation = info->index;
-	FmgrInfo	procedure;
-	IndexBulkDeleteResult *result;
 
 	RELATION_CHECKS;
-	GET_UNCACHED_REL_PROCEDURE(amvacuumcleanup);
+	CHECK_REL_PROCEDURE(amvacuumcleanup);
 
-	result = (IndexBulkDeleteResult *)
-		DatumGetPointer(FunctionCall2(&procedure,
-									  PointerGetDatum(info),
-									  PointerGetDatum(stats)));
-
-	return result;
+	return indexRelation->rd_amroutine->amvacuumcleanup(info, stats);
 }
 
 /* ----------------
@@ -731,19 +656,13 @@ index_vacuum_cleanup(IndexVacuumInfo *info,
 bool
 index_can_return(Relation indexRelation, int attno)
 {
-	FmgrInfo   *procedure;
-
 	RELATION_CHECKS;
 
 	/* amcanreturn is optional; assume FALSE if not provided by AM */
-	if (!RegProcedureIsValid(indexRelation->rd_am->amcanreturn))
+	if (indexRelation->rd_amroutine->amcanreturn == NULL)
 		return false;
 
-	GET_REL_PROCEDURE(amcanreturn);
-
-	return DatumGetBool(FunctionCall2(procedure,
-									  PointerGetDatum(indexRelation),
-									  Int32GetDatum(attno)));
+	return indexRelation->rd_amroutine->amcanreturn(indexRelation, attno);
 }
 
 /* ----------------
@@ -781,7 +700,7 @@ index_getprocid(Relation irel,
 	int			nproc;
 	int			procindex;
 
-	nproc = irel->rd_am->amsupport;
+	nproc = irel->rd_amroutine->amsupport;
 
 	Assert(procnum > 0 && procnum <= (uint16) nproc);
 
@@ -815,7 +734,7 @@ index_getprocinfo(Relation irel,
 	int			nproc;
 	int			procindex;
 
-	nproc = irel->rd_am->amsupport;
+	nproc = irel->rd_amroutine->amsupport;
 
 	Assert(procnum > 0 && procnum <= (uint16) nproc);