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.

6 files changed, 214 insertions, 98 deletions

diff --git a/src/backend/access/spgist/Makefile b/src/backend/access/spgist/Makefile
index 918da1fccaf..14948a531ee 100644
--- a/src/backend/access/spgist/Makefile
+++ b/src/backend/access/spgist/Makefile
@@ -12,7 +12,7 @@ subdir = src/backend/access/spgist
 top_builddir = ../../../..
 include $(top_builddir)/src/Makefile.global
 
-OBJS = spgutils.o spginsert.o spgscan.o spgvacuum.o \
+OBJS = spgutils.o spginsert.o spgscan.o spgvacuum.o spgvalidate.o \
 	spgdoinsert.o spgxlog.o \
 	spgtextproc.o spgquadtreeproc.o spgkdtreeproc.o
 
diff --git a/src/backend/access/spgist/spginsert.c b/src/backend/access/spgist/spginsert.c
index 0e6a180cc9e..44fd644e421 100644
--- a/src/backend/access/spgist/spginsert.c
+++ b/src/backend/access/spgist/spginsert.c
@@ -65,12 +65,9 @@ spgistBuildCallback(Relation index, HeapTuple htup, Datum *values,
 /*
  * Build an SP-GiST index.
  */
-Datum
-spgbuild(PG_FUNCTION_ARGS)
+IndexBuildResult *
+spgbuild(Relation heap, Relation index, IndexInfo *indexInfo)
 {
-	Relation	heap = (Relation) PG_GETARG_POINTER(0);
-	Relation	index = (Relation) PG_GETARG_POINTER(1);
-	IndexInfo  *indexInfo = (IndexInfo *) PG_GETARG_POINTER(2);
 	IndexBuildResult *result;
 	double		reltuples;
 	SpGistBuildState buildstate;
@@ -151,16 +148,15 @@ spgbuild(PG_FUNCTION_ARGS)
 	result = (IndexBuildResult *) palloc0(sizeof(IndexBuildResult));
 	result->heap_tuples = result->index_tuples = reltuples;
 
-	PG_RETURN_POINTER(result);
+	return result;
 }
 
 /*
  * Build an empty SPGiST index in the initialization fork
  */
-Datum
-spgbuildempty(PG_FUNCTION_ARGS)
+void
+spgbuildempty(Relation index)
 {
-	Relation	index = (Relation) PG_GETARG_POINTER(0);
 	Page		page;
 
 	/* Construct metapage. */
@@ -201,25 +197,16 @@ spgbuildempty(PG_FUNCTION_ARGS)
 	 * checkpoint may have moved the redo pointer past our xlog record.
 	 */
 	smgrimmedsync(index->rd_smgr, INIT_FORKNUM);
-
-	PG_RETURN_VOID();
 }
 
 /*
  * Insert one new tuple into an SPGiST index.
  */
-Datum
-spginsert(PG_FUNCTION_ARGS)
+bool
+spginsert(Relation index, Datum *values, bool *isnull,
+		  ItemPointer ht_ctid, Relation heapRel,
+		  IndexUniqueCheck checkUnique)
 {
-	Relation	index = (Relation) PG_GETARG_POINTER(0);
-	Datum	   *values = (Datum *) PG_GETARG_POINTER(1);
-	bool	   *isnull = (bool *) PG_GETARG_POINTER(2);
-	ItemPointer ht_ctid = (ItemPointer) PG_GETARG_POINTER(3);
-
-#ifdef NOT_USED
-	Relation	heapRel = (Relation) PG_GETARG_POINTER(4);
-	IndexUniqueCheck checkUnique = (IndexUniqueCheck) PG_GETARG_INT32(5);
-#endif
 	SpGistState spgstate;
 	MemoryContext oldCtx;
 	MemoryContext insertCtx;
@@ -251,5 +238,5 @@ spginsert(PG_FUNCTION_ARGS)
 	MemoryContextDelete(insertCtx);
 
 	/* return false since we've not done any unique check */
-	PG_RETURN_BOOL(false);
+	return false;
 }
diff --git a/src/backend/access/spgist/spgscan.c b/src/backend/access/spgist/spgscan.c
index 48e678c970e..620e7461998 100644
--- a/src/backend/access/spgist/spgscan.c
+++ b/src/backend/access/spgist/spgscan.c
@@ -173,13 +173,9 @@ spgPrepareScanKeys(IndexScanDesc scan)
 	}
 }
 
-Datum
-spgbeginscan(PG_FUNCTION_ARGS)
+IndexScanDesc
+spgbeginscan(Relation rel, int keysz, int orderbysz)
 {
-	Relation	rel = (Relation) PG_GETARG_POINTER(0);
-	int			keysz = PG_GETARG_INT32(1);
-
-	/* ScanKey			scankey = (ScanKey) PG_GETARG_POINTER(2); */
 	IndexScanDesc scan;
 	SpGistScanOpaque so;
 
@@ -202,15 +198,14 @@ spgbeginscan(PG_FUNCTION_ARGS)
 
 	scan->opaque = so;
 
-	PG_RETURN_POINTER(scan);
+	return scan;
 }
 
-Datum
-spgrescan(PG_FUNCTION_ARGS)
+void
+spgrescan(IndexScanDesc scan, ScanKey scankey, int nscankeys,
+		  ScanKey orderbys, int norderbys)
 {
-	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
 	SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;
-	ScanKey		scankey = (ScanKey) PG_GETARG_POINTER(1);
 
 	/* copy scankeys into local storage */
 	if (scankey && scan->numberOfKeys > 0)
@@ -224,33 +219,14 @@ spgrescan(PG_FUNCTION_ARGS)
 
 	/* set up starting stack entries */
 	resetSpGistScanOpaque(so);
-
-	PG_RETURN_VOID();
 }
 
-Datum
-spgendscan(PG_FUNCTION_ARGS)
+void
+spgendscan(IndexScanDesc scan)
 {
-	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
 	SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;
 
 	MemoryContextDelete(so->tempCxt);
-
-	PG_RETURN_VOID();
-}
-
-Datum
-spgmarkpos(PG_FUNCTION_ARGS)
-{
-	elog(ERROR, "SPGiST does not support mark/restore");
-	PG_RETURN_VOID();
-}
-
-Datum
-spgrestrpos(PG_FUNCTION_ARGS)
-{
-	elog(ERROR, "SPGiST does not support mark/restore");
-	PG_RETURN_VOID();
 }
 
 /*
@@ -571,11 +547,9 @@ storeBitmap(SpGistScanOpaque so, ItemPointer heapPtr,
 	so->ntids++;
 }
 
-Datum
-spggetbitmap(PG_FUNCTION_ARGS)
+int64
+spggetbitmap(IndexScanDesc scan, TIDBitmap *tbm)
 {
-	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
-	TIDBitmap  *tbm = (TIDBitmap *) PG_GETARG_POINTER(1);
 	SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;
 
 	/* Copy want_itup to *so so we don't need to pass it around separately */
@@ -586,7 +560,7 @@ spggetbitmap(PG_FUNCTION_ARGS)
 
 	spgWalk(scan->indexRelation, so, true, storeBitmap);
 
-	PG_RETURN_INT64(so->ntids);
+	return so->ntids;
 }
 
 /* storeRes subroutine for gettuple case */
@@ -610,11 +584,9 @@ storeGettuple(SpGistScanOpaque so, ItemPointer heapPtr,
 	so->nPtrs++;
 }
 
-Datum
-spggettuple(PG_FUNCTION_ARGS)
+bool
+spggettuple(IndexScanDesc scan, ScanDirection dir)
 {
-	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
-	ScanDirection dir = (ScanDirection) PG_GETARG_INT32(1);
 	SpGistScanOpaque so = (SpGistScanOpaque) scan->opaque;
 
 	if (dir != ForwardScanDirection)
@@ -632,7 +604,7 @@ spggettuple(PG_FUNCTION_ARGS)
 			scan->xs_recheck = so->recheck[so->iPtr];
 			scan->xs_itup = so->indexTups[so->iPtr];
 			so->iPtr++;
-			PG_RETURN_BOOL(true);
+			return true;
 		}
 
 		if (so->want_itup)
@@ -651,19 +623,16 @@ spggettuple(PG_FUNCTION_ARGS)
 			break;				/* must have completed scan */
 	}
 
-	PG_RETURN_BOOL(false);
+	return false;
 }
 
-Datum
-spgcanreturn(PG_FUNCTION_ARGS)
+bool
+spgcanreturn(Relation index, int attno)
 {
-	Relation	index = (Relation) PG_GETARG_POINTER(0);
-
-	/* int			i = PG_GETARG_INT32(1); */
 	SpGistCache *cache;
 
 	/* We can do it if the opclass config function says so */
 	cache = spgGetCache(index);
 
-	PG_RETURN_BOOL(cache->config.canReturnData);
+	return cache->config.canReturnData;
 }
diff --git a/src/backend/access/spgist/spgutils.c b/src/backend/access/spgist/spgutils.c
index 9ba077686a9..201203f91a3 100644
--- a/src/backend/access/spgist/spgutils.c
+++ b/src/backend/access/spgist/spgutils.c
@@ -15,7 +15,6 @@
 
 #include "postgres.h"
 
-#include "access/genam.h"
 #include "access/reloptions.h"
 #include "access/spgist_private.h"
 #include "access/transam.h"
@@ -23,9 +22,54 @@
 #include "storage/bufmgr.h"
 #include "storage/indexfsm.h"
 #include "storage/lmgr.h"
+#include "utils/index_selfuncs.h"
 #include "utils/lsyscache.h"
 
 
+/*
+ * SP-GiST handler function: return IndexAmRoutine with access method parameters
+ * and callbacks.
+ */
+Datum
+spghandler(PG_FUNCTION_ARGS)
+{
+	IndexAmRoutine *amroutine = makeNode(IndexAmRoutine);
+
+	amroutine->amstrategies = 0;
+	amroutine->amsupport = 5;
+	amroutine->amcanorder = false;
+	amroutine->amcanorderbyop = false;
+	amroutine->amcanbackward = false;
+	amroutine->amcanunique = false;
+	amroutine->amcanmulticol = false;
+	amroutine->amoptionalkey = true;
+	amroutine->amsearcharray = false;
+	amroutine->amsearchnulls = true;
+	amroutine->amstorage = false;
+	amroutine->amclusterable = false;
+	amroutine->ampredlocks = false;
+	amroutine->amkeytype = InvalidOid;
+
+	amroutine->ambuild = spgbuild;
+	amroutine->ambuildempty = spgbuildempty;
+	amroutine->aminsert = spginsert;
+	amroutine->ambulkdelete = spgbulkdelete;
+	amroutine->amvacuumcleanup = spgvacuumcleanup;
+	amroutine->amcanreturn = spgcanreturn;
+	amroutine->amcostestimate = spgcostestimate;
+	amroutine->amoptions = spgoptions;
+	amroutine->amvalidate = spgvalidate;
+	amroutine->ambeginscan = spgbeginscan;
+	amroutine->amrescan = spgrescan;
+	amroutine->amgettuple = spggettuple;
+	amroutine->amgetbitmap = spggetbitmap;
+	amroutine->amendscan = spgendscan;
+	amroutine->ammarkpos = NULL;
+	amroutine->amrestrpos = NULL;
+
+	PG_RETURN_POINTER(amroutine);
+}
+
 /* Fill in a SpGistTypeDesc struct with info about the specified data type */
 static void
 fillTypeDesc(SpGistTypeDesc *desc, Oid type)
@@ -489,18 +533,10 @@ SpGistInitMetapage(Page page)
 /*
  * reloptions processing for SPGiST
  */
-Datum
-spgoptions(PG_FUNCTION_ARGS)
+bytea *
+spgoptions(Datum reloptions, bool validate)
 {
-	Datum		reloptions = PG_GETARG_DATUM(0);
-	bool		validate = PG_GETARG_BOOL(1);
-	bytea	   *result;
-
-	result = default_reloptions(reloptions, validate, RELOPT_KIND_SPGIST);
-
-	if (result)
-		PG_RETURN_BYTEA_P(result);
-	PG_RETURN_NULL();
+	return default_reloptions(reloptions, validate, RELOPT_KIND_SPGIST);
 }
 
 /*
diff --git a/src/backend/access/spgist/spgvacuum.c b/src/backend/access/spgist/spgvacuum.c
index c2d4f0a68a6..15b867f24cb 100644
--- a/src/backend/access/spgist/spgvacuum.c
+++ b/src/backend/access/spgist/spgvacuum.c
@@ -881,13 +881,10 @@ spgvacuumscan(spgBulkDeleteState *bds)
  *
  * Result: a palloc'd struct containing statistical info for VACUUM displays.
  */
-Datum
-spgbulkdelete(PG_FUNCTION_ARGS)
+IndexBulkDeleteResult *
+spgbulkdelete(IndexVacuumInfo *info, IndexBulkDeleteResult *stats,
+			  IndexBulkDeleteCallback callback, void *callback_state)
 {
-	IndexVacuumInfo *info = (IndexVacuumInfo *) PG_GETARG_POINTER(0);
-	IndexBulkDeleteResult *stats = (IndexBulkDeleteResult *) PG_GETARG_POINTER(1);
-	IndexBulkDeleteCallback callback = (IndexBulkDeleteCallback) PG_GETARG_POINTER(2);
-	void	   *callback_state = (void *) PG_GETARG_POINTER(3);
 	spgBulkDeleteState bds;
 
 	/* allocate stats if first time through, else re-use existing struct */
@@ -900,7 +897,7 @@ spgbulkdelete(PG_FUNCTION_ARGS)
 
 	spgvacuumscan(&bds);
 
-	PG_RETURN_POINTER(stats);
+	return stats;
 }
 
 /* Dummy callback to delete no tuples during spgvacuumcleanup */
@@ -915,17 +912,15 @@ dummy_callback(ItemPointer itemptr, void *state)
  *
  * Result: a palloc'd struct containing statistical info for VACUUM displays.
  */
-Datum
-spgvacuumcleanup(PG_FUNCTION_ARGS)
+IndexBulkDeleteResult *
+spgvacuumcleanup(IndexVacuumInfo *info, IndexBulkDeleteResult *stats)
 {
-	IndexVacuumInfo *info = (IndexVacuumInfo *) PG_GETARG_POINTER(0);
-	IndexBulkDeleteResult *stats = (IndexBulkDeleteResult *) PG_GETARG_POINTER(1);
 	Relation	index = info->index;
 	spgBulkDeleteState bds;
 
 	/* No-op in ANALYZE ONLY mode */
 	if (info->analyze_only)
-		PG_RETURN_POINTER(stats);
+		return stats;
 
 	/*
 	 * We don't need to scan the index if there was a preceding bulkdelete
@@ -959,5 +954,5 @@ spgvacuumcleanup(PG_FUNCTION_ARGS)
 			stats->num_index_tuples = info->num_heap_tuples;
 	}
 
-	PG_RETURN_POINTER(stats);
+	return stats;
 }
diff --git a/src/backend/access/spgist/spgvalidate.c b/src/backend/access/spgist/spgvalidate.c
new file mode 100644
index 00000000000..c2d2d466d94
--- /dev/null
+++ b/src/backend/access/spgist/spgvalidate.c
@@ -0,0 +1,129 @@
+/*-------------------------------------------------------------------------
+ *
+ * spgvalidate.c
+ *	  Opclass validator for SP-GiST.
+ *
+ * Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *			src/backend/access/spgist/spgvalidate.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/htup_details.h"
+#include "access/spgist_private.h"
+#include "catalog/pg_amop.h"
+#include "catalog/pg_amproc.h"
+#include "catalog/pg_opclass.h"
+#include "utils/catcache.h"
+#include "utils/syscache.h"
+
+
+/*
+ * Validator for an SP-GiST opclass.
+ */
+bool
+spgvalidate(Oid opclassoid)
+{
+	HeapTuple	classtup;
+	Form_pg_opclass classform;
+	Oid			opfamilyoid;
+	Oid			opcintype;
+	int			numclassops;
+	int32		classfuncbits;
+	CatCList   *proclist,
+			   *oprlist;
+	int			i;
+
+	/* Fetch opclass information */
+	classtup = SearchSysCache1(CLAOID, ObjectIdGetDatum(opclassoid));
+	if (!HeapTupleIsValid(classtup))
+		elog(ERROR, "cache lookup failed for operator class %u", opclassoid);
+	classform = (Form_pg_opclass) GETSTRUCT(classtup);
+
+	opfamilyoid = classform->opcfamily;
+	opcintype = classform->opcintype;
+
+	ReleaseSysCache(classtup);
+
+	/* Fetch all operators and support functions of the opfamily */
+	oprlist = SearchSysCacheList1(AMOPSTRATEGY, ObjectIdGetDatum(opfamilyoid));
+	proclist = SearchSysCacheList1(AMPROCNUM, ObjectIdGetDatum(opfamilyoid));
+
+	/* We'll track the ops and functions belonging to the named opclass */
+	numclassops = 0;
+	classfuncbits = 0;
+
+	/* Check support functions */
+	for (i = 0; i < proclist->n_members; i++)
+	{
+		HeapTuple	proctup = &proclist->members[i]->tuple;
+		Form_pg_amproc procform = (Form_pg_amproc) GETSTRUCT(proctup);
+
+		/* Check that only allowed procedure numbers exist */
+		if (procform->amprocnum < 1 ||
+			procform->amprocnum > SPGISTNProc)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("spgist opfamily %u contains invalid support number %d for procedure %u",
+							opfamilyoid,
+							procform->amprocnum, procform->amproc)));
+
+		/* Remember functions that are specifically for the named opclass */
+		if (procform->amproclefttype == opcintype &&
+			procform->amprocrighttype == opcintype)
+			classfuncbits |= (1 << procform->amprocnum);
+	}
+
+	/* Check operators */
+	for (i = 0; i < oprlist->n_members; i++)
+	{
+		HeapTuple	oprtup = &oprlist->members[i]->tuple;
+		Form_pg_amop oprform = (Form_pg_amop) GETSTRUCT(oprtup);
+
+		/* TODO: Check that only allowed strategy numbers exist */
+		if (oprform->amopstrategy < 1)
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("spgist opfamily %u contains invalid strategy number %d for operator %u",
+							opfamilyoid,
+							oprform->amopstrategy, oprform->amopopr)));
+
+		/* spgist doesn't support ORDER BY operators */
+		if (oprform->amoppurpose != AMOP_SEARCH ||
+			OidIsValid(oprform->amopsortfamily))
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+					 errmsg("spgist opfamily %u contains invalid ORDER BY specification for operator %u",
+							opfamilyoid, oprform->amopopr)));
+
+		/* Count operators that are specifically for the named opclass */
+		if (oprform->amoplefttype == opcintype &&
+			oprform->amoprighttype == opcintype)
+			numclassops++;
+	}
+
+	/* Check that the named opclass is complete */
+	if (numclassops == 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+				 errmsg("spgist opclass %u is missing operator(s)",
+						opclassoid)));
+	for (i = 1; i <= SPGISTNProc; i++)
+	{
+		if ((classfuncbits & (1 << i)) != 0)
+			continue;			/* got it */
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
+		  errmsg("spgist opclass %u is missing required support function %d",
+				 opclassoid, i)));
+	}
+
+	ReleaseCatCacheList(proclist);
+	ReleaseCatCacheList(oprlist);
+
+	return true;
+}