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.

1 files changed, 18 insertions, 49 deletions

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;
 }