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, 10 insertions, 23 deletions

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;
 }