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, 54 insertions, 22 deletions

diff --git a/src/backend/access/gist/gist.c b/src/backend/access/gist/gist.c
index 834d9d3335..996363c2de 100644
--- a/src/backend/access/gist/gist.c
+++ b/src/backend/access/gist/gist.c
@@ -14,17 +14,15 @@
  */
 #include "postgres.h"
 
-#include "access/genam.h"
 #include "access/gist_private.h"
-#include "access/xloginsert.h"
-#include "catalog/index.h"
+#include "access/gistscan.h"
 #include "catalog/pg_collation.h"
 #include "miscadmin.h"
-#include "storage/bufmgr.h"
-#include "storage/indexfsm.h"
+#include "utils/index_selfuncs.h"
 #include "utils/memutils.h"
 #include "utils/rel.h"
 
+
 /* non-export function prototypes */
 static void gistfixsplit(GISTInsertState *state, GISTSTATE *giststate);
 static bool gistinserttuple(GISTInsertState *state, GISTInsertStack *stack,
@@ -50,6 +48,50 @@ static void gistvacuumpage(Relation rel, Page page, Buffer buffer);
 
 
 /*
+ * GiST handler function: return IndexAmRoutine with access method parameters
+ * and callbacks.
+ */
+Datum
+gisthandler(PG_FUNCTION_ARGS)
+{
+	IndexAmRoutine *amroutine = makeNode(IndexAmRoutine);
+
+	amroutine->amstrategies = 0;
+	amroutine->amsupport = 9;
+	amroutine->amcanorder = false;
+	amroutine->amcanorderbyop = true;
+	amroutine->amcanbackward = false;
+	amroutine->amcanunique = false;
+	amroutine->amcanmulticol = true;
+	amroutine->amoptionalkey = true;
+	amroutine->amsearcharray = false;
+	amroutine->amsearchnulls = true;
+	amroutine->amstorage = true;
+	amroutine->amclusterable = true;
+	amroutine->ampredlocks = false;
+	amroutine->amkeytype = InvalidOid;
+
+	amroutine->ambuild = gistbuild;
+	amroutine->ambuildempty = gistbuildempty;
+	amroutine->aminsert = gistinsert;
+	amroutine->ambulkdelete = gistbulkdelete;
+	amroutine->amvacuumcleanup = gistvacuumcleanup;
+	amroutine->amcanreturn = gistcanreturn;
+	amroutine->amcostestimate = gistcostestimate;
+	amroutine->amoptions = gistoptions;
+	amroutine->amvalidate = gistvalidate;
+	amroutine->ambeginscan = gistbeginscan;
+	amroutine->amrescan = gistrescan;
+	amroutine->amgettuple = gistgettuple;
+	amroutine->amgetbitmap = gistgetbitmap;
+	amroutine->amendscan = gistendscan;
+	amroutine->ammarkpos = NULL;
+	amroutine->amrestrpos = NULL;
+
+	PG_RETURN_POINTER(amroutine);
+}
+
+/*
  * Create and return a temporary memory context for use by GiST. We
  * _always_ invoke user-provided methods in a temporary memory
  * context, so that memory leaks in those functions cannot cause
@@ -70,10 +112,9 @@ createTempGistContext(void)
 /*
  *	gistbuildempty() -- build an empty gist index in the initialization fork
  */
-Datum
-gistbuildempty(PG_FUNCTION_ARGS)
+void
+gistbuildempty(Relation index)
 {
-	Relation	index = (Relation) PG_GETARG_POINTER(0);
 	Buffer		buffer;
 
 	/* Initialize the root page */
@@ -89,8 +130,6 @@ gistbuildempty(PG_FUNCTION_ARGS)
 
 	/* Unlock and release the buffer */
 	UnlockReleaseBuffer(buffer);
-
-	PG_RETURN_VOID();
 }
 
 /*
@@ -99,18 +138,11 @@ gistbuildempty(PG_FUNCTION_ARGS)
  *	  This is the public interface routine for tuple insertion in GiSTs.
  *	  It doesn't do any work; just locks the relation and passes the buck.
  */
-Datum
-gistinsert(PG_FUNCTION_ARGS)
+bool
+gistinsert(Relation r, Datum *values, bool *isnull,
+		   ItemPointer ht_ctid, Relation heapRel,
+		   IndexUniqueCheck checkUnique)
 {
-	Relation	r = (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
 	IndexTuple	itup;
 	GISTSTATE  *giststate;
 	MemoryContext oldCxt;
@@ -136,7 +168,7 @@ gistinsert(PG_FUNCTION_ARGS)
 	MemoryContextSwitchTo(oldCxt);
 	freeGISTstate(giststate);
 
-	PG_RETURN_BOOL(false);
+	return false;
 }