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.

2 files changed, 21 insertions, 17 deletions

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 4e17fac6c13..8fb483aaebd 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -75,6 +75,7 @@
 #endif
 #include <math.h>
 
+#include "access/amapi.h"
 #include "access/htup_details.h"
 #include "access/tsmapi.h"
 #include "executor/executor.h"
@@ -364,6 +365,7 @@ cost_index(IndexPath *path, PlannerInfo *root, double loop_count)
 	IndexOptInfo *index = path->indexinfo;
 	RelOptInfo *baserel = index->rel;
 	bool		indexonly = (path->path.pathtype == T_IndexOnlyScan);
+	amcostestimate_function amcostestimate;
 	List	   *qpquals;
 	Cost		startup_cost = 0;
 	Cost		run_cost = 0;
@@ -419,14 +421,10 @@ cost_index(IndexPath *path, PlannerInfo *root, double loop_count)
 	 * the fraction of main-table tuples we will have to retrieve) and its
 	 * correlation to the main-table tuple order.
 	 */
-	OidFunctionCall7(index->amcostestimate,
-					 PointerGetDatum(root),
-					 PointerGetDatum(path),
-					 Float8GetDatum(loop_count),
-					 PointerGetDatum(&indexStartupCost),
-					 PointerGetDatum(&indexTotalCost),
-					 PointerGetDatum(&indexSelectivity),
-					 PointerGetDatum(&indexCorrelation));
+	amcostestimate = index->amcostestimate;		/* cast to proper type */
+	amcostestimate(root, path, loop_count,
+				   &indexStartupCost, &indexTotalCost,
+				   &indexSelectivity, &indexCorrelation);
 
 	/*
 	 * Save amcostestimate's results for possible use in bitmap scan planning.
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index d5528e03818..0ea9fcf7c20 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -27,6 +27,7 @@
 #include "catalog/catalog.h"
 #include "catalog/dependency.h"
 #include "catalog/heap.h"
+#include "catalog/pg_am.h"
 #include "foreign/fdwapi.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
@@ -163,6 +164,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 			Oid			indexoid = lfirst_oid(l);
 			Relation	indexRelation;
 			Form_pg_index index;
+			IndexAmRoutine *amroutine;
 			IndexOptInfo *info;
 			int			ncolumns;
 			int			i;
@@ -223,13 +225,17 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 			}
 
 			info->relam = indexRelation->rd_rel->relam;
-			info->amcostestimate = indexRelation->rd_am->amcostestimate;
-			info->amcanorderbyop = indexRelation->rd_am->amcanorderbyop;
-			info->amoptionalkey = indexRelation->rd_am->amoptionalkey;
-			info->amsearcharray = indexRelation->rd_am->amsearcharray;
-			info->amsearchnulls = indexRelation->rd_am->amsearchnulls;
-			info->amhasgettuple = OidIsValid(indexRelation->rd_am->amgettuple);
-			info->amhasgetbitmap = OidIsValid(indexRelation->rd_am->amgetbitmap);
+
+			/* We copy just the fields we need, not all of rd_amroutine */
+			amroutine = indexRelation->rd_amroutine;
+			info->amcanorderbyop = amroutine->amcanorderbyop;
+			info->amoptionalkey = amroutine->amoptionalkey;
+			info->amsearcharray = amroutine->amsearcharray;
+			info->amsearchnulls = amroutine->amsearchnulls;
+			info->amhasgettuple = (amroutine->amgettuple != NULL);
+			info->amhasgetbitmap = (amroutine->amgetbitmap != NULL);
+			info->amcostestimate = amroutine->amcostestimate;
+			Assert(info->amcostestimate != NULL);
 
 			/*
 			 * Fetch the ordering information for the index, if any.
@@ -240,7 +246,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 				 * If it's a btree index, we can use its opfamily OIDs
 				 * directly as the sort ordering opfamily OIDs.
 				 */
-				Assert(indexRelation->rd_am->amcanorder);
+				Assert(amroutine->amcanorder);
 
 				info->sortopfamily = info->opfamily;
 				info->reverse_sort = (bool *) palloc(sizeof(bool) * ncolumns);
@@ -254,7 +260,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 					info->nulls_first[i] = (opt & INDOPTION_NULLS_FIRST) != 0;
 				}
 			}
-			else if (indexRelation->rd_am->amcanorder)
+			else if (amroutine->amcanorder)
 			{
 				/*
 				 * Otherwise, identify the corresponding btree opfamilies by