tableam: introduce table AM infrastructure.

This introduces the concept of table access methods, i.e. CREATE
  ACCESS METHOD ... TYPE TABLE and
  CREATE TABLE ... USING (storage-engine).
No table access functionality is delegated to table AMs as of this
commit, that'll be done in following commits.

Subsequent commits will incrementally abstract table access
functionality to be routed through table access methods. That change
is too large to be reviewed & committed at once, so it'll be done
incrementally.

Docs will be updated at the end, as adding them incrementally would
likely make them less coherent, and definitely is a lot more work,
without a lot of benefit.

Table access methods are specified similar to index access methods,
i.e. pg_am.amhandler returns, as INTERNAL, a pointer to a struct with
callbacks. In contrast to index AMs that struct needs to live as long
as a backend, typically that's achieved by just returning a pointer to
a constant struct.

Psql's \d+ now displays a table's access method. That can be disabled
with HIDE_TABLEAM=true, which is mainly useful so regression tests can
be run against different AMs.  It's quite possible that this behaviour
still needs to be fine tuned.

For now it's not allowed to set a table AM for a partitioned table, as
we've not resolved how partitions would inherit that. Disallowing
allows us to introduce, if we decide that's the way forward, such a
behaviour without a compatibility break.

Catversion bumped, to add the heap table AM and references to it.

Author: Haribabu Kommi, Andres Freund, Alvaro Herrera, Dimitri Golgov and others
Discussion:
    https://postgr.es/m/20180703070645.wchpu5muyto5n647@alap3.anarazel.de
    https://postgr.es/m/20160812231527.GA690404@alvherre.pgsql
    https://postgr.es/m/20190107235616.6lur25ph22u5u5av@alap3.anarazel.de
    https://postgr.es/m/20190304234700.w5tmhducs5wxgzls@alap3.anarazel.de

1 files changed, 18 insertions, 10 deletions

diff --git a/src/backend/commands/amcmds.c b/src/backend/commands/amcmds.c
index c84507b5d03..24ca18018e1 100644
--- a/src/backend/commands/amcmds.c
+++ b/src/backend/commands/amcmds.c
@@ -30,7 +30,7 @@
 #include "utils/syscache.h"
 
 
-static Oid	lookup_index_am_handler_func(List *handler_name, char amtype);
+static Oid	lookup_am_handler_func(List *handler_name, char amtype);
 static const char *get_am_type_string(char amtype);
 
 
@@ -74,7 +74,7 @@ CreateAccessMethod(CreateAmStmt *stmt)
 	/*
 	 * Get the handler function oid, verifying the AM type while at it.
 	 */
-	amhandler = lookup_index_am_handler_func(stmt->handler_name, stmt->amtype);
+	amhandler = lookup_am_handler_func(stmt->handler_name, stmt->amtype);
 
 	/*
 	 * Insert tuple into pg_am.
@@ -229,6 +229,8 @@ get_am_type_string(char amtype)
 	{
 		case AMTYPE_INDEX:
 			return "INDEX";
+		case AMTYPE_TABLE:
+			return "TABLE";
 		default:
 			/* shouldn't happen */
 			elog(ERROR, "invalid access method type '%c'", amtype);
@@ -243,10 +245,11 @@ get_am_type_string(char amtype)
  * This function either return valid function Oid or throw an error.
  */
 static Oid
-lookup_index_am_handler_func(List *handler_name, char amtype)
+lookup_am_handler_func(List *handler_name, char amtype)
 {
 	Oid			handlerOid;
-	static const Oid funcargtypes[1] = {INTERNALOID};
+	Oid			funcargtypes[1] = {INTERNALOID};
+	Oid			expectedType = InvalidOid;
 
 	if (handler_name == NIL)
 		ereport(ERROR,
@@ -260,16 +263,21 @@ lookup_index_am_handler_func(List *handler_name, char amtype)
 	switch (amtype)
 	{
 		case AMTYPE_INDEX:
-			if (get_func_rettype(handlerOid) != INDEX_AM_HANDLEROID)
-				ereport(ERROR,
-						(errcode(ERRCODE_WRONG_OBJECT_TYPE),
-						 errmsg("function %s must return type %s",
-								NameListToString(handler_name),
-								"index_am_handler")));
+			expectedType = INDEX_AM_HANDLEROID;
+			break;
+		case AMTYPE_TABLE:
+			expectedType = TABLE_AM_HANDLEROID;
 			break;
 		default:
 			elog(ERROR, "unrecognized access method type \"%c\"", amtype);
 	}
 
+	if (get_func_rettype(handlerOid) != expectedType)
+		ereport(ERROR,
+				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+				 errmsg("function %s must return type %s",
+						get_func_name(handlerOid),
+						format_type_extended(expectedType, -1, 0))));
+
 	return handlerOid;
 }