Harden tableam against nonexistant / wrong kind of AMs.

Previously it was allowed to set default_table_access_method to an
empty string. That makes sense for default_tablespace, where that was
copied from, as it signals falling back to the database's default
tablespace. As there is no equivalent for table AMs, forbid that.

Also make sure to throw a usable error when creating a table using an
index AM, by using get_am_type_oid() to implement get_table_am_oid()
instead of a separate copy. Previously we'd error out only later, in
GetTableAmRoutine().

Thirdly remove GetTableAmRoutineByAmId() - it was only used in an
earlier version of 8586bf7ed8.

Add tests for the above (some for index AMs as well).

src/backend/access/table/tableamapi.c

@@ -17,14 +17,12 @@
 #include "access/xact.h"
 #include "catalog/pg_am.h"
 #include "catalog/pg_proc.h"
+#include "commands/defrem.h"
 #include "utils/fmgroids.h"
 #include "utils/memutils.h"
 #include "utils/syscache.h"
 
 
-static Oid	get_table_am_oid(const char *tableamname, bool missing_ok);
-
-
 /*
  * GetTableAmRoutine
  *		Call the specified access method handler routine to get its
@@ -41,7 +39,7 @@ GetTableAmRoutine(Oid amhandler)
 	routine = (TableAmRoutine *) DatumGetPointer(datum);
 
 	if (routine == NULL || !IsA(routine, TableAmRoutine))
-		elog(ERROR, "Table access method handler %u did not return a TableAmRoutine struct",
+		elog(ERROR, "table access method handler %u did not return a TableAmRoutine struct",
 			 amhandler);
 
 	/*
@@ -98,106 +96,30 @@ GetTableAmRoutine(Oid amhandler)
 	return routine;
 }
 
-/*
- * GetTableAmRoutineByAmId - look up the handler of the table access
- * method with the given OID, and get its TableAmRoutine struct.
- */
-const TableAmRoutine *
-GetTableAmRoutineByAmId(Oid amoid)
-{
-	regproc		amhandler;
-	HeapTuple	tuple;
-	Form_pg_am	amform;
-
-	/* Get handler function OID for the access method */
-	tuple = SearchSysCache1(AMOID, ObjectIdGetDatum(amoid));
-	if (!HeapTupleIsValid(tuple))
-		elog(ERROR, "cache lookup failed for access method %u",
-			 amoid);
-	amform = (Form_pg_am) GETSTRUCT(tuple);
-
-	/* Check that it is a table access method */
-	if (amform->amtype != AMTYPE_TABLE)
-		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("access method \"%s\" is not of type %s",
-						NameStr(amform->amname), "TABLE")));
-
-	amhandler = amform->amhandler;
-
-	/* Complain if handler OID is invalid */
-	if (!RegProcedureIsValid(amhandler))
-		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("table access method \"%s\" does not have a handler",
-						NameStr(amform->amname))));
-
-	ReleaseSysCache(tuple);
-
-	/* And finally, call the handler function to get the API struct. */
-	return GetTableAmRoutine(amhandler);
-}
-
-/*
- * get_table_am_oid - given a table access method name, look up the OID
- *
- * If missing_ok is false, throw an error if table access method name not
- * found. If true, just return InvalidOid.
- */
-static Oid
-get_table_am_oid(const char *tableamname, bool missing_ok)
-{
-	Oid			result;
-	Relation	rel;
-	TableScanDesc scandesc;
-	HeapTuple	tuple;
-	ScanKeyData entry[1];
-
-	/*
-	 * Search pg_am.  We use a heapscan here even though there is an index on
-	 * name, on the theory that pg_am will usually have just a few entries and
-	 * so an indexed lookup is a waste of effort.
-	 */
-	rel = heap_open(AccessMethodRelationId, AccessShareLock);
-
-	ScanKeyInit(&entry[0],
-				Anum_pg_am_amname,
-				BTEqualStrategyNumber, F_NAMEEQ,
-				CStringGetDatum(tableamname));
-	scandesc = table_beginscan_catalog(rel, 1, entry);
-	tuple = heap_getnext(scandesc, ForwardScanDirection);
-
-	/* We assume that there can be at most one matching tuple */
-	if (HeapTupleIsValid(tuple) &&
-		((Form_pg_am) GETSTRUCT(tuple))->amtype == AMTYPE_TABLE)
-		result = ((Form_pg_am) GETSTRUCT(tuple))->oid;
-	else
-		result = InvalidOid;
-
-	table_endscan(scandesc);
-	heap_close(rel, AccessShareLock);
-
-	if (!OidIsValid(result) && !missing_ok)
-		ereport(ERROR,
-				(errcode(ERRCODE_UNDEFINED_OBJECT),
-				 errmsg("table access method \"%s\" does not exist",
-						tableamname)));
-
-	return result;
-}
-
 /* check_hook: validate new default_table_access_method */
 bool
 check_default_table_access_method(char **newval, void **extra, GucSource source)
 {
+	if (**newval == '\0')
+	{
+		GUC_check_errdetail("default_table_access_method may not be empty.");
+		return false;
+	}
+
+	if (strlen(*newval) >= NAMEDATALEN)
+	{
+		GUC_check_errdetail("default_table_access_method is too long (maximum %d characters).",
+							NAMEDATALEN - 1);
+		return false;
+	}
+
 	/*
 	 * If we aren't inside a transaction, we cannot do database access so
 	 * cannot verify the name.  Must accept the value on faith.
 	 */
 	if (IsTransactionState())
 	{
-		if (**newval != '\0' &&
-			!OidIsValid(get_table_am_oid(*newval, true)))
+		if (!OidIsValid(get_table_am_oid(*newval, true)))
 		{
 			/*
 			 * When source == PGC_S_TEST, don't throw a hard error for a

src/backend/commands/amcmds.c

@@ -189,6 +189,16 @@ get_index_am_oid(const char *amname, bool missing_ok)
 	return get_am_type_oid(amname, AMTYPE_INDEX, missing_ok);
 }
 
+/*
+ * get_table_am_oid - given an access method name, look up its OID
+ *		and verify it corresponds to an table AM.
+ */
+Oid
+get_table_am_oid(const char *amname, bool missing_ok)
+{
+	return get_am_type_oid(amname, AMTYPE_TABLE, missing_ok);
+}
+
 /*
  * get_am_oid - given an access method name, look up its OID.
  *		The type is not checked.

src/backend/commands/tablecmds.c

@@ -832,22 +832,9 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 			 relkind == RELKIND_MATVIEW)
 		accessMethod = default_table_access_method;
 
-	/*
-	 * look up the access method, verify it can handle the requested features
-	 */
+	/* look up the access method, verify it is for a table */
 	if (accessMethod != NULL)
-	{
-		HeapTuple	tuple;
-
-		tuple = SearchSysCache1(AMNAME, PointerGetDatum(accessMethod));
-		if (!HeapTupleIsValid(tuple))
-				ereport(ERROR,
-						(errcode(ERRCODE_UNDEFINED_OBJECT),
-						 errmsg("table access method \"%s\" does not exist",
-								 accessMethod)));
-		accessMethodId = ((Form_pg_am) GETSTRUCT(tuple))->oid;
-		ReleaseSysCache(tuple);
-	}
+		accessMethodId = get_table_am_oid(accessMethod, false);
 
 	/*
 	 * Create the relation.  Inherited defaults and constraints are passed in

src/include/access/tableam.h

@@ -1616,7 +1616,6 @@ extern void table_block_parallelscan_startblock_init(Relation rel,
  */
 
 extern const TableAmRoutine *GetTableAmRoutine(Oid amhandler);
-extern const TableAmRoutine *GetTableAmRoutineByAmId(Oid amoid);
 extern const TableAmRoutine *GetHeapamTableAmRoutine(void);
 extern bool check_default_table_access_method(char **newval, void **extra,
 								  GucSource source);

src/include/commands/defrem.h

@@ -156,6 +156,7 @@ extern Datum transformGenericOptions(Oid catalogId,
 extern ObjectAddress CreateAccessMethod(CreateAmStmt *stmt);
 extern void RemoveAccessMethodById(Oid amOid);
 extern Oid	get_index_am_oid(const char *amname, bool missing_ok);
+extern Oid	get_table_am_oid(const char *amname, bool missing_ok);
 extern Oid	get_am_oid(const char *amname, bool missing_ok);
 extern char *get_am_name(Oid amOid);
 

src/test/regress/expected/create_am.out

@@ -3,6 +3,11 @@
 --
 -- Make gist2 over gisthandler. In fact, it would be a synonym to gist.
 CREATE ACCESS METHOD gist2 TYPE INDEX HANDLER gisthandler;
+-- Verify return type checks for handlers
+CREATE ACCESS METHOD bogus TYPE INDEX HANDLER int4in;
+ERROR:  function int4in(internal) does not exist
+CREATE ACCESS METHOD bogus TYPE INDEX HANDLER heap_tableam_handler;
+ERROR:  function heap_tableam_handler must return type index_am_handler
 -- Try to create gist2 index on fast_emp4000: fail because opclass doesn't exist
 CREATE INDEX grect2ind2 ON fast_emp4000 USING gist2 (home_base);
 ERROR:  data type box has no default operator class for access method "gist2"
@@ -102,8 +107,24 @@ NOTICE:  drop cascades to index grect2ind2
 --
 -- Test table access methods
 --
+-- prevent empty values
+SET default_table_access_method = '';
+ERROR:  invalid value for parameter "default_table_access_method": ""
+DETAIL:  default_table_access_method may not be empty.
+-- prevent nonexistant values
+SET default_table_access_method = 'I do not exist AM';
+ERROR:  invalid value for parameter "default_table_access_method": "I do not exist AM"
+DETAIL:  Table access method "I do not exist AM" does not exist.
+-- prevent setting it to an index AM
+SET default_table_access_method = 'btree';
+ERROR:  access method "btree" is not of type TABLE
 -- Create a heap2 table am handler with heapam handler
 CREATE ACCESS METHOD heap2 TYPE TABLE HANDLER heap_tableam_handler;
+-- Verify return type checks for handlers
+CREATE ACCESS METHOD bogus TYPE TABLE HANDLER int4in;
+ERROR:  function int4in(internal) does not exist
+CREATE ACCESS METHOD bogus TYPE TABLE HANDLER bthandler;
+ERROR:  function bthandler must return type table_am_handler
 SELECT amname, amhandler, amtype FROM pg_am where amtype = 't' ORDER BY 1, 2;
  amname |      amhandler       | amtype 
 --------+----------------------+--------
@@ -253,6 +274,18 @@ ORDER BY 3, 1, 2;
 
 -- don't want to keep those tables, nor the default
 ROLLBACK;
+-- Third, check that we can neither create a table using a nonexistant
+-- AM, nor using an index AM
+CREATE TABLE i_am_a_failure() USING "";
+ERROR:  zero-length delimited identifier at or near """"
+LINE 1: CREATE TABLE i_am_a_failure() USING "";
+                                            ^
+CREATE TABLE i_am_a_failure() USING i_do_not_exist_am;
+ERROR:  access method "i_do_not_exist_am" does not exist
+CREATE TABLE i_am_a_failure() USING "I do not exist AM";
+ERROR:  access method "I do not exist AM" does not exist
+CREATE TABLE i_am_a_failure() USING "btree";
+ERROR:  access method "btree" is not of type TABLE
 -- Drop table access method, which fails as objects depends on it
 DROP ACCESS METHOD heap2;
 ERROR:  cannot drop access method heap2 because other objects depend on it

src/test/regress/expected/type_sanity.out

@@ -520,6 +520,24 @@ WHERE p1.relkind IN ('S', 'v', 'f', 'c') and
 -----+---------
 (0 rows)
 
+-- Indexes should have AMs of type 'i'
+SELECT pc.oid, pc.relname, pa.amname, pa.amtype
+FROM pg_class as pc JOIN pg_am AS pa ON (pc.relam = pa.oid)
+WHERE pc.relkind IN ('i') and
+    pa.amtype != 'i';
+ oid | relname | amname | amtype 
+-----+---------+--------+--------
+(0 rows)
+
+-- Tables, matviews etc should have AMs of type 't'
+SELECT pc.oid, pc.relname, pa.amname, pa.amtype
+FROM pg_class as pc JOIN pg_am AS pa ON (pc.relam = pa.oid)
+WHERE pc.relkind IN ('r', 't', 'm') and
+    pa.amtype != 't';
+ oid | relname | amname | amtype 
+-----+---------+--------+--------
+(0 rows)
+
 -- **************** pg_attribute ****************
 -- Look for illegal values in pg_attribute fields
 SELECT p1.attrelid, p1.attname

src/test/regress/sql/create_am.sql

@@ -5,6 +5,11 @@
 -- Make gist2 over gisthandler. In fact, it would be a synonym to gist.
 CREATE ACCESS METHOD gist2 TYPE INDEX HANDLER gisthandler;
 
+-- Verify return type checks for handlers
+CREATE ACCESS METHOD bogus TYPE INDEX HANDLER int4in;
+CREATE ACCESS METHOD bogus TYPE INDEX HANDLER heap_tableam_handler;
+
+
 -- Try to create gist2 index on fast_emp4000: fail because opclass doesn't exist
 CREATE INDEX grect2ind2 ON fast_emp4000 USING gist2 (home_base);
 
@@ -72,11 +77,26 @@ DROP ACCESS METHOD gist2 CASCADE;
 -- Test table access methods
 --
 
+-- prevent empty values
+SET default_table_access_method = '';
+
+-- prevent nonexistant values
+SET default_table_access_method = 'I do not exist AM';
+
+-- prevent setting it to an index AM
+SET default_table_access_method = 'btree';
+
+
 -- Create a heap2 table am handler with heapam handler
 CREATE ACCESS METHOD heap2 TYPE TABLE HANDLER heap_tableam_handler;
 
+-- Verify return type checks for handlers
+CREATE ACCESS METHOD bogus TYPE TABLE HANDLER int4in;
+CREATE ACCESS METHOD bogus TYPE TABLE HANDLER bthandler;
+
 SELECT amname, amhandler, amtype FROM pg_am where amtype = 't' ORDER BY 1, 2;
 
+
 -- First create tables employing the new AM using USING
 
 -- plain CREATE TABLE
@@ -178,6 +198,13 @@ ORDER BY 3, 1, 2;
 -- don't want to keep those tables, nor the default
 ROLLBACK;
 
+-- Third, check that we can neither create a table using a nonexistant
+-- AM, nor using an index AM
+CREATE TABLE i_am_a_failure() USING "";
+CREATE TABLE i_am_a_failure() USING i_do_not_exist_am;
+CREATE TABLE i_am_a_failure() USING "I do not exist AM";
+CREATE TABLE i_am_a_failure() USING "btree";
+
 -- Drop table access method, which fails as objects depends on it
 DROP ACCESS METHOD heap2;
 

src/test/regress/sql/type_sanity.sql

@@ -379,6 +379,18 @@ FROM pg_class as p1
 WHERE p1.relkind IN ('S', 'v', 'f', 'c') and
     p1.relam != 0;
 
+-- Indexes should have AMs of type 'i'
+SELECT pc.oid, pc.relname, pa.amname, pa.amtype
+FROM pg_class as pc JOIN pg_am AS pa ON (pc.relam = pa.oid)
+WHERE pc.relkind IN ('i') and
+    pa.amtype != 'i';
+
+-- Tables, matviews etc should have AMs of type 't'
+SELECT pc.oid, pc.relname, pa.amname, pa.amtype
+FROM pg_class as pc JOIN pg_am AS pa ON (pc.relam = pa.oid)
+WHERE pc.relkind IN ('r', 't', 'm') and
+    pa.amtype != 't';
+
 -- **************** pg_attribute ****************
 
 -- Look for illegal values in pg_attribute fields