Support for weak binding views to allow dropping of underlying objects BABEL_4_X_DEV (babelfish-for-postgresql#3965)

* Support for weak binding views to allow dropping of underlying objects.This commit introduces support for both strong and weak view binding in Babelfish, aligning more closely with SQL Server's default behavior while maintaining flexibility. (babelfish-for-postgresql#3806)

Description
Currently, Babelfish only supports strong binding for views, which prevents dropping or altering referenced objects when views depend on them. This behavior differs from SQL Server, which by default allows dropping underlying tables or views unless WITH SCHEMABINDING is explicitly specified.
With this change, Babelfish now supports configurable view binding modes:

Strong binding (default): Prevents dropping referenced objects if views depend on them
Weak binding: Allows dropping of referenced objects
This feature aligns Babelfish more closely with SQL Server's behavior, providing greater flexibility
Key aspects include:

A new GUC parameter babelfishpg_tsql.weak_view_binding to control the default binding behavior (default is false)
Support for explicit WITH SCHEMABINDING to create strongly bound views regardless of the GUC setting
Ability to create weakly bound views by default when the GUC is enabled
Proper handling of ALTER VIEW operations in both binding modes
In SQL Server, views are weakly bound by default, allowing underlying objects to be dropped or altered. With our implementation, users can now choose between SQL Server's default behavior (weak binding) or the previously enforced behavior (strong binding).

Important Limitation :
This implementation currently only addresses DROP operations on tables, views, functions, procedures as well as ALTER operations on views when these objects are bound by dependent views. ALTER TABLE/ ALTER FUNCTION operations (such as dropping columns or changing data types) are still restricted when dependent views exist, regardless of binding mode. This differs from SQL Server's behavior, where weak binding also allows ALTER operations on referenced objects.
When the same underlying object is recreated, its broken child view will get repaired only if it follows postgresql restrictions for CREATE OR REPLACE VIEW. [The new query must generate the same columns that were generated by the existing view query (that is, the same column names in the same order and with the same data types), but it may add additional columns to the end of the list]
https://www.postgresql.org/docs/current/sql-createview.html#:~:text=The%20new%20query,be%20completely%20different.

Issues Resolved
BABEL-1660

* Fix crash during tuple update for broken view by registering an active transaction snapshot

---------

Signed-off-by: Rahul Parande <rparande@amazon.com>
Co-authored-by: Rahul Parande <rparande@amazon.com>

Author: 2 people

contrib/babelfishpg_tsql/runtime/functions.c

@@ -4482,8 +4482,14 @@ objectproperty_internal(PG_FUNCTION_ARGS)
 		 */
 		if (pg_strcasecmp(property, "isschemabound") == 0)
 		{
+			bool is_weak_view = false;
+			bool is_view = (type == OBJECT_TYPE_VIEW);
+
+			if (is_view)
+				check_is_tsql_view(object_id, &is_weak_view);
+
 			pfree(property);
-			PG_RETURN_INT32(0);
+			PG_RETURN_INT32(is_view ? ((int) !is_weak_view) : 0);
 		}
 		/*
 		 * For ExecIsQuotedIdentOn and ExecIsAnsiNullsOn, we hardcoded it to 1

contrib/babelfishpg_tsql/src/catalog.c

@@ -1198,17 +1198,40 @@ get_bbf_view_def_idx_oid()
 }
 
 HeapTuple
-search_bbf_view_def(Relation bbf_view_def_rel, int16 dbid, const char *logical_schema_name, const char *view_name)
+search_bbf_view_def(Relation bbf_view_def_rel, Oid viewOid)
 {
 
 	ScanKeyData scanKey[3];
 	SysScanDesc scan;
 	HeapTuple	scantup,
 				oldtup;
+	Oid 		schema_id;
+	char 		*schema_name = NULL;
+	char		*view_name = NULL;
+	const char  *logical_schema_name = NULL;
+	int16 		dbid = InvalidDbid;
 
-	if (!DbidIsValid(dbid) || logical_schema_name == NULL || view_name == NULL)
+	if (!OidIsValid(viewOid))
 		return NULL;
 
+	schema_id = get_rel_namespace(viewOid);
+	schema_name = get_namespace_name(schema_id);
+	view_name = get_rel_name(viewOid);
+	
+	if (!schema_name)
+		return NULL;
+	
+	logical_schema_name = get_logical_schema_name(schema_name, true);
+	dbid = get_dbid_from_physical_schema_name(schema_name, true);
+
+	if (!DbidIsValid(dbid) || logical_schema_name == NULL || view_name == NULL)
+	{
+		pfree(view_name);
+		pfree(schema_name);
+		if (logical_schema_name)
+			pfree((char *) logical_schema_name);
+		return NULL;
+	}
 
 	/* Search and drop the definition */
 	ScanKeyInit(&scanKey[0],
@@ -1238,7 +1261,7 @@ search_bbf_view_def(Relation bbf_view_def_rel, int16 dbid, const char *logical_s
 
 /* Checks if it is view created during v2.2.0 or after that */
 bool
-check_is_tsql_view(Oid relid)
+check_is_tsql_view(Oid relid, bool *is_weak_view)
 {
 	Oid			schema_oid;
 	Relation	bbf_view_def_rel;
@@ -1248,10 +1271,17 @@ check_is_tsql_view(Oid relid)
 	int16		logical_dbid;
 	const char *logical_schema_name;
 	bool		is_tsql_view = false;
+	bool 		bisnull;
+	Datum 		flag_values_datum;
+	uint64 		flag_values;
 
 	view_name = get_rel_name(relid);
 	schema_oid = get_rel_namespace(relid);
 	schema_name = get_namespace_name(schema_oid);
+
+	if (is_weak_view != NULL)
+		*is_weak_view = false;
+
 	if (view_name == NULL || schema_name == NULL || is_shared_schema(schema_name))
 	{
 		if (view_name)
@@ -1272,12 +1302,27 @@ check_is_tsql_view(Oid relid)
 	}
 	/* Fetch the relation */
 	bbf_view_def_rel = table_open(get_bbf_view_def_oid(), AccessShareLock);
-
-	scantup = search_bbf_view_def(bbf_view_def_rel, logical_dbid, logical_schema_name, view_name);
+	scantup = search_bbf_view_def(bbf_view_def_rel, relid);
 
 	if (HeapTupleIsValid(scantup))
 	{
 		is_tsql_view = true;
+
+		/* Check if the view is a weak bound view */
+		if (is_weak_view != NULL)
+		{
+			flag_values_datum = heap_getattr(scantup, 
+								Anum_bbf_view_def_flag_values,
+								RelationGetDescr(bbf_view_def_rel), 
+								&bisnull);
+			
+			if (!bisnull)
+			{
+				flag_values = DatumGetUInt64(flag_values_datum);
+				*is_weak_view = (flag_values & BBF_VIEW_DEF_FLAG_IS_WEAK_VIEW) != 0;
+			}
+		}
+
 		heap_freetuple(scantup);
 	}
 	table_close(bbf_view_def_rel, AccessShareLock);

contrib/babelfishpg_tsql/src/catalog.h

@@ -201,18 +201,22 @@ typedef FormData_authid_user_ext *Form_authid_user_ext;
 #define Anum_bbf_view_def_schema_name 2
 #define Anum_bbf_view_def_object_name 3
 #define Anum_bbf_view_def_definition 4
+#define Anum_bbf_view_def_flag_validity 5
+#define Anum_bbf_view_def_flag_values 6
 #define BBF_VIEW_DEF_NUM_COLS 8
 #define BBF_VIEW_DEF_FLAG_IS_ANSI_NULLS_ON (1<<0)
 #define BBF_VIEW_DEF_FLAG_USES_QUOTED_IDENTIFIER (1<<1)
 #define BBF_VIEW_DEF_FLAG_CREATED_IN_OR_AFTER_2_4 (0<<2)
+#define BBF_VIEW_DEF_FLAG_IS_WEAK_VIEW (1<<3)
+#define BBF_VIEW_DEF_FLAG_IS_BROKEN (1<<4)
+
 extern Oid	bbf_view_def_oid;
 extern Oid	bbf_view_def_idx_oid;
 
 extern Oid	get_bbf_view_def_oid(void);
 extern Oid	get_bbf_view_def_idx_oid(void);
-extern HeapTuple search_bbf_view_def(Relation bbf_view_def_rel, int16 dbid,
-									 const char *logical_schema_name, const char *view_name);
-extern bool check_is_tsql_view(Oid relid);
+extern HeapTuple search_bbf_view_def(Relation bbf_view_def_rel, Oid viewOid);
+extern bool check_is_tsql_view(Oid relid, bool *is_weak_view);
 extern void clean_up_bbf_view_def(int16 dbid);
 extern void drop_bbf_schema_permission_entries(int16 dbid);
 

contrib/babelfishpg_tsql/src/guc.c

@@ -18,6 +18,7 @@
 #define PLTSQL_DEFAULT_LANGUAGE "us_english"
 
 static int	migration_mode = SINGLE_DB;
+bool		pltsql_weak_view_binding = false;
 bool		enable_ownership_structure = false;
 
 bool		enable_metadata_inconsistency_check = true;
@@ -630,6 +631,16 @@ define_custom_variables(void)
 							 GUC_NO_RESET_ALL,
 							 NULL, NULL, NULL);
 
+	DefineCustomBoolVariable("babelfishpg_tsql.weak_view_binding",
+							 gettext_noop("Sets the default binding mode for views."),
+							 gettext_noop("When set to false (default), views will bind to the schema of its underlying tables or other objects" 
+										  "When set to true, views created will have weak binding and are no longer bound to schema of its underlying" 
+										  "objects unless explicitly declared in create/alter DDL"),
+							 &pltsql_weak_view_binding,
+							 false,  /* Default is strong binding (false) */
+							 PGC_USERSET,
+							 GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_DISALLOW_IN_AUTO_FILE,
+							 NULL, NULL, NULL);
 
 	/* ANTLR parser */
 	DefineCustomBoolVariable("babelfishpg_tsql.dump_antlr_query_graph",

contrib/babelfishpg_tsql/src/guc.h

@@ -20,6 +20,7 @@ extern bool pltsql_enable_create_alter_view_from_pg;
 extern bool pltsql_enable_linked_servers;
 extern bool pltsql_allow_windows_login;
 extern bool pltsql_allow_fulltext_parser;
+extern bool pltsql_weak_view_binding;
 extern char *pltsql_psql_logical_babelfish_db_name;
 extern int  pltsql_isolation_level_repeatable_read;
 extern int  pltsql_isolation_level_serializable;