Make age extension usable from shared_preload_libraries

When AGE is loaded via shared_preload_libraries, its hooks
(post_parse_analyze, set_rel_pathlist, object_access) are active
before CREATE EXTENSION age is run. This causes errors when
non-Cypher queries trigger those hooks and ag_catalog does not
yet exist.

Changes:

- Add is_age_extension_exist() with a relcache callback cache so that
  checking pg_extension is not repeated on every hook invocation.
- Guard post_parse_analyze, set_rel_pathlist, and object_access hooks
  with is_age_extension_exist() so they become no-ops when the
  extension is not installed.
- Refactor ag_ProcessUtility_hook to detect CREATE/DROP EXTENSION age
  and broadcast a relcache invalidation via
  CacheInvalidateRelcacheByRelid(ExtensionRelationId) so other
  backends update their cached extension state.
- Wrap DROP EXTENSION processing in PG_TRY/PG_CATCH to restore
  object_access_hook if the drop fails (e.g. dependent objects).
- Skip _PG_init during pg_upgrade (IsBinaryUpgrade) to avoid hook
  registration when the binary-upgrade machinery is running.
- Add regression tests that verify hooks do not error when ag_catalog
  schema is absent.

Author: serdarmumcu

regress/expected/cypher_vle.out

@@ -1219,6 +1219,8 @@ NOTICE:  graph "cypher_vle" has been dropped
 
 (1 row)
 
+DROP FUNCTION prepend_node(text, text);
+DROP FUNCTION create_list(text);
 --
 -- End
 --

regress/expected/drop.out

@@ -40,6 +40,12 @@ SELECT tablename FROM pg_catalog.pg_tables WHERE schemaname = 'ag_catalog';
 -----------
 (0 rows)
 
+-- When ag_catalog is missing extension hooks shouldn't fail with the
+-- ERROR  schema "ag_catalog" does not exist.
+-- It might happen when 'age' is loaded but extension isn't created yet.
+DROP SCHEMA ag_catalog;
+CREATE SCHEMA _regress_drop;
+DROP SCHEMA _regress_drop; -- shouldn't produce the ERROR
 -- Recreate the extension and validate we can recreate a graph
 CREATE EXTENSION age;
 SELECT create_graph('drop');
@@ -115,7 +121,7 @@ NOTICE:  label "issue_1305"."r" has been dropped
 (1 row)
 
 SELECT drop_label('issue_1305', 'r');
-ERROR:  rel_name not found for label "r"
+ERROR:  label "r" does not exist
 SELECT drop_label('issue_1305', 'n', false);
 NOTICE:  label "issue_1305"."n" has been dropped
  drop_label 
@@ -124,7 +130,20 @@ NOTICE:  label "issue_1305"."n" has been dropped
 (1 row)
 
 SELECT drop_label('issue_1305', 'n');
-ERROR:  rel_name not found for label "n"
+ERROR:  label "n" does not exist
+-- Validate that labels are removed and tables are dropped
+select COUNT(*) FROM ag_label WHERE name IN ('n', 'r');
+ count 
+-------
+     0
+(1 row)
+
+SELECT COUNT(*) FROM pg_catalog.pg_tables WHERE schemaname = 'issue_1305' AND tablename IN ('n', 'r');
+ count 
+-------
+     0
+(1 row)
+
 SELECT * FROM drop_graph('issue_1305', true);
 NOTICE:  drop cascades to 2 other objects
 DETAIL:  drop cascades to table issue_1305._ag_label_vertex

regress/sql/cypher_vle.sql

@@ -418,6 +418,8 @@ DROP TABLE start_and_end_points;
 
 SELECT drop_graph('cypher_vle', true);
 
+DROP FUNCTION prepend_node(text, text);
+DROP FUNCTION create_list(text);
 --
 -- End
 --

regress/sql/drop.sql

@@ -28,6 +28,13 @@ SELECT nspname FROM pg_catalog.pg_namespace WHERE nspname = 'drop';
 
 SELECT tablename FROM pg_catalog.pg_tables WHERE schemaname = 'ag_catalog';
 
+-- When ag_catalog is missing extension hooks shouldn't fail with the
+-- ERROR  schema "ag_catalog" does not exist.
+-- It might happen when 'age' is loaded but extension isn't created yet.
+DROP SCHEMA ag_catalog;
+CREATE SCHEMA _regress_drop;
+DROP SCHEMA _regress_drop; -- shouldn't produce the ERROR
+
 -- Recreate the extension and validate we can recreate a graph
 CREATE EXTENSION age;
 
@@ -61,6 +68,11 @@ SELECT drop_label('issue_1305', 'r', false);
 SELECT drop_label('issue_1305', 'r');
 SELECT drop_label('issue_1305', 'n', false);
 SELECT drop_label('issue_1305', 'n');
+
+-- Validate that labels are removed and tables are dropped
+select COUNT(*) FROM ag_label WHERE name IN ('n', 'r');
+SELECT COUNT(*) FROM pg_catalog.pg_tables WHERE schemaname = 'issue_1305' AND tablename IN ('n', 'r');
+
 SELECT * FROM drop_graph('issue_1305', true);
 
 -- END

src/backend/age.c

@@ -17,6 +17,9 @@
  * under the License.
  */
 
+#include "postgres.h"
+#include "miscadmin.h"
+
 #include "catalog/ag_catalog.h"
 #include "nodes/ag_nodes.h"
 #include "optimizer/cypher_paths.h"
@@ -25,7 +28,6 @@
 #include "utils/age_global_graph.h"
 
 #if PG_VERSION_NUM < 170000
-#include "miscadmin.h"
 
 /* saved hook pointers for PG < 17 shmem path */
 static shmem_request_hook_type prev_shmem_request_hook = NULL;
@@ -56,6 +58,9 @@ void _PG_init(void);
 
 void _PG_init(void)
 {
+    if (IsBinaryUpgrade)
+        return;
+
     register_ag_nodes();
     set_rel_pathlist_init();
     object_access_hook_init();