Prevent drop of tablespaces used by partitioned relations

When a tablespace is used in a partitioned relation (per commits
ca4103025dfe in pg12 for tables and 33e6c34c3267 in pg11 for indexes),
it is possible to drop the tablespace, potentially causing various
problems.  One such was reported in bug #16577, where a rewriting ALTER
TABLE causes a server crash.

Protect against this by using pg_shdepend to keep track of tablespaces
when used for relations that don't keep physical files; we now abort a
tablespace if we see that the tablespace is referenced from any
partitioned relations.

Backpatch this to 11, where this problem has been latent all along.  We
don't try to create pg_shdepend entries for existing partitioned
indexes/tables, but any ones that are modified going forward will be
protected.

Note slight behavior change: when trying to drop a tablespace that
contains both regular tables as well as partitioned ones, you'd
previously get ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE and now you'll
get ERRCODE_DEPENDENT_OBJECTS_STILL_EXIST.  Arguably, the latter is more
correct.

It is possible to add protecting pg_shdepend entries for existing
tables/indexes, by doing
  ALTER TABLE ONLY some_partitioned_table SET TABLESPACE pg_default;
  ALTER TABLE ONLY some_partitioned_table SET TABLESPACE original_tablespace;
for each partitioned table/index that is not in the database default
tablespace.  Because these partitioned objects do not have storage, no
file needs to be actually moved, so it shouldn't take more time than
what's required to acquire locks.

This query can be used to search for such relations:
SELECT ... FROM pg_class WHERE relkind IN ('p', 'I') AND reltablespace <> 0

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/16577-881633a9f9894fd5@postgresql.org
Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Michael Paquier <michael@paquier.xyz>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/include/catalog/dependency.h b/src/include/catalog/dependency.h
index a8f7e9965b7..7fe3fb7e7cf 100644
--- a/src/include/catalog/dependency.h
+++ b/src/include/catalog/dependency.h
@@ -67,6 +67,12 @@ typedef enum DependencyType
  * a role mentioned in a policy object.  The referenced object must be a
  * pg_authid entry.
  *
+ * (e) a SHARED_DEPENDENCY_TABLESPACE entry means that the referenced
+ * object is a tablespace mentioned in a relation without storage.  The
+ * referenced object must be a pg_tablespace entry.  (Relations that have
+ * storage don't need this: they are protected by the existence of a physical
+ * file in the tablespace.)
+ *
  * SHARED_DEPENDENCY_INVALID is a value used as a parameter in internal
  * routines, and is not valid in the catalog itself.
  */
@@ -76,6 +82,7 @@ typedef enum SharedDependencyType
 	SHARED_DEPENDENCY_OWNER = 'o',
 	SHARED_DEPENDENCY_ACL = 'a',
 	SHARED_DEPENDENCY_POLICY = 'r',
+	SHARED_DEPENDENCY_TABLESPACE = 't',
 	SHARED_DEPENDENCY_INVALID = 0
 } SharedDependencyType;
 
@@ -241,6 +248,12 @@ extern void recordDependencyOnOwner(Oid classId, Oid objectId, Oid owner);
 extern void changeDependencyOnOwner(Oid classId, Oid objectId,
 									Oid newOwnerId);
 
+extern void recordDependencyOnTablespace(Oid classId, Oid objectId,
+										 Oid tablespace);
+
+extern void changeDependencyOnTablespace(Oid classId, Oid objectId,
+										 Oid newTablespaceId);
+
 extern void updateAclDependencies(Oid classId, Oid objectId, int32 objectSubId,
 								  Oid ownerId,
 								  int noldmembers, Oid *oldmembers,