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Improve DROP SERVER handling of dependent subscriptions.

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We do not allow a DROP SERVER ... CASCADE to implicitly drop a
subscription, because it's in a shared catalog and dropping a
subscription has side effects. Instead we throw an error and the user
must drop the subscription explicitly. Document this behavior and add
a HINT to the error message.

Generalize AcquireDeletionLock()/ReleaseDeletionLock() to use shared
object locks for all shared catalogs, which includes AuthMemRelationId
and now SubscriptionRelationId.

Move error message after AcquireDeletionLock() to avoid an unnecessary
error if there's a concurrent DROP SUBSCRIPTION.

Addresses finding 10 & 15 in report from linked discussion.

Reported-by: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/20260710195902.4f.noahmisch@microsoft.com
Backpatch-through: 19
This commit is contained in:
Jeff Davis
2026-08-03 13:21:46 -07:00
parent b48caa7dfd
commit b66ea17a3a
4 changed files with 28 additions and 13 deletions
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4
doc/src/sgml/ref/drop_server.sgml
View File

@@ -66,6 +66,10 @@ DROP SERVER [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [, .
user mappings),
and in turn all objects that depend on those objects
(see <xref linkend="ddl-depend"/>).
However, a subscription that uses the server is never dropped
automatically; it must be dropped with
<link linkend="sql-dropsubscription"><command>DROP SUBSCRIPTION</command></link>
before the server can be dropped.
</para>
</listitem>
</varlistentry>

31
src/backend/catalog/dependency.c
View File

@@ -900,17 +900,6 @@ findDependentObjects(const ObjectAddress *object,
object->objectSubId == 0)
continue;
/*
* Check that the dependent object is not in a shared catalog, which
* is not supported by doDeletion().
*/
if (IsSharedRelation(otherObject.classId))
ereport(ERROR,
(errcode(ERRCODE_DEPENDENT_OBJECTS_STILL_EXIST),
errmsg("cannot drop %s because %s depends on it",
getObjectDescription(object, false),
getObjectDescription(&otherObject, false))));
/*
* Must lock the dependent object before recursing to it.
*/
@@ -931,6 +920,22 @@ findDependentObjects(const ObjectAddress *object,
continue;
}
/*
* Check that the dependent object is not in a shared catalog, which
* is not supported by doDeletion().
*/
if (IsSharedRelation(otherObject.classId))
{
char *otherObjDesc = getObjectDescription(&otherObject,
false);
ereport(ERROR,
(errcode(ERRCODE_DEPENDENT_OBJECTS_STILL_EXIST),
errmsg("cannot drop %s because %s depends on it",
getObjectDescription(object, false), otherObjDesc),
errhint("Drop %s first.", otherObjDesc)));
}
/*
* We do need to delete it, so identify objflags to be passed down,
* which depend on the dependency type.
@@ -1579,7 +1584,7 @@ AcquireDeletionLock(const ObjectAddress *object, int flags)
else
LockRelationOid(object->objectId, AccessExclusiveLock);
}
else if (object->classId == AuthMemRelationId)
else if (IsSharedRelation(object->classId))
LockSharedObject(object->classId, object->objectId, 0,
AccessExclusiveLock);
else
@@ -1600,7 +1605,7 @@ ReleaseDeletionLock(const ObjectAddress *object)
{
if (object->classId == RelationRelationId)
UnlockRelationOid(object->objectId, AccessExclusiveLock);
else if (object->classId == AuthMemRelationId)
else if (IsSharedRelation(object->classId))
UnlockSharedObject(object->classId, object->objectId, 0,
AccessExclusiveLock);
else

4
src/test/regress/expected/subscription.out
View File

@@ -205,6 +205,10 @@ ALTER FOREIGN DATA WRAPPER test_fdw CONNECTION test_fdw_connection;
WARNING: changing the foreign-data wrapper connection function can cause the options for dependent objects to become invalid
DROP USER MAPPING FOR regress_subscription_user2 SERVER test_server;
REVOKE USAGE ON FOREIGN SERVER test_server FROM regress_subscription_user2;
-- fail, subscription depends on the server and cannot be dropped by CASCADE
DROP SERVER test_server CASCADE;
ERROR: cannot drop server test_server because subscription regress_testsub6 depends on it
HINT: Drop subscription regress_testsub6 first.
REVOKE USAGE ON FOREIGN SERVER test_server FROM regress_subscription_user3;
SET SESSION AUTHORIZATION regress_subscription_user3;
-- ok, lacks USAGE on test_server, but replacing connection anyway

2
src/test/regress/sql/subscription.sql
View File

@@ -150,6 +150,8 @@ ALTER SUBSCRIPTION regress_testsub6 OWNER TO regress_subscription_user2;
ALTER FOREIGN DATA WRAPPER test_fdw CONNECTION test_fdw_connection;
DROP USER MAPPING FOR regress_subscription_user2 SERVER test_server;
REVOKE USAGE ON FOREIGN SERVER test_server FROM regress_subscription_user2;
-- fail, subscription depends on the server and cannot be dropped by CASCADE
DROP SERVER test_server CASCADE;
REVOKE USAGE ON FOREIGN SERVER test_server FROM regress_subscription_user3;
SET SESSION AUTHORIZATION regress_subscription_user3;