Heed lock protocol in DROP OWNED BY

We were acquiring object locks then deleting objects one by one, instead
of acquiring all object locks first, ignoring those that did not exist,
and then deleting all objects together.   The latter is the correct
protocol to use, and what this commits changes to code to do.  Failing
to follow that leads to "cache lookup failed for relation XYZ" error
reports when DROP OWNED runs concurrently with other DDL -- for example,
a session termination that removes some temp tables.

Author: Álvaro Herrera
Reported-by: Mithun Chicklore Yogendra (Mithun CY)
Reviewed-by: Ahsan Hadi, Tom Lane
Discussion: https://postgr.es/m/CADq3xVZTbzK4ZLKq+dn_vB4QafXXbmMgDP3trY-GuLnib2Ai1w@mail.gmail.com

diff --git a/src/backend/catalog/dependency.c b/src/backend/catalog/dependency.c
index ffd52c11533e3a1f05e76c3aa8194c2b3dd2de80..5565e6fc197d54bf2aaee174c70d7fc5640e0ec7 100644 (file)
--- a/src/backend/catalog/dependency.c
+++ b/src/backend/catalog/dependency.c
@@ -200,8 +200,6 @@ static void reportDependentObjects(const ObjectAddresses *targetObjects,
 static void deleteOneObject(const ObjectAddress *object,
                            Relation *depRel, int32 flags);
 static void doDeletion(const ObjectAddress *object, int flags);
-static void AcquireDeletionLock(const ObjectAddress *object, int flags);
-static void ReleaseDeletionLock(const ObjectAddress *object);
 static bool find_expr_references_walker(Node *node,
                                        find_expr_references_context *context);
 static void eliminate_duplicate_dependencies(ObjectAddresses *addrs);
@@ -1527,11 +1525,14 @@ doDeletion(const ObjectAddress *object, int flags)
 /*
  * AcquireDeletionLock - acquire a suitable lock for deleting an object
  *
+ * Accepts the same flags as performDeletion (though currently only
+ * PERFORM_DELETION_CONCURRENTLY does anything).
+ *
  * We use LockRelation for relations, LockDatabaseObject for everything
- * else.  Note that dependency.c is not concerned with deleting any kind of
- * shared-across-databases object, so we have no need for LockSharedObject.
+ * else.  Shared-across-databases objects are not currently supported
+ * because no caller cares, but could be modified to use LockSharedObject.
  */
-static void
+void
 AcquireDeletionLock(const ObjectAddress *object, int flags)
 {
    if (object->classId == RelationRelationId)
@@ -1557,8 +1558,10 @@ AcquireDeletionLock(const ObjectAddress *object, int flags)
 
 /*
  * ReleaseDeletionLock - release an object deletion lock
+ *
+ * Companion to AcquireDeletionLock.
  */
-static void
+void
 ReleaseDeletionLock(const ObjectAddress *object)
 {
    if (object->classId == RelationRelationId)

diff --git a/src/backend/catalog/pg_shdepend.c b/src/backend/catalog/pg_shdepend.c
index 2ef792dbd768bd5776a5b80b683c8552a225a60a..61447f33a699df01da277da69293616ea9a86bdb 100644 (file)
--- a/src/backend/catalog/pg_shdepend.c
+++ b/src/backend/catalog/pg_shdepend.c
@@ -1324,7 +1324,10 @@ shdepDropOwned(List *roleids, DropBehavior behavior)
                                            sdepForm->objid);
                    break;
                case SHARED_DEPENDENCY_POLICY:
-                   /* If unable to remove role from policy, remove policy. */
+                   /*
+                    * Try to remove role from policy; if unable to, remove
+                    * policy.
+                    */
                    if (!RemoveRoleFromObjectPolicy(roleid,
                                                    sdepForm->classid,
                                                    sdepForm->objid))
@@ -1332,6 +1335,18 @@ shdepDropOwned(List *roleids, DropBehavior behavior)
                        obj.classId = sdepForm->classid;
                        obj.objectId = sdepForm->objid;
                        obj.objectSubId = sdepForm->objsubid;
+                       /*
+                        * Acquire lock on object, then verify this dependency
+                        * is still relevant.  If not, the object might have
+                        * been dropped or the policy modified.  Ignore the
+                        * object in that case.
+                        */
+                       AcquireDeletionLock(&obj, 0);
+                       if (!systable_recheck_tuple(scan, tuple))
+                       {
+                           ReleaseDeletionLock(&obj);
+                           break;
+                       }
                        add_exact_object_address(&obj, deleteobjs);
                    }
                    break;
@@ -1342,6 +1357,13 @@ shdepDropOwned(List *roleids, DropBehavior behavior)
                        obj.classId = sdepForm->classid;
                        obj.objectId = sdepForm->objid;
                        obj.objectSubId = sdepForm->objsubid;
+                       /* as above */
+                       AcquireDeletionLock(&obj, 0);
+                       if (!systable_recheck_tuple(scan, tuple))
+                       {
+                           ReleaseDeletionLock(&obj);
+                           break;
+                       }
                        add_exact_object_address(&obj, deleteobjs);
                    }
                    break;

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 7f156673f7d7466730458b5445b4da3acb708cce..9ebb026187f7503419ba97215c2cb804d7a39b02 100644 (file)
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -915,7 +915,6 @@ DropSubscription(DropSubscriptionStmt *stmt, bool isTopLevel)
    if (slotname)
        PreventInTransactionBlock(isTopLevel, "DROP SUBSCRIPTION");
 
-
    ObjectAddressSet(myself, SubscriptionRelationId, subid);
    EventTriggerSQLDropAddObject(&myself, true, true);
 

diff --git a/src/include/catalog/dependency.h b/src/include/catalog/dependency.h
index 2c6abe26a5ab9f925f2af7b83ca2ba0fd4f0841a..a8f7e9965b7c3eb9102f86540a8747760c6afee8 100644 (file)
--- a/src/include/catalog/dependency.h
+++ b/src/include/catalog/dependency.h
@@ -142,6 +142,10 @@ typedef enum ObjectClass
 
 /* in dependency.c */
 
+extern void AcquireDeletionLock(const ObjectAddress *object, int flags);
+
+extern void ReleaseDeletionLock(const ObjectAddress *object);
+
 extern void performDeletion(const ObjectAddress *object,
                            DropBehavior behavior, int flags);