From 127b0c490c25c4c900543ec7b0e3261e1f7749b8 Mon Sep 17 00:00:00 2001 From: Bertrand Drouvot Date: Mon, 27 Apr 2026 14:01:46 +0000 Subject: [PATCH v20 1/3] Avoid orphaned objects dependencies Concurrent DDL can create orphaned dependencies in pg_depend, objects referencing other objects that no longer exist. For example: Scenario 1: session 1: begin; drop schema schem; session 2: create a function in the schema schem session 1: commit; With the above, the function created in session 2 would be linked to a non existing schema. Scenario 2: session 1: begin; create a function in the schema schem session 2: drop schema schem; session 1: commit; With the above, the function created in session 1 would be linked to a non existing schema. Fix by acquiring AccessShareLock on referenced objects when recording dependencies. This conflicts with AccessExclusiveLock taken by DROP, preventing the race. After acquiring the lock, verify the object still exists, if it was dropped concurrently, report an error. The lock and check is done in both recordMultipleDependencies() and changeDependencyFor(). The patch adds a few tests for some dependency cases (that would currently produce orphaned objects): - schema and function (as the above scenarios) - alter a dependency (function and schema) - function and arg type - function and return type - function and function - domain and domain - table and type - server and foreign data wrapper Author: Bertrand Drouvot Reviewed-by: Discussion: https://postgr.es/m/ZiYjn0eVc7pxVY45@ip-10-97-1-34.eu-west-3.compute.internal --- src/backend/catalog/dependency.c | 72 ++++++++++ src/backend/catalog/objectaddress.c | 65 +++++++++ src/backend/catalog/pg_depend.c | 16 ++- src/backend/utils/errcodes.txt | 1 + src/include/catalog/dependency.h | 2 + src/include/catalog/objectaddress.h | 1 + .../expected/test_dependencies_locks.out | 129 ++++++++++++++++++ src/test/isolation/isolation_schedule | 1 + .../specs/test_dependencies_locks.spec | 96 +++++++++++++ src/test/regress/expected/alter_table.out | 11 +- 10 files changed, 386 insertions(+), 8 deletions(-) 26.4% src/backend/catalog/ 41.3% src/test/isolation/expected/ 27.7% src/test/isolation/specs/ 4.3% src/ diff --git a/src/backend/catalog/dependency.c b/src/backend/catalog/dependency.c index fdb8e67e1f5..7e26691393d 100644 --- a/src/backend/catalog/dependency.c +++ b/src/backend/catalog/dependency.c @@ -87,6 +87,7 @@ #include "parser/parsetree.h" #include "rewrite/rewriteRemove.h" #include "storage/lmgr.h" +#include "storage/lock.h" #include "utils/fmgroids.h" #include "utils/lsyscache.h" #include "utils/syscache.h" @@ -1606,6 +1607,77 @@ ReleaseDeletionLock(const ObjectAddress *object) AccessExclusiveLock); } +/* + * LockNotPinnedObject + * + * Lock the object that we are about to record a dependency on. + * After it's locked, verify that it hasn't been dropped while we + * weren't looking. If the object has been dropped, this function + * does not return! + * + * If the caller already holds a lock that conflicts with DROP + * (AccessShareLock or stronger), skip the lock acquisition entirely. + */ +void +LockNotPinnedObject(const ObjectAddress *object) +{ + if (isObjectPinned(object)) + return; + + if (object->classId == RelationRelationId) + { + /* skip shared relations as they are pinned */ + if (IsSharedRelation(object->objectId)) + return; + + /* + * We must be in one of the two following cases that would already + * prevent the relation to be dropped: 1. The relation is already + * locked (could be an existing relation or a relation that we are + * creating). 2. The relation is protected indirectly (i.e an index + * protected by a lock on its table, a table protected by a lock on a + * function that depends of the table...). To avoid any risks, acquire + * a lock if there is none. That may add unnecessary lock for 2. but + * that's worth it. + */ + if (!CheckRelationOidLockedByMe(object->objectId, AccessShareLock, true)) + LockRelationOid(object->objectId, AccessShareLock); + return; + } + else + { + LOCKTAG tag; + + SET_LOCKTAG_OBJECT(tag, + MyDatabaseId, + object->classId, + object->objectId, + 0); + + if (LockHeldByMe(&tag, AccessShareLock, true)) + return; + + /* assume we should lock the whole object not a sub-object */ + LockDatabaseObject(object->classId, object->objectId, 0, AccessShareLock); + } + + /* check if object still exists */ + if (!ObjectByIdExist(object, false)) + { + /* + * It might be possible that we are creating it (for example creating + * a composite type while creating a relation), so bypass the syscache + * lookup and use a SnapshotSelf scan instead to cover this scenario. + */ + if (!ObjectByIdExist(object, true)) + ereport(ERROR, + (errcode(ERRCODE_DEPENDENT_OBJECTS_DOES_NOT_EXIST), + errmsg("dependent object does not exist"), + errdetail("Class OID is %u and object OID is %u", + object->classId, object->objectId))); + } +} + /* * recordDependencyOnExpr - find expression dependencies * diff --git a/src/backend/catalog/objectaddress.c b/src/backend/catalog/objectaddress.c index c1862809577..d1ed8188d93 100644 --- a/src/backend/catalog/objectaddress.c +++ b/src/backend/catalog/objectaddress.c @@ -90,6 +90,7 @@ #include "utils/lsyscache.h" #include "utils/memutils.h" #include "utils/regproc.h" +#include "utils/snapmgr.h" #include "utils/syscache.h" /* @@ -2696,6 +2697,70 @@ get_object_namespace(const ObjectAddress *address) return oid; } +/* + * ObjectByIdExist + * + * Return whether the given object exists. + * + * If use_snapshot_self is false, uses the syscache (which sees committed data). + * If use_snapshot_self is true, does a direct catalog scan with SnapshotSelf + * to also see objects created in the current transaction. + */ +bool +ObjectByIdExist(const ObjectAddress *address, bool use_snapshot_self) +{ + HeapTuple tuple; + SysCacheIdentifier cache = SYSCACHEID_INVALID; + + if (!use_snapshot_self) + { + const ObjectPropertyType *property; + + property = get_object_property_data(address->classId); + cache = property->oid_catcache_id; + } + + if (cache != SYSCACHEID_INVALID) + { + tuple = SearchSysCache1(cache, ObjectIdGetDatum(address->objectId)); + + if (!HeapTupleIsValid(tuple)) + return false; + + ReleaseSysCache(tuple); + return true; + } + else + { + Relation rel; + ScanKeyData skey[1]; + SysScanDesc scan; + Snapshot snapshot; + + if (use_snapshot_self) + snapshot = SnapshotSelf; + else + snapshot = NULL; + + rel = table_open(address->classId, AccessShareLock); + + ScanKeyInit(&skey[0], + get_object_attnum_oid(address->classId), + BTEqualStrategyNumber, F_OIDEQ, + ObjectIdGetDatum(address->objectId)); + + scan = systable_beginscan(rel, get_object_oid_index(address->classId), + true, snapshot, 1, skey); + + tuple = systable_getnext(scan); + + systable_endscan(scan); + table_close(rel, AccessShareLock); + + return HeapTupleIsValid(tuple); + } +} + /* * Return ObjectType for the given object type as given by * getObjectTypeDescription; if no valid ObjectType code exists, but it's a diff --git a/src/backend/catalog/pg_depend.c b/src/backend/catalog/pg_depend.c index 07c2d41c189..5618e3d26fa 100644 --- a/src/backend/catalog/pg_depend.c +++ b/src/backend/catalog/pg_depend.c @@ -33,8 +33,6 @@ #include "utils/syscache.h" -static bool isObjectPinned(const ObjectAddress *object); - /* * Record a dependency between 2 objects via their respective ObjectAddress. @@ -109,6 +107,12 @@ recordMultipleDependencies(const ObjectAddress *depender, if (isObjectPinned(referenced)) continue; + /* + * Acquire a lock and check object still exists while recording the + * dependency. + */ + LockNotPinnedObject(referenced); + if (slot_init_count < max_slots) { slot[slot_stored_count] = MakeSingleTupleTableSlot(RelationGetDescr(dependDesc), @@ -507,6 +511,12 @@ changeDependencyFor(Oid classId, Oid objectId, return 1; } + /* + * Acquire a lock and check object still exists while changing the + * dependency. + */ + LockNotPinnedObject(&objAddr); + depRel = table_open(DependRelationId, RowExclusiveLock); /* There should be existing dependency record(s), so search. */ @@ -707,7 +717,7 @@ changeDependenciesOn(Oid refClassId, Oid oldRefObjectId, * The passed subId, if any, is ignored; we assume that only whole objects * are pinned (and that this implies pinning their components). */ -static bool +bool isObjectPinned(const ObjectAddress *object) { return IsPinnedObject(object->classId, object->objectId); diff --git a/src/backend/utils/errcodes.txt b/src/backend/utils/errcodes.txt index 5b25402ebbe..58b498f68fc 100644 --- a/src/backend/utils/errcodes.txt +++ b/src/backend/utils/errcodes.txt @@ -278,6 +278,7 @@ Section: Class 2B - Dependent Privilege Descriptors Still Exist 2B000 E ERRCODE_DEPENDENT_PRIVILEGE_DESCRIPTORS_STILL_EXIST dependent_privilege_descriptors_still_exist 2BP01 E ERRCODE_DEPENDENT_OBJECTS_STILL_EXIST dependent_objects_still_exist +2BP02 E ERRCODE_DEPENDENT_OBJECTS_DOES_NOT_EXIST dependent_objects_does_not_exist Section: Class 2D - Invalid Transaction Termination diff --git a/src/include/catalog/dependency.h b/src/include/catalog/dependency.h index 2f3c1eae3c7..fa508ea70c6 100644 --- a/src/include/catalog/dependency.h +++ b/src/include/catalog/dependency.h @@ -101,6 +101,8 @@ typedef struct ObjectAddresses ObjectAddresses; /* in dependency.c */ extern void AcquireDeletionLock(const ObjectAddress *object, int flags); +extern void LockNotPinnedObject(const ObjectAddress *object); +extern bool isObjectPinned(const ObjectAddress *object); extern void ReleaseDeletionLock(const ObjectAddress *object); diff --git a/src/include/catalog/objectaddress.h b/src/include/catalog/objectaddress.h index 1f965e1faef..960b7e4bfa6 100644 --- a/src/include/catalog/objectaddress.h +++ b/src/include/catalog/objectaddress.h @@ -54,6 +54,7 @@ extern void check_object_ownership(Oid roleid, Node *object, Relation relation); extern Oid get_object_namespace(const ObjectAddress *address); +extern bool ObjectByIdExist(const ObjectAddress *address, bool use_snapshot_self); extern bool is_objectclass_supported(Oid class_id); extern const char *get_object_class_descr(Oid class_id); diff --git a/src/test/isolation/expected/test_dependencies_locks.out b/src/test/isolation/expected/test_dependencies_locks.out new file mode 100644 index 00000000000..820680f5e16 --- /dev/null +++ b/src/test/isolation/expected/test_dependencies_locks.out @@ -0,0 +1,129 @@ +Parsed test spec with 2 sessions + +starting permutation: s1_begin s1_create_function_in_schema s2_drop_schema s1_commit +step s1_begin: BEGIN; +step s1_create_function_in_schema: CREATE FUNCTION testschema.foo() RETURNS int AS 'select 1' LANGUAGE sql; +step s2_drop_schema: DROP SCHEMA testschema; +step s1_commit: COMMIT; +step s2_drop_schema: <... completed> +ERROR: cannot drop schema testschema because other objects depend on it + +starting permutation: s2_begin s2_drop_schema s1_create_function_in_schema s2_commit +step s2_begin: BEGIN; +step s2_drop_schema: DROP SCHEMA testschema; +step s1_create_function_in_schema: CREATE FUNCTION testschema.foo() RETURNS int AS 'select 1' LANGUAGE sql; +step s2_commit: COMMIT; +step s1_create_function_in_schema: <... completed> +ERROR: dependent object does not exist + +starting permutation: s1_begin s1_alter_function_schema s2_drop_alterschema s1_commit +step s1_begin: BEGIN; +step s1_alter_function_schema: ALTER FUNCTION public.falter() SET SCHEMA alterschema; +step s2_drop_alterschema: DROP SCHEMA alterschema; +step s1_commit: COMMIT; +step s2_drop_alterschema: <... completed> +ERROR: cannot drop schema alterschema because other objects depend on it + +starting permutation: s2_begin s2_drop_alterschema s1_alter_function_schema s2_commit +step s2_begin: BEGIN; +step s2_drop_alterschema: DROP SCHEMA alterschema; +step s1_alter_function_schema: ALTER FUNCTION public.falter() SET SCHEMA alterschema; +step s2_commit: COMMIT; +step s1_alter_function_schema: <... completed> +ERROR: dependent object does not exist + +starting permutation: s1_begin s1_create_function_with_argtype s2_drop_foo_type s1_commit +step s1_begin: BEGIN; +step s1_create_function_with_argtype: CREATE FUNCTION fooargtype(num foo) RETURNS int AS 'select 1' LANGUAGE sql; +step s2_drop_foo_type: DROP TYPE public.foo; +step s1_commit: COMMIT; +step s2_drop_foo_type: <... completed> +ERROR: cannot drop type foo because other objects depend on it + +starting permutation: s2_begin s2_drop_foo_type s1_create_function_with_argtype s2_commit +step s2_begin: BEGIN; +step s2_drop_foo_type: DROP TYPE public.foo; +step s1_create_function_with_argtype: CREATE FUNCTION fooargtype(num foo) RETURNS int AS 'select 1' LANGUAGE sql; +step s2_commit: COMMIT; +step s1_create_function_with_argtype: <... completed> +ERROR: dependent object does not exist + +starting permutation: s1_begin s1_create_function_with_rettype s2_drop_foo_rettype s1_commit +step s1_begin: BEGIN; +step s1_create_function_with_rettype: CREATE FUNCTION footrettype() RETURNS id LANGUAGE sql RETURN 1; +step s2_drop_foo_rettype: DROP DOMAIN id; +step s1_commit: COMMIT; +step s2_drop_foo_rettype: <... completed> +ERROR: cannot drop type id because other objects depend on it + +starting permutation: s2_begin s2_drop_foo_rettype s1_create_function_with_rettype s2_commit +step s2_begin: BEGIN; +step s2_drop_foo_rettype: DROP DOMAIN id; +step s1_create_function_with_rettype: CREATE FUNCTION footrettype() RETURNS id LANGUAGE sql RETURN 1; +step s2_commit: COMMIT; +step s1_create_function_with_rettype: <... completed> +ERROR: dependent object does not exist + +starting permutation: s1_begin s1_create_function_with_function s2_drop_function_f s1_commit +step s1_begin: BEGIN; +step s1_create_function_with_function: CREATE FUNCTION foofunc() RETURNS int LANGUAGE SQL RETURN f() + 1; +step s2_drop_function_f: DROP FUNCTION f(); +step s1_commit: COMMIT; +step s2_drop_function_f: <... completed> +ERROR: cannot drop function f() because other objects depend on it + +starting permutation: s2_begin s2_drop_function_f s1_create_function_with_function s2_commit +step s2_begin: BEGIN; +step s2_drop_function_f: DROP FUNCTION f(); +step s1_create_function_with_function: CREATE FUNCTION foofunc() RETURNS int LANGUAGE SQL RETURN f() + 1; +step s2_commit: COMMIT; +step s1_create_function_with_function: <... completed> +ERROR: dependent object does not exist + +starting permutation: s1_begin s1_create_domain_with_domain s2_drop_domain_id s1_commit +step s1_begin: BEGIN; +step s1_create_domain_with_domain: CREATE DOMAIN idid as id; +step s2_drop_domain_id: DROP DOMAIN id; +step s1_commit: COMMIT; +step s2_drop_domain_id: <... completed> +ERROR: cannot drop type id because other objects depend on it + +starting permutation: s2_begin s2_drop_domain_id s1_create_domain_with_domain s2_commit +step s2_begin: BEGIN; +step s2_drop_domain_id: DROP DOMAIN id; +step s1_create_domain_with_domain: CREATE DOMAIN idid as id; +step s2_commit: COMMIT; +step s1_create_domain_with_domain: <... completed> +ERROR: dependent object does not exist + +starting permutation: s1_begin s1_create_table_with_type s2_drop_footab_type s1_commit +step s1_begin: BEGIN; +step s1_create_table_with_type: CREATE TABLE tabtype(a footab); +step s2_drop_footab_type: DROP TYPE public.footab; +step s1_commit: COMMIT; +step s2_drop_footab_type: <... completed> +ERROR: cannot drop type footab because other objects depend on it + +starting permutation: s2_begin s2_drop_footab_type s1_create_table_with_type s2_commit +step s2_begin: BEGIN; +step s2_drop_footab_type: DROP TYPE public.footab; +step s1_create_table_with_type: CREATE TABLE tabtype(a footab); +step s2_commit: COMMIT; +step s1_create_table_with_type: <... completed> +ERROR: dependent object does not exist + +starting permutation: s1_begin s1_create_server_with_fdw_wrapper s2_drop_fdw_wrapper s1_commit +step s1_begin: BEGIN; +step s1_create_server_with_fdw_wrapper: CREATE SERVER srv_fdw_wrapper FOREIGN DATA WRAPPER fdw_wrapper; +step s2_drop_fdw_wrapper: DROP FOREIGN DATA WRAPPER fdw_wrapper RESTRICT; +step s1_commit: COMMIT; +step s2_drop_fdw_wrapper: <... completed> +ERROR: cannot drop foreign-data wrapper fdw_wrapper because other objects depend on it + +starting permutation: s2_begin s2_drop_fdw_wrapper s1_create_server_with_fdw_wrapper s2_commit +step s2_begin: BEGIN; +step s2_drop_fdw_wrapper: DROP FOREIGN DATA WRAPPER fdw_wrapper RESTRICT; +step s1_create_server_with_fdw_wrapper: CREATE SERVER srv_fdw_wrapper FOREIGN DATA WRAPPER fdw_wrapper; +step s2_commit: COMMIT; +step s1_create_server_with_fdw_wrapper: <... completed> +ERROR: dependent object does not exist diff --git a/src/test/isolation/isolation_schedule b/src/test/isolation/isolation_schedule index 1578ba191c8..83f626d51b5 100644 --- a/src/test/isolation/isolation_schedule +++ b/src/test/isolation/isolation_schedule @@ -126,3 +126,4 @@ test: serializable-parallel-3 test: matview-write-skew test: lock-nowait test: for-portion-of +test: test_dependencies_locks \ No newline at end of file diff --git a/src/test/isolation/specs/test_dependencies_locks.spec b/src/test/isolation/specs/test_dependencies_locks.spec new file mode 100644 index 00000000000..ee4130b2dc4 --- /dev/null +++ b/src/test/isolation/specs/test_dependencies_locks.spec @@ -0,0 +1,96 @@ +# Test that concurrent DDL properly prevents orphaned dependencies. +# +# When session 1 creates an object that depends on a referenced object, +# and session 2 concurrently drops that referenced object, the lock +# acquired during dependency recording must prevent the drop or the +# create must fail with "dependent object does not exist". + +setup +{ + CREATE SCHEMA testschema; + CREATE SCHEMA alterschema; + CREATE TYPE public.foo as enum ('one', 'two'); + CREATE TYPE public.footab as enum ('three', 'four'); + CREATE DOMAIN id AS int; + CREATE FUNCTION f() RETURNS int LANGUAGE SQL RETURN 1; + CREATE FUNCTION public.falter() RETURNS int LANGUAGE SQL RETURN 1; + CREATE FOREIGN DATA WRAPPER fdw_wrapper; +} + +teardown +{ + DROP FUNCTION IF EXISTS testschema.foo(); + DROP FUNCTION IF EXISTS fooargtype(num foo); + DROP FUNCTION IF EXISTS footrettype(); + DROP FUNCTION IF EXISTS foofunc(); + DROP FUNCTION IF EXISTS public.falter(); + DROP FUNCTION IF EXISTS alterschema.falter(); + DROP DOMAIN IF EXISTS idid; + DROP SERVER IF EXISTS srv_fdw_wrapper; + DROP TABLE IF EXISTS tabtype; + DROP SCHEMA IF EXISTS testschema; + DROP SCHEMA IF EXISTS alterschema; + DROP TYPE IF EXISTS public.foo; + DROP TYPE IF EXISTS public.footab; + DROP DOMAIN IF EXISTS id; + DROP FUNCTION IF EXISTS f(); + DROP FOREIGN DATA WRAPPER IF EXISTS fdw_wrapper; +} + +session "s1" + +step "s1_begin" { BEGIN; } +step "s1_create_function_in_schema" { CREATE FUNCTION testschema.foo() RETURNS int AS 'select 1' LANGUAGE sql; } +step "s1_create_function_with_argtype" { CREATE FUNCTION fooargtype(num foo) RETURNS int AS 'select 1' LANGUAGE sql; } +step "s1_create_function_with_rettype" { CREATE FUNCTION footrettype() RETURNS id LANGUAGE sql RETURN 1; } +step "s1_create_function_with_function" { CREATE FUNCTION foofunc() RETURNS int LANGUAGE SQL RETURN f() + 1; } +step "s1_alter_function_schema" { ALTER FUNCTION public.falter() SET SCHEMA alterschema; } +step "s1_create_domain_with_domain" { CREATE DOMAIN idid as id; } +step "s1_create_table_with_type" { CREATE TABLE tabtype(a footab); } +step "s1_create_server_with_fdw_wrapper" { CREATE SERVER srv_fdw_wrapper FOREIGN DATA WRAPPER fdw_wrapper; } +step "s1_commit" { COMMIT; } + +session "s2" + +step "s2_begin" { BEGIN; } +step "s2_drop_schema" { DROP SCHEMA testschema; } +step "s2_drop_alterschema" { DROP SCHEMA alterschema; } +step "s2_drop_foo_type" { DROP TYPE public.foo; } +step "s2_drop_foo_rettype" { DROP DOMAIN id; } +step "s2_drop_footab_type" { DROP TYPE public.footab; } +step "s2_drop_function_f" { DROP FUNCTION f(); } +step "s2_drop_domain_id" { DROP DOMAIN id; } +step "s2_drop_fdw_wrapper" { DROP FOREIGN DATA WRAPPER fdw_wrapper RESTRICT; } +step "s2_commit" { COMMIT; } + +# function - schema +permutation "s1_begin" "s1_create_function_in_schema" "s2_drop_schema" "s1_commit" +permutation "s2_begin" "s2_drop_schema" "s1_create_function_in_schema" "s2_commit" + +# alter function - schema +permutation "s1_begin" "s1_alter_function_schema" "s2_drop_alterschema" "s1_commit" +permutation "s2_begin" "s2_drop_alterschema" "s1_alter_function_schema" "s2_commit" + +# function - argtype +permutation "s1_begin" "s1_create_function_with_argtype" "s2_drop_foo_type" "s1_commit" +permutation "s2_begin" "s2_drop_foo_type" "s1_create_function_with_argtype" "s2_commit" + +# function - rettype +permutation "s1_begin" "s1_create_function_with_rettype" "s2_drop_foo_rettype" "s1_commit" +permutation "s2_begin" "s2_drop_foo_rettype" "s1_create_function_with_rettype" "s2_commit" + +# function - function +permutation "s1_begin" "s1_create_function_with_function" "s2_drop_function_f" "s1_commit" +permutation "s2_begin" "s2_drop_function_f" "s1_create_function_with_function" "s2_commit" + +# domain - domain +permutation "s1_begin" "s1_create_domain_with_domain" "s2_drop_domain_id" "s1_commit" +permutation "s2_begin" "s2_drop_domain_id" "s1_create_domain_with_domain" "s2_commit" + +# table - type +permutation "s1_begin" "s1_create_table_with_type" "s2_drop_footab_type" "s1_commit" +permutation "s2_begin" "s2_drop_footab_type" "s1_create_table_with_type" "s2_commit" + +# server - foreign data wrapper +permutation "s1_begin" "s1_create_server_with_fdw_wrapper" "s2_drop_fdw_wrapper" "s1_commit" +permutation "s2_begin" "s2_drop_fdw_wrapper" "s1_create_server_with_fdw_wrapper" "s2_commit" diff --git a/src/test/regress/expected/alter_table.out b/src/test/regress/expected/alter_table.out index 6dd22be0e8d..b891d68d4a7 100644 --- a/src/test/regress/expected/alter_table.out +++ b/src/test/regress/expected/alter_table.out @@ -2949,11 +2949,12 @@ begin; alter table alterlock2 add constraint alterlock2nv foreign key (f1) references alterlock (f1) NOT VALID; select * from my_locks order by 1; - relname | max_lockmode -------------+----------------------- - alterlock | ShareRowExclusiveLock - alterlock2 | ShareRowExclusiveLock -(2 rows) + relname | max_lockmode +----------------+----------------------- + alterlock | ShareRowExclusiveLock + alterlock2 | ShareRowExclusiveLock + alterlock_pkey | AccessShareLock +(3 rows) commit; begin; -- 2.34.1