DDL Command handling matrix =========================== The following table describes the utility or DDL commands that are allowed, the ones that are replicated, and the type of global lock they take when they’re replicated. For some more complex statements like ``ALTER TABLE`` , these can differ depending on the subcommands executed. Every such command has detailed explanation under the following table. Command matrix -------------- .. csv-table:: :header: Command,Allowed,Replicated,Lock :widths: 15,5,5,10 :align: left :class: longtable ALTER AGGREGATE,Y,Y,DDL ALTER CAST,Y,Y,DDL ALTER COLLATION,Y,Y,DDL ALTER CONVERSION,Y,Y,DDL ALTER DATABASE,Y,N,N ALTER DATABASE LINK,Y,Y,DDL ALTER DEFAULT PRIVILEGES,Y,Y,DDL ALTER DIRECTORY,Y,Y,DDL ALTER DOMAIN,Y,Y,DDL ALTER EVENT TRIGGER,Y,Y,DDL ALTER EXTENSION,Y,Y,DDL ALTER FOREIGN DATA WRAPPER,Y,Y,DDL ALTER FOREIGN TABLE,Y,Y,DDL ALTER FUNCTION,Y,Y,DDL ALTER INDEX,Y,Y,DDL ALTER LANGUAGE,Y,Y,DDL ALTER LARGE OBJECT,N,N,N ALTER MATERIALIZED VIEW,Y,N,N ALTER OPERATOR,Y,Y,DDL ALTER OPERATOR CLASS,Y,Y,DDL ALTER OPERATOR FAMILY,Y,Y,DDL ALTER PACKAGE,Y,Y,DDL ALTER POLICY,Y,Y,DDL ALTER PROCEDURE,Y,Y,DDL ALTER PROFILE,Y,Y,:ref:`Architecture details` ALTER PUBLICATION,Y,Y,DDL ALTER QUEUE,Y,Y,DDL ALTER QUEUE TABLE,Y,Y,DDL ALTER REDACTION POLICY,Y,Y,DDL ALTER RESOURCE GROUP,Y,N,N ALTER ROLE,Y,Y,DDL ALTER ROUTINE,Y,Y,DDL ALTER RULE,Y,Y,DDL ALTER SCHEMA,Y,Y,DDL ALTER SEQUENCE,:ref:`Architecture details` ,Y,DML ALTER SERVER,Y,Y,DDL ALTER SESSION,Y,N,N ALTER STATISTICS,Y,Y,DDL ALTER SUBSCRIPTION,Y,Y,DDL ALTER SYNONYM,Y,Y,DDL ALTER SYSTEM,Y,N,N ALTER TABLE,:ref:`Architecture details` ,Y,:ref:`Architecture details` ALTER TABLESPACE,Y,N,N ALTER TEXT SEARCH CONFIGURATION,Y,Y,DDL ALTER TEXT SEARCH DICTIONARY,Y,Y,DDL ALTER TEXT SEARCH PARSER,Y,Y,DDL ALTER TEXT SEARCH TEMPLATE,Y,Y,DDL ALTER TRIGGER,Y,Y,DDL ALTER TYPE,Y,Y,DDL ALTER USER MAPPING,Y,Y,DDL ALTER VIEW,Y,Y,DDL ANALYZE,Y,N,N BEGIN,Y,N,N CHECKPOINT,Y,N,N CLOSE,Y,N,N CLOSE CURSOR,Y,N,N CLOSE CURSOR ALL,Y,N,N CLUSTER,Y,N,N COMMENT,Y,:ref:`Architecture details` ,DDL COMMIT,Y,N,N COMMIT PREPARED,Y,N,N COPY,Y,N,N COPY FROM,Y,N,N CREATE ACCESS METHOD,Y,Y,DDL CREATE AGGREGATE,Y,Y,DDL CREATE CAST,Y,Y,DDL CREATE COLLATION,Y,Y,DDL CREATE CONSTRAINT,Y,Y,DDL CREATE CONVERSION,Y,Y,DDL CREATE DATABASE,Y,N,N CREATE DATABASE LINK,Y,Y,DDL CREATE DIRECTORY,Y,Y,DDL CREATE DOMAIN,Y,Y,DDL CREATE EVENT TRIGGER,Y,Y,DDL CREATE EXTENSION,Y,Y,DDL CREATE FOREIGN DATA WRAPPER,Y,Y,DDL CREATE FOREIGN TABLE,Y,Y,DDL CREATE FUNCTION,Y,Y,DDL CREATE INDEX,Y,Y,DML CREATE LANGUAGE,Y,Y,DDL CREATE MATERIALIZED VIEW,Y,N,N CREATE OPERATOR,Y,Y,DDL CREATE OPERATOR CLASS,Y,Y,DDL CREATE OPERATOR FAMILY,Y,Y,DDL CREATE PACKAGE,Y,Y,DDL CREATE PACKAGE BODY,Y,Y,DDL CREATE POLICY,Y,Y,DML CREATE PROCEDURE,Y,Y,DDL CREATE PROFILE,Y,Y,:ref:`Architecture details` CREATE PUBLICATION,Y,Y,DDL CREATE QUEUE,Y,Y,DDL CREATE QUEUE TABLE,Y,Y,DDL CREATE REDACTION POLICY,Y,Y,DDL CREATE RESOURCE GROUP,Y,N,N CREATE ROLE,Y,Y,DDL CREATE ROUTINE,Y,Y,DDL CREATE RULE,Y,Y,DDL CREATE SCHEMA,Y,Y,DDL CREATE SEQUENCE,:ref:`Architecture details` ,Y,DDL CREATE SERVER,Y,Y,DDL CREATE STATISTICS,Y,Y,DDL CREATE SUBSCRIPTION,Y,Y,DDL CREATE SYNONYM,Y,Y,DDL CREATE TABLE,:ref:`Architecture details` ,Y,DDL CREATE TABLE AS,:ref:`Architecture details` ,Y,DDL CREATE TABLESPACE,Y,N,N CREATE TEXT SEARCH CONFIGURATION,Y,Y,DDL CREATE TEXT SEARCH DICTIONARY,Y,Y,DDL CREATE TEXT SEARCH PARSER,Y,Y,DDL CREATE TEXT SEARCH TEMPLATE,Y,Y,DDL CREATE TRANSFORM,Y,Y,DDL CREATE TRIGGER,Y,Y,DDL CREATE TYPE,Y,Y,DDL CREATE TYPE BODY,Y,Y,DDL CREATE USER MAPPING,Y,Y,DDL CREATE VIEW,Y,Y,DDL DEALLOCATE,Y,N,N DEALLOCATE ALL,Y,N,N DECLARE CURSOR,Y,N,N DISCARD,Y,N,N DISCARD ALL,Y,N,N DISCARD PLANS,Y,N,N DISCARD SEQUENCES,Y,N,N DISCARD TEMP,Y,N,N DO,Y,N,N DROP ACCESS METHOD,Y,Y,DDL DROP AGGREGATE,Y,Y,DDL DROP CAST,Y,Y,DDL DROP COLLATION,Y,Y,DDL DROP CONSTRAINT,Y,Y,DDL DROP CONVERSION,Y,Y,DDL DROP DATABASE,Y,N,N DROP DATABASE LINK,Y,Y,DDL DROP DIRECTORY,Y,Y,DDL DROP DOMAIN,Y,Y,DDL DROP EVENT TRIGGER,Y,Y,DDL DROP EXTENSION,Y,Y,DDL DROP FOREIGN DATA WRAPPER,Y,Y,DDL DROP FOREIGN TABLE,Y,Y,DDL DROP FUNCTION,Y,Y,DDL DROP INDEX,Y,Y,DDL DROP LANGUAGE,Y,Y,DDL DROP MATERIALIZED VIEW,Y,N,N DROP OPERATOR,Y,Y,DDL DROP OPERATOR CLASS,Y,Y,DDL DROP OPERATOR FAMILY,Y,Y,DDL DROP OWNED,Y,Y,DDL DROP PACKAGE,Y,Y,DDL DROP PACKAGE BODY,Y,Y,DDL DROP POLICY,Y,Y,DDL DROP PROCEDURE,Y,Y,DDL DROP PROFILE,Y,Y,DDL DROP PUBLICATION,Y,Y,DDL DROP QUEUE,Y,Y,DDL DROP QUEUE TABLE,Y,Y,DDL DROP REDACTION POLICY,Y,Y,DDL DROP RESOURCE GROUP,Y,N,N DROP ROLE,Y,Y,DDL DROP ROUTINE,Y,Y,DDL DROP RULE,Y,Y,DDL DROP SCHEMA,Y,Y,DDL DROP SEQUENCE,Y,Y,DDL DROP SERVER,Y,Y,DDL DROP STATISTICS,Y,Y,DDL DROP SUBSCRIPTION,Y,Y,DDL DROP SYNONYM,Y,Y,DDL DROP TABLE,Y,Y,DML DROP TABLESPACE,Y,N,N DROP TEXT SEARCH CONFIGURATION,Y,Y,DDL DROP TEXT SEARCH DICTIONARY,Y,Y,DDL DROP TEXT SEARCH PARSER,Y,Y,DDL DROP TEXT SEARCH TEMPLATE,Y,Y,DDL DROP TRANSFORM,Y,Y,DDL DROP TRIGGER,Y,Y,DDL DROP TYPE,Y,Y,DDL DROP TYPE BODY,Y,Y,DDL DROP USER MAPPING,Y,Y,DDL DROP VIEW,Y,Y,DDL EXECUTE,Y,N,N EXPLAIN,Y,:ref:`Architecture details` ,:ref:`Architecture details` FETCH,Y,N,N GRANT,Y,:ref:`Architecture details` ,DDL GRANT ROLE,Y,Y,DDL IMPORT FOREIGN SCHEMA,Y,Y,DDL LISTEN,Y,N,N LOAD,Y,N,N LOAD ROW DATA,Y,Y,DDL LOCK TABLE,Y,N,:ref:`Architecture details` MOVE,Y,N,N NOTIFY,Y,N,N PREPARE,Y,N,N PREPARE TRANSACTION,Y,N,N REASSIGN OWNED,Y,Y,DDL REFRESH MATERIALIZED VIEW,Y,N,N REINDEX,Y,N,N RELEASE,Y,N,N RESET,Y,N,N REVOKE,Y,:ref:`Architecture details` ,DDL REVOKE ROLE,Y,Y,DDL ROLLBACK,Y,N,N ROLLBACK PREPARED,Y,N,N SAVEPOINT,Y,N,N SECURITY LABEL,Y,:ref:`Architecture details` ,DDL SELECT INTO,:ref:`Architecture details` ,Y,DDL SET,Y,N,N SET CONSTRAINTS,Y,N,N SHOW,Y,N,N START TRANSACTION,Y,N,N TRUNCATE TABLE,Y,:ref:`Architecture details` ,:ref:`Architecture details` UNLISTEN,Y,N,N VACUUM,Y,N,N Command Notes ------------- .. container:: :name: bdr_ddl_allowed_AlterSeqStmt ALTER SEQUENCE ^^^^^^^^^^^^^^ Generally ``ALTER SEQUENCE`` is supported, but when using global sequences, some options have no effect. ``ALTER SEQUENCE ... RENAME`` isn’t supported on galloc sequences (only). ``ALTER SEQUENCE ... SET SCHEMA`` isn’t supported on galloc sequences (only). ALTER TABLE ^^^^^^^^^^^ Generally, ``ALTER TABLE`` commands are allowed. However, several subcommands aren’t supported. .. container:: :name: bdr_ddl_allowed_AlterTableStmt ALTER TABLE disallowed commands ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Some variants of ``ALTER TABLE`` currently aren’t allowed on a PGD node: - ``ADD COLUMN ... DEFAULT (non-immutable expression)`` — This is not allowed because it currently results in different data on different nodes. See :ref:`Adding a column ` for a suggested workaround. - ``ADD CONSTRAINT ... EXCLUDE`` — Exclusion constraints are not supported. Exclusion constraints are a way to ensure that no two rows in a table have overlapping ranges. This is useful in a synchronous system where you can ensure that the constraint is enforced on all nodes at the same time. But in an asynchronous system, you can’t ensure that the constraint is enforced on all nodes at the same time. This can lead to data inconsistency and changes that can’t be replayed; therefore, exclusion constraints aren’t supported. - ``ALTER TABLE ... SET WITH[OUT] OIDS`` — Isn’t supported for the same reasons as in ``CREATE TABLE`` . - ``ALTER COLUMN ... SET STORAGE external`` — Is rejected if the column is one of the columns of the replica identity for the table. - ``RENAME`` — Can’t rename an Autopartitioned table. - ``SET SCHEMA`` — Can’t set the schema of an Autopartitioned table. - ``ALTER COLUMN ... TYPE`` — Changing a column’s type isn’t supported if the command causes the whole table to be rewritten, which occurs when the change isn’t binary coercible. Binary coercible changes might be allowed only one way. For example, the change from ``VARCHAR(128)`` to ``VARCHAR(256)`` is binary coercible and therefore allowed, whereas the change ``VARCHAR(256)`` to ``VARCHAR(128)`` isn’t binary coercible and therefore normally disallowed. Nonreplicated ``ALTER COLUMN ... TYPE`` , can be allowed if the column is automatically castable to the new type (it doesn’t contain the ``USING`` clause). An example follows. Table rewrites hold an AccessExclusiveLock for extended periods on larger tables, so such commands are likely to be infeasible on highly available databases in any case. See :ref:`Changing a column's type ` for a suggested workaround. - ``ALTER TABLE ... ADD FOREIGN KEY`` — Isn’t supported if current user doesn’t have permission to read the referenced table or if the referenced table has RLS restrictions enabled that the current user can’t bypass. The following example fails because it tries to add a constant value of type ``timestamp`` onto a column of type ``timestamptz`` . The cast between ``timestamp`` and ``timestamptz`` relies on the time zone of the session and so isn’t immutable. .. code:: sql ALTER TABLE foo ADD expiry_date timestamptz DEFAULT timestamp 2100-01-01 00:00:00 NOT NULL; Starting in PGD 3.7.4, you can add certain types of constraints, such as ``CHECK`` and ``FOREIGN KEY`` constraints, without taking a DML lock. But this requires a two-step process of first creating a ``NOT VALID`` constraint and then validating the constraint in a separate transaction with the ``ALTER TABLE ... VALIDATE CONSTRAINT`` command. See :ref:`Adding a CONSTRAINT ` for more details. .. container:: :name: bdr_ddl_lock_relation_AlterTableStmt ALTER TABLE locking ^^^^^^^^^^^^^^^^^^^ The following variants of ``ALTER TABLE`` take only DDL lock and not a DML lock: - ``ALTER TABLE ... ADD COLUMN ... (immutable) DEFAULT`` - ``ALTER TABLE ... ALTER COLUMN ... SET DEFAULT expression`` - ``ALTER TABLE ... ALTER COLUMN ... DROP DEFAULT`` - ``ALTER TABLE ... ALTER COLUMN ... TYPE`` if it doesn’t require rewrite - ``ALTER TABLE ... ALTER COLUMN ... SET STATISTICS`` - ``ALTER TABLE ... VALIDATE CONSTRAINT`` - ``ALTER TABLE ... ATTACH PARTITION`` - ``ALTER TABLE ... DETACH PARTITION`` - ``ALTER TABLE ... ENABLE TRIGGER`` (``ENABLE REPLICA TRIGGER`` still takes a DML lock) - ``ALTER TABLE ... CLUSTER ON`` - ``ALTER TABLE ... SET WITHOUT CLUSTER`` - ``ALTER TABLE ... SET ( storage_parameter = value [, ... ] )`` - ``ALTER TABLE ... RESET ( storage_parameter = [, ... ] )`` - ``ALTER TABLE ... OWNER TO`` All other variants of ``ALTER TABLE`` take a DML lock on the table being modified. Some variants of ``ALTER TABLE`` have restrictions, noted below. ALTER TABLE examples ^^^^^^^^^^^^^^^^^^^^ This next example works because the type change is binary coercible and so doesn’t cause a table rewrite. It executes as a catalog-only change. .. code:: sql CREATE TABLE foo (id BIGINT PRIMARY KEY, description VARCHAR(20)); ALTER TABLE foo ALTER COLUMN description TYPE VARCHAR(128); However, making this change to reverse the command isn’t possible because the change from ``VARCHAR(128)`` to ``VARCHAR(20)`` isn’t binary coercible. .. code:: sql ALTER TABLE foo ALTER COLUMN description TYPE VARCHAR(20); For workarounds, see :ref:`Restricted DDL workarounds ` . It’s useful to provide context for different types of ``ALTER TABLE ... ALTER COLUMN TYPE`` (ATCT) operations that are possible in general and in nonreplicated environments. Some ATCT operations update only the metadata of the underlying column type and don’t require a rewrite of the underlying table data. This is typically the case when the existing column type and the target type are binary coercible. For example: .. code:: sql CREATE TABLE sample (col1 BIGINT PRIMARY KEY, col2 VARCHAR(128), col3 INT); ALTER TABLE sample ALTER COLUMN col2 TYPE VARCHAR(256); You can also change the column type to ``VARCHAR`` or ``TEXT`` data types because of binary coercibility. Again, this is just a metadata update of the underlying column type. .. code:: sql ALTER TABLE sample ALTER COLUMN col2 TYPE VARCHAR; ALTER TABLE sample ALTER COLUMN col2 TYPE TEXT; However, if you want to reduce the size of col2, then that leads to a rewrite of the underlying table data. Rewrite of a table is normally restricted. .. code:: sql ALTER TABLE sample ALTER COLUMN col2 TYPE VARCHAR(64); ERROR: ALTER TABLE ... ALTER COLUMN TYPE that rewrites table data may not affect replicated tables on a PGD node To give an example with nontext types, consider col3 above with type INTEGER. An ATCT operation that tries to convert to SMALLINT or BIGINT fails in a similar manner as above. .. code:: sql ALTER TABLE sample ALTER COLUMN col3 TYPE bigint; ERROR: ALTER TABLE ... ALTER COLUMN TYPE that rewrites table data may not affect replicated tables on a PGD node In both of these failing cases, there’s an automatic assignment cast from the current types to the target types. However, there’s no binary coercibility, which ends up causing a rewrite of the underlying table data. In such cases, in controlled DBA environments, you can change the type of a column to an automatically castable one by adopting a rolling upgrade for the type of this column in a nonreplicated environment on all the nodes, one by one. Suppose the DDL isn’t replicated and the change of the column type is to an automatically castable one. You can then allow the rewrite locally on the node performing the alter, along with concurrent activity on other nodes on this same table. You can then repeat this nonreplicated ATCT operation on all the nodes one by one to bring about the desired change of the column type across the entire EDB Postgres Distributed cluster. Because this involves a rewrite, the activity still takes the DML lock for a brief period and thus requires that the whole cluster is available. With these specifics in place, you can carry out the rolling upgrade of the nonreplicated alter activity like this: .. code:: sql - - foreach node in EDB Postgres Distributed cluster do: SET bdr.ddl_replication TO FALSE; ALTER TABLE sample ALTER COLUMN col2 TYPE VARCHAR(64); ALTER TABLE sample ALTER COLUMN col3 TYPE BIGINT; RESET bdr.ddl_replication; - - done Due to automatic assignment casts being available for many data types, this local nonreplicated ATCT operation supports a wide variety of conversions. Also, ATCT operations that use a ``USING`` clause are likely to fail because of the lack of automatic assignment casts. This example shows a few common conversions with automatic assignment casts: .. code:: sql - - foreach node in EDB Postgres Distributed cluster do: SET bdr.ddl_replication TO FALSE; ATCT operations to-from {INTEGER, SMALLINT, BIGINT} ATCT operations to-from {CHAR(n), VARCHAR(n), VARCHAR, TEXT} ATCT operations from numeric types to text types RESET bdr.ddl_replication; - - done This example isn’t an exhaustive list of possibly allowable ATCT operations in a nonreplicated environment. Not all ATCT operations work. The cases where no automatic assignment is possible fail even if you disable DDL replication. So, while conversion from numeric types to text types works in a nonreplicated environment, conversion back from text type to numeric types fails. .. code:: sql SET bdr.ddl_replication TO FALSE; - - conversion from BIGINT to TEXT works ALTER TABLE sample ALTER COLUMN col3 TYPE TEXT; - - conversion from TEXT back to BIGINT fails ALTER TABLE sample ALTER COLUMN col3 TYPE BIGINT; ERROR: ALTER TABLE ... ALTER COLUMN TYPE which cannot be automatically cast to new type may not affect replicated tables on a PGD node RESET bdr.ddl_replication; While the ATCT operations in nonreplicated environments support a variety of type conversions, the rewrite can still fail if the underlying table data contains values that you can’t assign to the new data type. For example, suppose the current type for a column is ``VARCHAR(256)`` and you try a nonreplicated ATCT operation to convert it into ``VARCHAR(128)`` . If there’s any existing data in the table that’s wider than 128 bytes, then the rewrite operation fails locally. .. code:: sql INSERT INTO sample VALUES (1, repeat(a, 200), 10); SET bdr.ddl_replication TO FALSE; ALTER TABLE sample ALTER COLUMN col2 TYPE VARCHAR(128); INFO: in rewrite ERROR: value too long for type character varying(128) If underlying table data meets the characteristics of the new type, then the rewrite succeeds. However, replication might fail if other nodes that haven’t yet performed the nonreplicated rolling data type upgrade introduce new data that is wider than 128 bytes concurrently to this local ATCT operation. This brings replication to a halt in the cluster. So be aware of the data type restrictions and characteristics at the database and application levels while performing these nonreplicated rolling data type upgrade operations. We strongly recommend that you perform and test such ATCT operations in controlled and fully aware DBA environments. These ATCT operations are asymmetric, and backing out certain changes that fail can lead to table rewrites that take a long time. Also, you can’t perform the implicit castable ALTER activity in transaction blocks. ALTER TYPE ^^^^^^^^^^ ``ALTER TYPE`` is replicated, but a global DML lock isn’t applied to all tables that use that data type, since PostgreSQL doesn’t record those dependencies. See :ref:`Restricted DDL workarounds ` . .. container:: :name: bdr_ddl_can_replicate_comment COMMENT ON ^^^^^^^^^^ All variants of ``COMMENT ON`` are allowed, but ``COMMENT ON TABLESPACE/DATABASE/LARGE OBJECT`` isn’t replicated. .. container:: :name: bdr_ddl_allowed_CreateSeqStmt CREATE PROFILE or ALTER PROFILE ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The ``PASSWORD_VERIFY_FUNCTION`` associated with the profile should be ``IMMUTABLE`` if the function is ``SECURITY DEFINER`` . Such a ``CREATE PROFILE`` or ``ALTER PROFILE`` command will be replicated but subsequent ``CREATE USER`` or ``ALTER USER`` commands using this profile will break the replication due to the ``writer`` worker throwing the error: ``cannot change current role within security-restricted operation`` . .. container:: :name: bdr_ddl_allowed_CreateAlterProfile CREATE SEQUENCE ^^^^^^^^^^^^^^^ Generally ``CREATE SEQUENCE`` is supported, but when using global sequences, some options have no effect. .. container:: :name: bdr_ddl_allowed_CreateStmt CREATE TABLE ^^^^^^^^^^^^ Generally ``CREATE TABLE`` is supported, but ``CREATE TABLE WITH OIDS`` isn’t allowed on a PGD node. .. container:: :name: bdr_ddl_allowed_CreateTableAsStmt CREATE TABLE AS and SELECT INTO ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ``CREATE TABLE AS`` and ``SELECT INTO`` are allowed only if all subcommands are also allowed. EXPLAIN ^^^^^^^ Generally ``EXPLAIN`` is allowed, but because ``EXPLAIN ANALYZE`` can have side effects on the database, there are some restrictions on it. .. container:: :name: bdr_ddl_can_replicate_explain EXPLAIN ANALYZE Replication ^^^^^^^^^^^^^^^^^^^^^^^^^^^ ``EXPLAIN ANALYZE`` follows replication rules of the analyzed statement. .. container:: :name: bdr_ddl_lock_explain_stmt EXPLAIN ANALYZE Locking ^^^^^^^^^^^^^^^^^^^^^^^ ``EXPLAIN ANALYZE`` follows locking rules of the analyzed statement. .. container:: :name: bdr_ddl_can_replicate_grant GRANT and REVOKE ^^^^^^^^^^^^^^^^ Generally ``GRANT`` and ``REVOKE`` statements are supported, however ``GRANT/REVOKE ON TABLESPACE/LARGE OBJECT`` aren’t replicated. .. container:: :name: bdr_ddl_lock_lock_stmt LOCK TABLE ^^^^^^^^^^ LOCK TABLE isn’t replicated, but it might acquire the global DML lock when ``bdr.lock_table_locking`` is set ``on`` . You can also use The ``bdr.global_lock_table()`` function to explicitly request a global DML lock. .. container:: :name: bdr_ddl_can_replicate_seclabel SECURITY LABEL ^^^^^^^^^^^^^^ All variants of ``SECURITY LABEL`` are allowed, but ``SECURITY LABEL ON TABLESPACE/DATABASE/LARGE OBJECT`` isn’t replicated. .. container:: :name: bdr_ddl_can_replicate_truncate TRUNCATE Replication ^^^^^^^^^^^^^^^^^^^^ ``TRUNCATE`` command is replicated as DML, not as a DDL statement. Whether the ``TRUNCATE`` on table is replicated depends on replication settings for each affected table. .. container:: :name: bdr_ddl_lock_truncate_stmt TRUNCATE Locking ^^^^^^^^^^^^^^^^ Even though ``TRUNCATE`` isn’t replicated the same way as other DDL, it can acquire the global DML lock when ``bdr.truncate_locking`` is set to ``on`` .