我已在不同区域的三个 AWS 节点中安装了 2nd Quadrant PostgreSQL BDR 版本 1.0.2-2017-10-31- 以进行主动-主动复制。当我在一个节点的数据库中导入数据时，复制工作正常，它复制到另一个节点。
但是，在 BDR 组的数据库中发布任何 DDL 时，它会显示错误：
错误：数据库被另一个节点锁定到 ddl
提示：集群中的节点 (6489370455887834827,1,16387) 已经在执行 DDL
尽管没有应用程序指向数据库，也没有任何活动在其上执行。
请帮忙。
问候 Debasish
发生这种情况时，我发现留给我的唯一选择是通过运行以下命令从本地节点强制删除 BDR：
SELECT bdr.remove_bdr_from_local_node(true);
但是，如果这是一个支持 POSTGIS 的数据库，即使这样也会失败，并显示如下消息：
ERROR: cannot drop trigger truncate_trigger_19782 on table public.spatial_ref_sys because extension postgis requires it
HINT: You can drop extension postgis instead.
CONTEXT: SQL statement "DROP TRIGGER truncate_trigger_19782 ON public.spatial_ref_sys"
然后，您将尝试删除扩展 postgis ...
DROP EXTENSION postgis;
你会再次得到：
ERROR: database is locked against ddl by another node
HINT: Node (6489370455887834827,1,16387) in the cluster is already performing DDL
因此，如果您发现自己处于这种 catch-22 情况，请运行以下脚本。它将从本地节点中完全删除 BDR，允许您继续使用 DDL 命令。这当然会破坏复制，但之后您将能够以新名称重新加入节点。
不要忘记在第 4 行更改数据库的名称。
BEGIN;
SET LOCAL bdr.permit_unsafe_ddl_commands = true;
SET LOCAL bdr.skip_ddl_locking = true; --CHANGE DATABASE NAME BELOW
security label for 'bdr' on database changeme is '{"bdr": false}';
CREATE OR REPLACE FUNCTION bdr.remove_bdr_from_local_node(
force boolean DEFAULT false,
convert_global_sequences boolean DEFAULT true)
RETURNS void AS
$BODY$
DECLARE
local_node_status "char";
_seqschema name;
_seqname name;
_seqmax bigint;
_tableoid oid;
_truncate_tg record;
BEGIN
SELECT node_status FROM bdr.bdr_nodes WHERE (node_sysid, node_timeline, node_dboid) = bdr.bdr_get_local_nodeid()
INTO local_node_status;
IF NOT (local_node_status = 'k' OR local_node_status IS NULL) THEN
IF force THEN
RAISE WARNING 'forcing deletion of possibly active BDR node';
UPDATE bdr.bdr_nodes
SET node_status = 'k'
WHERE (node_sysid, node_timeline, node_dboid) = bdr.bdr_get_local_nodeid();
PERFORM bdr._test_pause_worker_management(false);
PERFORM pg_sleep(5);
RAISE NOTICE 'node forced to parted state, now removing';
ELSE
RAISE EXCEPTION 'this BDR node might still be active, not removing';
END IF;
END IF;
RAISE NOTICE 'removing BDR from node';
-- Alter all global sequences to become local sequences. That alone won't
-- they're in the right position, since another node might've had numerically
-- higher global sequence values. So we need to then move it up to the
-- highest allocated chunk for any node and setval to it.
IF convert_global_sequences THEN
FOR _seqschema, _seqname, _seqmax IN
SELECT
n.nspname,
c.relname,
(
SELECT max(upper(seqrange))
FROM bdr.bdr_sequence_values
WHERE seqschema = n.nspname
AND seqname = c.relname
AND in_use
) AS seqmax
FROM pg_class c
INNER JOIN pg_namespace n ON (c.relnamespace = n.oid)
WHERE c.relkind = 'S'
AND c.relam = (SELECT s.oid FROM pg_seqam s WHERE s.seqamname = 'bdr')
LOOP
EXECUTE format('ALTER SEQUENCE %I.%I USING local;', _seqschema, _seqname);
-- This shouldn't be necessary, see bug #215
IF _seqmax IS NOT NULL THEN
EXECUTE format('SELECT setval(%L, $1)', quote_ident(_seqschema)||'.'||quote_ident(_seqname)) USING (_seqmax);
END IF;
END LOOP;
ELSE
RAISE NOTICE 'global sequences not converted to local; they will not work until a new nodegroup is created';
END IF;
-- Strip the database security label
EXECUTE format('SECURITY LABEL FOR bdr ON DATABASE %I IS NULL', current_database());
-- Suspend worker management, so when we terminate apply workers and
-- walsenders they won't get relaunched.
PERFORM bdr._test_pause_worker_management(true);
-- Terminate every worker associated with this DB
PERFORM bdr.terminate_walsender_workers(node_sysid, node_timeline, node_dboid)
FROM bdr.bdr_nodes
WHERE (node_sysid, node_timeline, node_dboid) <> bdr.bdr_get_local_nodeid();
PERFORM bdr.terminate_apply_workers(node_sysid, node_timeline, node_dboid)
FROM bdr.bdr_nodes
WHERE (node_sysid, node_timeline, node_dboid) <> bdr.bdr_get_local_nodeid();
-- Delete all connections and all nodes except the current one
DELETE FROM bdr.bdr_connections
WHERE (conn_sysid, conn_timeline, conn_dboid) <> bdr.bdr_get_local_nodeid();
DELETE FROM bdr.bdr_nodes
WHERE (node_sysid, node_timeline, node_dboid) <> bdr.bdr_get_local_nodeid();
-- Let the perdb worker resume work and figure out everything's
-- going away.
PERFORM bdr._test_pause_worker_management(false);
PERFORM bdr.bdr_connections_changed();
-- Give it a few seconds
PERFORM pg_sleep(2);
-- Shut down the perdb worker
PERFORM pg_terminate_backend(pid)
FROM pg_stat_activity, bdr.bdr_get_local_nodeid() ni
WHERE datname = current_database()
AND application_name = format('bdr: (%s,%s,%s,): perdb', ni.sysid, ni.timeline, ni.dboid);
-- Clear out the rest of bdr_nodes and bdr_connections
DELETE FROM bdr.bdr_nodes;
DELETE FROM bdr.bdr_connections;
-- Drop peer replication slots for this DB
PERFORM pg_drop_replication_slot(slot_name)
FROM pg_catalog.pg_replication_slots,
bdr.bdr_parse_slot_name(slot_name) ps
WHERE ps.local_dboid = (select oid from pg_database where datname = current_database())
AND plugin = 'bdr';
-- and replication identifiers
PERFORM pg_replication_identifier_drop(riname)
FROM pg_catalog.pg_replication_identifier,
bdr.bdr_parse_replident_name(riname) pi
WHERE pi.local_dboid = (select oid from pg_database where datname = current_database());
-- Strip the security labels we use for replication sets from all the tables
FOR _tableoid IN
SELECT objoid
FROM pg_catalog.pg_seclabel
INNER JOIN pg_catalog.pg_class ON (pg_seclabel.objoid = pg_class.oid)
WHERE provider = 'bdr'
AND classoid = 'pg_catalog.pg_class'::regclass
AND pg_class.relkind = 'r'
LOOP
-- regclass's text out adds quoting and schema qualification if needed
EXECUTE format('SECURITY LABEL FOR bdr ON TABLE %s IS NULL', _tableoid::regclass);
END LOOP;
-- Drop the on-truncate triggers. They'd otherwise get cascade-dropped
-- when the BDR extension was dropped, but this way the system is clean. We
-- can't drop ones under the 'bdr' schema.
FOR _truncate_tg IN
SELECT
n.nspname AS tgrelnsp,
c.relname AS tgrelname,
t.tgname AS tgname,
d.objid AS tgobjid,
d.refobjid AS tgrelid
FROM pg_depend d
INNER JOIN pg_class c ON (d.refclassid = 'pg_class'::regclass AND d.refobjid = c.oid)
INNER JOIN pg_namespace n ON (c.relnamespace = n.oid)
INNER JOIN pg_trigger t ON (d.classid = 'pg_trigger'::regclass and d.objid = t.oid)
INNER JOIN pg_depend d2 ON (d.classid = d2.classid AND d.objid = d2.objid)
WHERE tgname LIKE 'truncate_trigger_%'
AND d2.refclassid = 'pg_proc'::regclass
AND d2.refobjid = 'bdr.queue_truncate'::regproc
AND n.nspname <> 'bdr'
LOOP
-- THIS IS THE PROBLEMATIC AREA FOR POSTGIS
/*EXECUTE format('DROP TRIGGER %I ON %I.%I',
_truncate_tg.tgname, _truncate_tg.tgrelnsp, _truncate_tg.tgrelname);*/
-- END OF PROBLEMATIC AREA
-- The trigger' dependency entry will be dangling because of how we
-- dropped it
DELETE FROM pg_depend
WHERE classid = 'pg_trigger'::regclass
AND objid = _truncate_tg.tgobjid
AND (refclassid = 'pg_proc'::regclass AND refobjid = 'bdr.queue_truncate'::regproc)
OR
(refclassid = 'pg_class'::regclass AND refobjid = _truncate_tg.tgrelid);
END LOOP;
-- Delete the other detritus from the extension. The user should really drop it,
-- but we should try to restore a clean state anyway.
DELETE FROM bdr.bdr_queued_commands;
DELETE FROM bdr.bdr_queued_drops;
DELETE FROM bdr.bdr_global_locks;
DELETE FROM bdr.bdr_conflict_handlers;
DELETE FROM bdr.bdr_conflict_history;
DELETE FROM bdr.bdr_replication_set_config;
DELETE FROM bdr.bdr_sequence_elections;
DELETE FROM bdr.bdr_sequence_values;
DELETE FROM bdr.bdr_votes;
-- We can't drop the BDR extension, we just need to tell the
-- user to do that.
RAISE NOTICE 'BDR removed from this node. You can now DROP EXTENSION bdr and, if this is the last BDR node on this PostgreSQL instance, remove bdr from shared_preload_libraries.';
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
ALTER FUNCTION bdr.remove_bdr_from_local_node(boolean, boolean) SET bdr.skip_ddl_locking='on';
ALTER FUNCTION bdr.remove_bdr_from_local_node(boolean, boolean) SET bdr.permit_unsafe_ddl_commands='on';
ALTER FUNCTION bdr.remove_bdr_from_local_node(boolean, boolean) SET bdr.skip_ddl_replication='on';
ALTER FUNCTION bdr.remove_bdr_from_local_node(boolean, boolean) SET search_path="bdr,pg_catalog";
ALTER FUNCTION bdr.remove_bdr_from_local_node(boolean, boolean)
OWNER TO postgres;
GRANT EXECUTE ON FUNCTION bdr.remove_bdr_from_local_node(boolean, boolean) TO postgres;
REVOKE ALL ON FUNCTION bdr.remove_bdr_from_local_node(boolean, boolean) FROM public;
COMMENT ON FUNCTION bdr.remove_bdr_from_local_node(boolean, boolean) IS 'Remove all BDR security labels, slots, replication origins, replication sets, etc from the local node, and turn all global sequences into local sequences';
SELECT bdr.remove_bdr_from_local_node(true);
COMMIT;