最近遇到truncate表，无法清理的情况，在master节点查看加锁情况，并未加锁
这种情况极有可能是segment节点相关表加了锁，所以遇到这种情况除了排查master节点的锁，
所有的segment也要查看锁的持有情况，然后根据情况，进行处理。
master节点：
查看segment锁情况
select gp_execution_dbid(), pid, relation::regclass, locktype, mode, granted
from gp_dist_random('pg_locks');
查看具体什么语句持有的锁
select gp_execution_dbid() dbid,procpid,current_query
from gp_dist_random('pg_stat_activity')
where procpid in
(select pid from gp_dist_random('pg_locks') where locktype='relation' and mode='ExclusiveLock');
通过以上语句大概定位到持有锁的segment
segment节点：
根据实际情况进行处理
1.连接相关segment,xxxx替换为实际segment节点的ip,端口，库名
PGOPTIONS="-c gp_session_role=utility" psql -h xxxxxxxxx -p xxxx -d xxxxx
2.在segment查询相关锁情况
SELECT
w.current_query as waiting_query,
w.procpid as w_pid,
w.usename as w_user,
l.current_query as locking_query,
l.procpid as l_pid,
l.usename as l_user,
t.schemaname || '.' || t.relname as tablename
from pg_stat_activity w
join pg_locks l1 on w.procpid = l1.pid and not l1.granted
join pg_locks l2 on l1.relation = l2.relation and l2.granted
join pg_stat_activity l on l2.pid = l.procpid
join pg_stat_user_tables t on l1.relation = t.relid
where w.waiting;
3.处理持有锁的pid
select pg_terminate_backend('procpid');
select pg_terminate_backend(310252);
select pg_cancel_backend(308045);
select procpid from pg_stat_activity where DATNAME = 'BI_DW';
Linux命令：kill -9 procpid