一个表无法truncate但是可以rename，这个乍听起来觉得好奇怪，下面模拟该过程。 3个session： session1执行truncate和rename操作； session2执行lock表操作； session3进行监控。 session1： [gpadmin@wx60 contrib]$ psql gtlionspsql (8.2.15)Type help for
一个表无法truncate但是可以rename，这个乍听起来觉得好奇怪，下面模拟该过程。[gpadmin@wx60 contrib]$ psql gtlions psql (8.2.15) Type "help" for help. gtlions=# \d test Table "public.test" Column | Type | Modifiers --------+------------------------+----------- id | integer | name | character varying(200) | Indexes: "idxtestid" btree (id) "idxtestname" btree (name) Distributed by: (id) gtlions=# select pg_backend_pid(); pg_backend_pid ---------------- 1473 (1 row) gtlions=# truncate table test; Cancel request sent ERROR: relation "test" does not exist gtlions=# alter table test rename to test1; ALTER TABLE
[gpadmin@wx60 ~]$ psql gtlions psql (8.2.15) Type "help" for help. gtlions=# select pg_backend_pid(); pg_backend_pid ---------------- 1555 (1 row) gtlions=# begin; BEGIN gtlions=# select * from test limit 10; id | name -------+------------ 19672 | 19672-asfd 19674 | 19674-asfd 19676 | 19676-asfd 19678 | 19678-asfd 19680 | 19680-asfd 19682 | 19682-asfd 19684 | 19684-asfd 19686 | 19686-asfd 19688 | 19688-asfd 19690 | 19690-asfd (10 rows) gtlions=# end; COMMIT
[gpadmin@wx60 ~]$ psql gtlions psql (8.2.15) Type "help" for help. gtlions=# select locktype,relation::regclass,pid,mode,granted,gp_segment_id from pg_locks where pid in (1473,1555) order by pid; locktype | relation | pid | mode | granted | gp_segment_id ----------+----------+-----+------+---------+--------------- (0 rows) gtlions=# select locktype,relation::regclass,pid,mode,granted,gp_segment_id from pg_locks where pid in (1473,1555) order by pid; locktype | relation | pid | mode | granted | gp_segment_id ---------------+-------------+------+-----------------+---------+--------------- relation | test | 1555 | AccessShareLock | t | -1 relation | idxtestname | 1555 | AccessShareLock | t | -1 transactionid | | 1555 | ExclusiveLock | t | -1 relation | idxtestid | 1555 | AccessShareLock | t | -1 (4 rows) gtlions=# select locktype,relation::regclass,pid,mode,granted,gp_segment_id from pg_locks where pid in (1473,1555) order by pid; locktype | relation | pid | mode | granted | gp_segment_id ---------------+-------------+------+---------------------+---------+--------------- transactionid | | 1473 | ExclusiveLock | t | -1 relation | test | 1473 | AccessExclusiveLock | f | -1 transactionid | | 1555 | ExclusiveLock | t | -1 relation | idxtestid | 1555 | AccessShareLock | t | -1 relation | idxtestname | 1555 | AccessShareLock | t | -1 relation | test | 1555 | AccessShareLock | t | -1 (6 rows)