Can rename table but can not truncate table，renametruncate

Can rename table but can not truncate table，renametruncate

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 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

 
session2：

[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

 
session3：

[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)

 
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because your table is a partition table ,so you can not truncate it immediately。
perhaps you can truncate it by partition.or,you can delete it direct.
and then,create table temp as select * from yourtable where rownum<1,then drop your table.
perhaps can help you!
give your withs！
 

删除所有行不代表删除所有的东西，就像你的windows一样，你删除了一个盘下所有的数据，你的盘就会消失吗？
不可能吧，你只不过是把非系统盘的数据删除了，你的盘卷标、统计信息，盘符的大小之类的都在啊
只有你删除这个盘符的物理信息，重新格式化的时候盘才会消失，这在数据库中就是drop，使用drop table，才会将这张表从根本上删掉，一切约束结构也才会消失