因为数据库空间不足，需要对历史数据进行清理，查询涉及的表竟然有550G，和开发沟通之后将历史数据使用应用程序迁移到其他机器上，之后对旧表进行删除！(对于此种情况多少有些无奈，入职之前表已经存在了，建表的时候应该考虑使用分区表，清理数据会更方便)
查看表的大小
YANG@yangdb>set timing on;
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 550.075195
Elapsed: 00:00:00.98
YANG@yangdb>
使用 truncate的reuse storage 特性，默认时是drop storage，这样会直接对object占用的删除之后并不直接drop storage ，这样可以避免回收大量的extent 太多导致系统资源紧张的情况
YANG@yangdb>truncate table YANG.YANGTAB reuse storage;
Table truncated.
Elapsed: 00:04:19.31
YANG@yangdb>
YANG@yangdb>
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 550.075195
Elapsed: 00:00:00.09
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 563277M;
ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 563277M
*
ERROR at line 1:
ORA-03230: segment only contains 72099438 blocks of unused space above high water mark
Elapsed: 00:00:00.27
第一次 size 设置的有点大！
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 503277M;
Table altered.
Elapsed: 00:00:17.99
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 491.481628
Elapsed: 00:00:00.03
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 453277M;
Table altered.
Elapsed: 00:00:14.50
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 442.653503
Elapsed: 00:00:00.03
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 403277M;
Table altered.
Elapsed: 00:00:14.86
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 393.825378
Elapsed: 00:00:00.03
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 323277M;
Table altered.
Elapsed: 00:00:22.53
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 315.700378
Elapsed: 00:00:00.02
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 253277M;
Table altered.
Elapsed: 00:00:28.05
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 247.341003
Elapsed: 00:00:00.02
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 183277M;
Table altered.
Elapsed: 00:00:54.36
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 178.981628
Elapsed: 00:00:00.13
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 123277M;
Table altered.
Elapsed: 00:00:33.64
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 120.387878
Elapsed: 00:00:00.03
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 83277M;
Table altered.
Elapsed: 00:00:22.36
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 81.3253784
Elapsed: 00:00:00.03
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 53277M;
Table altered.
Elapsed: 00:00:14.35
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 52.0285034
Elapsed: 00:00:00.02
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 33277M;
Table altered.
Elapsed: 00:00:09.40
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 32.4972534
Elapsed: 00:00:00.02
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 13277M;
Table altered.
Elapsed: 00:00:09.29
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 12.9660034
Elapsed: 00:00:00.02
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 3277M;
Table altered.
Elapsed: 00:00:04.44
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 3.20037842
Elapsed: 00:00:00.02
YANG@yangdb>ALTER table YANG.YANGTAB DEALLOCATE UNUSED KEEP 277M;
Table altered.
Elapsed: 00:00:03.08
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB .270690918
Elapsed: 00:00:00.07
YANG@yangdb>drop table YANG.YANGTAB;
Table dropped.
Elapsed: 00:00:01.11
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB_NEW';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB_NEW 83.7783203
Elapsed: 00:00:00.09
Elapsed: 00:00:00.01
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB_NEW';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB_NEW 83.7783203
YANG@yangdb>rename YANGTAB_new to YANGTAB;
Table renamed.
Elapsed: 00:00:00.10
YANG@yangdb>SELECT segment_name,bytes/1024/1024/1024 FROM user_Segments WHERE segment_name='YANGTAB';
SEGMENT_NAME BYTES/1024/1024/1024
------------------------------ --------------------
YANGTAB 83.7783203
Elapsed: 00:00:00.03
YANG@yangdb>
Elapsed: 00:00:00.03
附上操作过程中遇到的低级错误
1 oracle 和mysql 之间对表的重命名的语法混淆了，汗！
YANG@yangdb>rename table YANG.YANGTAB_new to YANG.YANGTAB;
rename table YANG.YANGTAB_new to YANG.YANGTAB
*
ERROR at line 1:
ORA-00903: invalid table name
2 表名不允许带owner
YANG@yangdb>rename YANG.YANGTAB_new to YANG.YANGTAB;
rename YANG.YANGTAB_new to YANG.YANGTAB
*
ERROR at line 1:
ORA-01765: specifying owner s name of the table is not allowed
Elapsed: 00:00:00.01
参考自己的另一篇文章
