数据泵造成的数据损失

客户尝试导入一个分区表的个别几个分区，结果却损失了整个分区表的数据。
下面通过一个例子来在线这个问题：
SQL> CREATE TABLE T_PART PARTITION BY RANGE (CREATED)
2 (PARTITION P1 VALUES LESS THAN (TO_DATE(‘2012-1-1’, ‘YYYY-MM-DD’)),
3 PARTITION P2 VALUES LESS THAN (TO_DATE(‘2012-2-1’, ‘YYYY-MM-DD’)),
4 PARTITION P3 VALUES LESS THAN (TO_DATE(‘2012-3-1’, ‘YYYY-MM-DD’)),
5 PARTITION P4 VALUES LESS THAN (TO_DATE(‘2012-4-1’, ‘YYYY-MM-DD’)),
6 PARTITION PMAX VALUES LESS THAN (MAXVALUE))
7 AS SELECT * FROM DBA_OBJECTS;
Table created.
SQL> host expdp test directory=d_output dumpfile=t_part.dp logfile=t_part.log tables=t_part:p3, t_part:p4
Export: Release 11.2.0.3.0 – Production on Tue Mar 13 12:17:00 2012
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.
Password:
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 – 64bit Production
With the Partitioning, Oracle Label Security and Real Application Testing options
Starting “TEST”.”SYS_EXPORT_TABLE_01″: test/******** directory=d_output dumpfile=t_part.dp logfile=t_part.log tables=t_part:p3, t_part:p4
Estimate in progress using BLOCKS method…
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 16 MB
Processing object type TABLE_EXPORT/TABLE/TABLE
. . exported “TEST”.”T_PART”:”P3″ 29.89 KB 193 rows
. . exported “TEST”.”T_PART”:”P4″ 65 KB 425 rows
Master table “TEST”.”SYS_EXPORT_TABLE_01″ successfully loaded/unloaded
******************************************************************************
Dump file set for TEST.SYS_EXPORT_TABLE_01 is:
/home/oracle/t_part.dp
Job “TEST”.”SYS_EXPORT_TABLE_01″ successfully completed at 12:17:17
客户尝试导入几个分区，但是这些分区并不为空，于是在导入时指定了错误的TABLE_EXISTS_ACTION参数为REPLACE：
SQL> host impdp test directory=d_output dumpfile=t_part.dp logfile=t_part_imp.log tables=t_part:p3 table_exists_action=replace
Import: Release 11.2.0.3.0 – Production on Tue Mar 13 14:51:55 2012
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.
Password:
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 – 64bit Production
With the Partitioning, Oracle Label Security and Real Application Testing options
Master table “TEST”.”SYS_IMPORT_TABLE_01″ successfully loaded/unloaded
Starting “TEST”.”SYS_IMPORT_TABLE_01″: test/******** directory=d_output dumpfile=t_part.dp logfile=t_part_imp.log tables=t_part:p3 table_exists_action=replace
Processing object type TABLE_EXPORT/TABLE/TABLE
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
. . imported “TEST”.”T_PART”:”P3″ 29.89 KB 193 rows
Job “TEST”.”SYS_IMPORT_TABLE_01″ successfully completed at 14:52:00
虽然导入的时候仅指定了一个分区，但是Oracle并不会对这一个分区执行TRUNCATE操作，而是将整个表DROP掉，然后利用数据泵中的源数据重建。
SQL> SELECT COUNT(*) FROM T_PART PARTITION (P1);
COUNT(*)
———-
0
SQL> SELECT COUNT(*) FROM T_PART PARTITION (P2);
COUNT(*)
———-
0
SQL> SELECT COUNT(*) FROM T_PART PARTITION (P3);
COUNT(*)
———-
193
SQL> SELECT COUNT(*) FROM T_PART PARTITION (P4);
COUNT(*)
———-
0
SQL> SELECT COUNT(*) FROM T_PART PARTITION (PMAX);
COUNT(*)
———-
0
这个表中只有导入的分区记录存在，原则上impdp对应的数据泵导出文件中的记录也都是可以恢复的，但是表中其他的分区数据则完全丢失。
而且Oracle在删除的时候还使用PURGE选项，使得分区表在删除的时候并没有被放到回收站中，而是直接从数据库中被清除。从这一点上讲，Oracle应该去掉PURGE语句，或者至少给出一个选项，毕竟DROP TABLE对于系统来说有风险的。
最近碰到两三次的问题都是和imp以及impdp有关，因此只要是涉及到数据库修改的，还是要谨慎处之。