基于flashback_scn的expdp导出方法是什么
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在使用10g后的Oracle data pump导出数据时，我们可以使用flashback_scn参数指定导出的时间点，这时
oracle会使用flashback query查询导出scn时的数据，flashback query使用undo，无需打开flashback database功能。
也就是说，只要undo信息不被覆盖，即使数据库被重启，仍然可以进行基于flashback_scn的导出动作。
--以scott用户做测试
oracle@wang:/home/oracle$sqlplus scott/tiger;
SQL*Plus: Release 11.2.0.4.0 Production on Fri Mar 15 07:43:24 2019
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
SQL> show user;
USER is "SCOTT"
SQL> select current_scn from v$database;
CURRENT_SCN
-----------
21870773 (记为1号时间点)
SQL> create table t (num number);
Table created.
SQL> insert into t values(1);
1 row created.
SQL> commit;
Commit complete.
SQL> select current_scn from v$database;
CURRENT_SCN
-----------
21870796 (记为2号时间点)
SQL> insert into t values(2);
1 row created.
SQL> commit;
Commit complete.
SQL> select current_scn from v$database;
CURRENT_SCN
-----------
21870805
SQL> conn / as sysdba
Connected.
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 835104768 bytes
Fixed Size 2257840 bytes
Variable Size 549456976 bytes
Database Buffers 281018368 bytes
Redo Buffers 2371584 bytes
Database mounted.
Database opened.
SQL> select current_scn from v$database;
CURRENT_SCN
-----------
21871307 (记为3号时间点)
SQL> conn scott/tiger;
Connected.
SQL> insert into t values(3);
1 row created.
SQL> commit;
Commit complete.
SQL> select current_scn from v$database;
CURRENT_SCN
-----------
21871340 (记为4号时间点)
SQL> select * from t;
NUM
----------
1
2
3
--现在开始做expdp导出
(1号时间点)
expdp scott/tiger directory=DATA_PUMP_DIR dumpfile=t1.dmp tables=t flashback_scn=21870773
(2号时间点)
expdp scott/tiger directory=DATA_PUMP_DIR dumpfile=t2.dmp tables=t flashback_scn=21870796
(3号时间点)
expdp scott/tiger directory=DATA_PUMP_DIR dumpfile=t3.dmp tables=t flashback_scn=21871307
(4号时间点)
expdp scott/tiger directory=DATA_PUMP_DIR dumpfile=t4.dmp tables=t flashback_scn=21871340
oracle@wang:/home/oracle$ expdp scott/tiger directory=DATA_PUMP_DIR dumpfile=t1.dmp tables=t
flashback_scn=21870773
Export: Release 11.2.0.4.0 - Production on Fri Mar 15 07:52:18 2019
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Starting "SCOTT"."SYS_EXPORT_TABLE_01": scott/******** directory=DATA_PUMP_DIR dumpfile=t1.dmp tables=t flashback_scn=21870773
Estimate in progress using BLOCKS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 64 KB
Processing object type TABLE_EXPORT/TABLE/TABLE
. . exported "SCOTT"."T" 4.984 KB 0 rows
Master table "SCOTT"."SYS_EXPORT_TABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SCOTT.SYS_EXPORT_TABLE_01 is:
/u01/app/oracle/admin/DBdb/dpdump/t1.dmp
Job "SCOTT"."SYS_EXPORT_TABLE_01" successfully completed at Fri Mar 15 07:52:28 2019 elapsed 0 00:00:08
oracle@wang:/home/oracle$ expdp scott/tiger directory=DATA_PUMP_DIR dumpfile=t2.dmp tables=t
flashback_scn=21870796
Export: Release 11.2.0.4.0 - Production on Fri Mar 15 07:52:34 2019
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Starting "SCOTT"."SYS_EXPORT_TABLE_01": scott/******** directory=DATA_PUMP_DIR dumpfile=t2.dmp tables=t flashback_scn=21870796
Estimate in progress using BLOCKS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 64 KB
Processing object type TABLE_EXPORT/TABLE/TABLE
. . exported "SCOTT"."T" 5 KB 1 rows
Master table "SCOTT"."SYS_EXPORT_TABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SCOTT.SYS_EXPORT_TABLE_01 is:
/u01/app/oracle/admin/DBdb/dpdump/t2.dmp
Job "SCOTT"."SYS_EXPORT_TABLE_01" successfully completed at Fri Mar 15 07:52:44 2019 elapsed 0 00:00:07
oracle@wang:/home/oracle$ expdp scott/tiger directory=DATA_PUMP_DIR dumpfile=t3.dmp tables=t
flashback_scn=21871307
Export: Release 11.2.0.4.0 - Production on Fri Mar 15 07:52:54 2019
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Starting "SCOTT"."SYS_EXPORT_TABLE_01": scott/******** directory=DATA_PUMP_DIR dumpfile=t3.dmp tables=t flashback_scn=21871307
Estimate in progress using BLOCKS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 64 KB
Processing object type TABLE_EXPORT/TABLE/TABLE
. . exported "SCOTT"."T" 5.007 KB 2 rows
Master table "SCOTT"."SYS_EXPORT_TABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SCOTT.SYS_EXPORT_TABLE_01 is:
/u01/app/oracle/admin/DBdb/dpdump/t3.dmp
Job "SCOTT"."SYS_EXPORT_TABLE_01" successfully completed at Fri Mar 15 07:53:03 2019 elapsed 0 00:00:07
oracle@wang:/home/oracle$ expdp scott/tiger directory=DATA_PUMP_DIR dumpfile=t4.dmp tables=t
flashback_scn=21871340
Export: Release 11.2.0.4.0 - Production on Fri Mar 15 07:53:12 2019
Copyright (c) 1982, 2011, Oracle and/or its affiliates. All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Starting "SCOTT"."SYS_EXPORT_TABLE_01": scott/******** directory=DATA_PUMP_DIR dumpfile=t4.dmp tables=t flashback_scn=21871340
Estimate in progress using BLOCKS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 64 KB
Processing object type TABLE_EXPORT/TABLE/TABLE
. . exported "SCOTT"."T" 5.015 KB 3 rows
Master table "SCOTT"."SYS_EXPORT_TABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SCOTT.SYS_EXPORT_TABLE_01 is:
/u01/app/oracle/admin/DBdb/dpdump/t4.dmp
Job "SCOTT"."SYS_EXPORT_TABLE_01" successfully completed at Fri Mar 15 07:53:22 2019 elapsed 0 00:00:07
oracle@wang:/home/oracle$
--现在开始做impdp导出
(1号时间点)
drop table t purge;
impdp scott/tiger directory=DATA_PUMP_DIR dumpfile=t1.dmp
(2号时间点)
drop table t purge;
impdp scott/tiger directory=DATA_PUMP_DIR dumpfile=t2.dmp
(3号时间点)
drop table t purge;
impdp scott/tiger directory=DATA_PUMP_DIR dumpfile=t3.dmp
(4号时间点)
drop table t purge;
impdp scott/tiger directory=DATA_PUMP_DIR dumpfile=t4.dmp
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