object type SCHEMA_EXPORT/VIEW/VIEW
Processing object type SCHEMA_EXPORT/TABLE/CONSTRAINT/REF_CONSTRAINT
Processing object type SCHEMA_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
. . exported "SCOTT"."SM_TEST" 6.406 MB 66611 rows
. . exported "SCOTT"."DEPT" 5.859 KB 1 rows
. . exported "SCOTT"."EMP" 8.359 KB 9 rows
. . exported "SCOTT"."SALGRADE" 5.835 KB 3 rows
. . exported "SCOTT"."BONUS" 0 KB 0 rows
Master table "SYS"."SYS_EXPORT_SCHEMA_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SYS.SYS_EXPORT_SCHEMA_01 is:
/u01/app/admin/sicsdb/dpdump/TEST_2.dmp
Job "SYS"."SYS_EXPORT_SCHEMA_01" successfully completed at Mon Nov 23 13:51:48 2015 elapsed 0 00:00:16
采样比例在Schema下所有数据表范围内生效，所有数据表基本上以50%的比例进行采样处理。
最后，如果我们导出多张数据表，只对某些数据表进行采样处理，那么如何指定sample参数呢？
[oracle@localhost ~]$ expdp \"/ as sysdba\" dumpfile=TEST_3.dmp schemas=scott sample=scott.sm_test:30
Export: Release 11.2.0.4.0 - Production on Mon Nov 23 13:52:50 2015
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 "SYS"."SYS_EXPORT_SCHEMA_01": "/******** AS SYSDBA" dumpfile=TEST_3.dmp schemas=scott sample=scott.sm_test:30
Estimate in progress using BLOCKS method...
Processing object type SCHEMA_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 4.987 MB
Processing object type SCHEMA_EXPORT/USER
Processing object type SCHEMA_EXPORT/SYSTEM_GRANT
Processing object type SCHEMA_EXPORT/ROLE_GRANT
Processing object type SCHEMA_EXPORT/DEFAULT_ROLE
Processing object type SCHEMA_EXPORT/PRE_SCHEMA/PROCACT_SCHEMA
Processing object type SCHEMA_EXPORT/TABLE/TABLE
Processing object type SCHEMA_EXPORT/TABLE/GRANT/OWNER_GRANT/OBJECT_GRANT
Processing object type SCHEMA_EXPORT/TABLE/INDEX/INDEX
Processing object type SCHEMA_EXPORT/TABLE/CONSTRAINT/CONSTRAINT
Processing object type SCHEMA_EXPORT/TABLE/INDEX/STATISTICS/INDEX_STATISTICS
Processing object type SCHEMA_EXPORT/VIEW/VIEW
Processing object type SCHEMA_EXPORT/TABLE/CONSTRAINT/REF_CONSTRAINT
Processing object type SCHEMA_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
. . exported "SCOTT"."SM_TEST" 3.861 MB 40146 rows
. . exported "SCOTT"."DEPT" 5.960 KB 5 rows
. . exported "SCOTT"."EMP" 8.562 KB 14 rows
. . exported "SCOTT"."SALGRADE" 5.859 KB 5 rows
. . exported "SCOTT"."BONUS" 0 KB 0 rows
Master table "SYS"."SYS_EXPORT_SCHEMA_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SYS.SYS_EXPORT_SCHEMA_01 is:
/u01/app/admin/sicsdb/dpdump/TEST_3.dmp
Job "SYS"."SYS_EXPORT_SCHEMA_01" successfully completed at Mon Nov 23 13:53:00 2015 elapsed 0 00:00:09
从上面实验中，如果只是针对特定数据表进行采样处理，需要通过数据表名:采样比例方式来指定。
3、结论
根据笔者的猜测，sample参数在expdp中主要是传导到select语句的sample语句来实现。