Let’s say we have a very big table, and for testing purpose, we need only a subset of data i.e to let’s say 10 percent of data from that table, then SAMPLE parameter can be used in EXPDP. We will explain its use in below demo.

SAMPLE
Percentage of data to be exported.

DEMO:

SQL> select count(*) from DBACLASS.OBJECT_LIST;

  COUNT(*)
----------
    219456

PARFILE WITH SAMPLE OF 10 PERCENT.

 cat exp_sample.par

dumpfile=dbaclass_estim.dmp
logfile=dbaclass.log
directory=EXPDIR
tables=DBACLASS.OBJECT_LIST
sample=10

expdp parfile=exp_sample.par
Export: Release 12.1.0.2.0 - Production on Mon Nov 19 12:52:01 2018

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Username: / as sysdba

Connected to: Oracle Database 12c Enterprise Edition Release 12.1.0.2.0 - 64bit Production
With the Partitioning, OLAP, Advanced Analytics and Real Application Testing options
Starting "SYS"."SYS_EXPORT_TABLE_01": /******** AS SYSDBA parfile=exp_sample.par
Estimate in progress using BLOCKS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
Total estimation using BLOCKS method: 2.899 MB
Processing object type TABLE_EXPORT/TABLE/TABLE
Processing object type TABLE_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
Processing object type TABLE_EXPORT/TABLE/STATISTICS/MARKER
. . exported "DBACLASS"."OBJECT_LIST" 2.472 MB 21890 rows --- >>>
Master table "SYS"."SYS_EXPORT_TABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SYS.SYS_EXPORT_TABLE_01 is:
/export/home/oracle/dbaclass_estim.dmp
Job "SYS"."SYS_EXPORT_TABLE_01" successfully completed at Mon Nov 19 12:52:07 2018 elapsed 0 00:00:04

It has exported around 21890 rows which are around 10 percent of actual rows in the table (219456).