ESTIMATE
默认：blocks
指定计算每张表使用磁盘空间的方法
ESTIMATE=[BLOCKS | STATISTICS]
1.BLOCKS - 通过块数和块大小计算?
2.STATISTICS -每张表的统计信息计算

限制
1.如果压缩了表，那么使用ESTIMATE=BLOCKS计算的值时不准确的，这个时候就应该使用ESTIMATE=STATISTICS.?
2.在QUERY，REMAP_DATA参数使用的情况下也不准确
?[oracle@lzl ~]$ expdp scott/tiger TABLES=emp ESTIMATE=STATISTICS DIRECTORY=lzl_dir DUMPFILE=estimate_stat.dmp
Export: Release 11.2.0.3.0 - Production on Wed Jul 12 23:29:44 2017
Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.
Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
Starting "SCOTT"."SYS_EXPORT_TABLE_01":  scott/******** TABLES=emp ESTIMATE=STATISTICS DIRECTORY=lzl_dir 
Estimate in progress using STATISTICS method...
Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
.  estimated "SCOTT"."EMP"                               8.203 KB   -预估大小
Total estimation using STATISTICS method: 8.203 KB
Processing object type TABLE_EXPORT/TABLE/TABLE
Processing object type TABLE_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
. . exported "SCOTT"."EMP"                               8.562 KB      14 rows   -实际大小
Master table "SCOTT"."SYS_EXPORT_TABLE_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SCOTT.SYS_EXPORT_TABLE_01 is:
  /home/oracle/expdat.dmp
Job "SCOTT"."SYS_EXPORT_TABLE_01" successfully completed at 23:29:49


ESTIMATE_ONLY
默认：no
如果 ESTIMATE_ONLY=YES, 只预估导出占用的空间不会做实际的导出工作。可用用来预估导出空间
限制：
不能与 QUERY参数一起使用