11G新特性，explain plan 可以评估出索引大小

ops$admin@CRMG>explain plan for
2 create index ttt on aaaa(id);

Explained.

ops$admin@CRMG>@display

PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 2861610204

-------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------
| 0 | CREATE INDEX STATEMENT | | 409 | 5317 | 4 (0)| 00:00:01 |
| 1 | INDEX BUILD NON UNIQUE| TTT | | | | |
| 2 | SORT CREATE INDEX | | 409 | 5317 | | |
| 3 | TABLE ACCESS FULL | AAAA | 409 | 5317 | 3 (0)| 00:00:01 |
-------------------------------------------------------------------------------

Note
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- estimated index size: 65536 bytes

14 rows selected.