rebuild时也会使用临时表空间

ask tom上关于rebuild index 有这么一段话：

If you need to rebuild your indexes, you need 2x the space -- you'll have the old and the new index for a period of time. If you do it online, you'll need additional space to hold the changes that are made during the rebuild as well2×的空间是当前index所在的tablespace中使用空间

排序操作相关的 stat号

SQL> select name,statistic# from v$statname where name like '%sort%';

NAME                                                             STATISTIC# ---------------------------------------------------------------- ---------- sorts (memory)                                                          341 sorts (disk)                                                            342 sorts (rows)                                                            343

SQL> select STATISTIC#,value from v$mystat where STATISTIC# in (341,342,343);

STATISTIC#      VALUE

---------- ----------        341       1384        342         12        343   19144681

SQL> alter index idx_name rebuild online;

Index altered.

SQL> select STATISTIC#,value from v$mystat where STATISTIC# in (341,342,343);

STATISTIC#      VALUE

---------- ----------        341       1405        342         13        343   20739817

可以看出各种sort stat都增加了。

SQL> alter index idx_name rebuild;

Index altered.

SQL> select STATISTIC#,value from v$mystat where STATISTIC# in (341,342,343);

STATISTIC#      VALUE

---------- ----------        341       1405        342         14        343   22334953

在rebulid index online的时候走的是full table scan，这时候也是需要排序的，而且排序的次数会比较多