v$waitstat和xbh.class的关系如何？
x$bh.class 中的分类，依次对应于 v$waitstat 中记录 SQL> select * from v$version; BANNER ---------------------------------------------------------------- Oracle9i Enterprise Edition Release 9.2.0.1.0 - Production PL/SQL Release 9.2.0.1.0 - Production CORE 9.2.0.1.0 Production TNS for 32-bit Windows: Version 9.2.0.1.0 - Production NLSRTL Version 9.2.0.1.0 - Production SQL> SQL> select * from v$waitstat; CLASS COUNT TIME ------------------ ---------- ---------- data block 2 1 sort block 0 0 save undo block 0 0 segment header 1 0 save undo header 0 0 free list 0 0 extent map 0 0 1st level bmb 0 0 2nd level bmb 0 0 3rd level bmb 0 0 bitmap block 0 0 CLASS COUNT TIME ------------------ ---------- ---------- bitmap index block 0 0 file header block 0 0 unused 0 0 system undo header 0 0 system undo block 0 0 undo header 0 0 undo block 0 0 已选择18行。 SQL> SQL> select distinct class from x$bh order by class ; CLASS ---------- 1 4 8 9 12 13 15 17 从这里开始依次为undo header /undo block 18 19 20 CLASS ---------- 21 22 23 24 25 26 27 28 29 30 31 CLASS ---------- 32 33 34 35 36 已选择27行。 SQL> oracle 7 非系统回滚段是从9开始，8i是从13开始 从这里，基本就可以明白，v$waitstat 就是针对 data buffer 中各类型的block的等待进行统计的