模拟产生CBC LATCH与buffer busy wait等待事件

  数据库版本：11.2.0.4.0

1.查出表TEST相关信息

select rowid,
dbms_rowid.rowid_row_number(rowid) rowid_rownum,
dbms_rowid.rowid_relative_fno(rowid) file_id,
dbms_rowid.rowid_block_number(rowid) block_id,test.* from test;
ROWID              ROWID_ROWNUM    FILE_ID   BLOCK_ID OBJECT_NAME  STATUS
------------------ ------------ ---------- ---------- ------------ -------
AAAFSJAAEAAAACkAAA            0           4        164 10           15
AAAFSJAAEAAAACkAAB            1           4        164 10           15
可以看到，TEST表的两条记录在同一文件的同一个BLOCK中。

2.写一个循环：

循环执行查询语句一百万次： --查询164数据块的第一行
declare
aa varchar2(100);
begin
for i in 1..1000000 loop
select object_name into aa from test where rowid='AAAFSJAAEAAAACkAAA';
end loop;
end;
/

循环更新查询语句200次     --查询164数据块的第二行
declare
begin
for i in 1..200 loop
update test set status=15 where rowid='AAAFSJAAEAAAACkAAB';
end loop;
commit;
end;
/

3.打开两个会话，查出会话SID。--这里会话SID分别是30 35.

在30号会话执行循环查询：
BYS@ bys3>select sid from v$mystat where rownum=1;
       SID
----------
        30
节约篇幅，执行循环的语句就不贴了。

在35号会话执行循环更新语句：
BYS@ bys3>select sid from v$mystat where rownum=1;
       SID
----------
        35
节约篇幅，执行循环的语句就不贴了。

4.再打开一个会话，使用语句查询35 30号会话的等待事件

23:03:20 SYS@ bys3>select sid ,event,total_waits,total_timeouts,time_waited_micro from v$session_event  
23:03:21   2  where sid in(30,35);

       SID EVENT                                    TOTAL_WAITS TOTAL_TIMEOUTS TIME_WAITED_MICRO
---------- ---------------------------------------- ----------- -------------- -----------------
        30 buffer busy waits                                  1              0               968             --------这里30号会话是读操作，35号会话是写操作，也就是30号会话的读被写阻塞。
        30 latch: In memory undo latch                        1              0               960
        30 resmgr:cpu quantum                                 3              0             33589
        30 SQL*Net message to client                         15              0               637
        30 SQL*Net message from client                       14              0         206010788
        35 Disk file operations I/O                           3              0               312
        35 latch: cache buffers chains                        2              0              1174
        35 db file sequential read                           64              0              9065
        35 direct path read                                 100              0             53191
        35 SQL*Net message to client                         25              0               259
        35 SQL*Net message from client                       24              0         625117659
        35 SQL*Net break/reset to client                      4              0              1046

12 rows selected.

Elapsed: 00:00:00.02
23:03:22 SYS@ bys3>select sid ,event,total_waits,total_timeouts,time_waited_micro from v$session_event
23:03:30   2  where sid in(30,35) and event like '%buffer%';

       SID EVENT                                    TOTAL_WAITS TOTAL_TIMEOUTS TIME_WAITED_MICRO
---------- ---------------------------------------- ----------- -------------- -----------------
        30 buffer busy waits                                  1              0               968
        35 latch: cache buffers chains                        2              0              1174

Elapsed: 00:00:00.03
查看等待事件截图：