Oracle等待事件之01(Buffer busy waits)

1. 創建測試用表

[oracle@DB01 bin]$ sql xag/[email protected]:1521/MPTEST;

SQL> set sqlformat ansiconsole;

create table test_wait(id int,name varchar2(10));

begin
  for i in 1..20 loop
   insert into test_wait values (i,'usr'||i);
  end loop;
  commit;
end;
/

SQL> select id,rowid,
      dbms_rowid.rowid_object(rowid)  as "object_id(数据对象号)",
      dbms_rowid.rowid_relative_fno(rowid) as "file_id(相对文件号)",
      dbms_rowid.rowid_block_number(rowid) as "block_id(在第几个块)",
      dbms_rowid.rowid_row_number(rowid) as "num(在block中的行数)"
    from test_wait;
ID  ROWID               object_id(数据对象号)  file_id(相对文件号)  block_id(在第几个块)  num(在block中的行数)  
1   AAAUKcAFyAAAACjAAA  82588                 370                 163                  0                
2   AAAUKcAFyAAAACjAAB  82588                 370                 163                  1                
3   AAAUKcAFyAAAACjAAC  82588                 370                 163                  2                
4   AAAUKcAFyAAAACjAAD  82588                 370                 163                  3                
5   AAAUKcAFyAAAACjAAE  82588                 370                 163                  4                
6   AAAUKcAFyAAAACjAAF  82588                 370                 163                  5                
7   AAAUKcAFyAAAACjAAG  82588                 370                 163                  6                
8   AAAUKcAFyAAAACjAAH  82588                 370                 163                  7                
9   AAAUKcAFyAAAACjAAI  82588                 370                 163                  8                
10  AAAUKcAFyAAAACjAAJ  82588                 370                 163                  9                
11  AAAUKcAFyAAAACjAAK  82588                 370                 163                  10               
12  AAAUKcAFyAAAACjAAL  82588                 370                 163                  11               
13  AAAUKcAFyAAAACjAAM  82588                 370                 163                  12               
14  AAAUKcAFyAAAACjAAN  82588                 370                 163                  13               
15  AAAUKcAFyAAAACjAAO  82588                 370                 163                  14               
16  AAAUKcAFyAAAACjAAP  82588                 370                 163                  15               
17  AAAUKcAFyAAAACjAAQ  82588                 370                 163                  16               
18  AAAUKcAFyAAAACjAAR  82588                 370                 163                  17               
19  AAAUKcAFyAAAACjAAS  82588                 370                 163                  18               
20  AAAUKcAFyAAAACjAAT  82588                 370                 163                  19 

2. 測試等待事件

#會話1
#查看当前用户的sid和serial#:
SQL> select sid, serial#, status from v$session where audsid=userenv('sessionid');
SID  SERIAL#  STATUS  
782  15440    ACTIVE 

begin 
 for i in 1..5000000 loop
   update test_wait set name='session 1' where id=1;
   commit;
 end loop;
end;
/

#新開會話2
[oracle@DB01 XAG]$ sql xag/[email protected]:1521/MPTEST;
SQL> set sqlformat ansiconsole;

#查看当前用户的sid和serial#:
SQL> select sid, serial#, status from v$session where audsid=userenv('sessionid');
SID   SERIAL#  STATUS  
1199  5993     ACTIVE

begin 
 for i in 1..5000000 loop
   update test_wait set name='session 2' where id=2;
   commit;
 end loop;
end;
/

#新開會話3
[oracle@DB01 XAG]$ sql xag/[email protected]:1521/MPTEST;

SQL> set sqlformat ansiconsole;

#查看当前用户的sid和serial#:
SQL> select sid, serial#, status from v$session where audsid=userenv('sessionid');
SID  SERIAL#  STATUS  
113  22734    ACTIVE  

#查看全部會話
SQL> select username,sid,serial# from v$session where username is not null;
USERNAME  SID   SERIAL#  
SYS       3     10073    
XAG       113   22734    
XAG       782   15440    
XAG       1199  5993 

#查詢等待事件
SQL> select event,sid,p1,p2,p3 from v$session_wait where sid in (782,1199) and "WAIT_CLASS#"!=6;
EVENT              SID   P1   P2   P3  
buffer busy waits  1199  370  163  1 

SQL> SELECT name,parameter1,parameter2,parameter3 FROM v$event_name WHERE name='buffer busy waits';
NAME               PARAMETER1  PARAMETER2  PARAMETER3  
buffer busy waits  file#       block#      class# 

产生buffer busy waits的对象在file#为370，block_id为163上

#data block产生大量的等待 （8311厘秒=83秒）
SQL> select * from v$waitstat where count>0;
CLASS              COUNT   TIME  CON_ID  
data block         351448  8311  7       
segment header     29      0     7       
1st level bmb      5       0     7       
3rd level bmb      37      1     7       
file header block  10      158   7       
undo header        57533   92    7       
undo block         415     35    7 

#在test_wait 表上产生了热块 
SQL> select sql_text from V$sqlarea  where (address,hash_value) in (select sql_address,sql_hash_value from v$session  where event like '%buffer busy%');
SQL_TEXT                                                                                                                                                                 
begin   for i in 1..5000000 loop    update test_wait set name='session 1' where id=1;    commit;  end loop; end;   
begin   for i in 1..5000000 loop    update test_wait set name='session 2' where id=2;    commit;  end loop; end; 

SQL> select sql_text from v$sqlarea where sql_text like '%test_wait%';
SQL_TEXT                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
begin   for i in 1..5000000 loop    update test_wait set name='session 1' where id=1;    commit;  end loop; end;                                                                                                                         
begin   for i in 1..5000000 loop    update test_wait set name='session 2' where id=2;    commit;  end loop; end;          
                                                                                                                                                   
#查看XAG用户对象TEST_WAIT所在的块：（160-167） 包含上面的 163塊
SQL> select owner,SEGMENT_NAME,SEGMENT_TYPE,FILE_ID,BLOCK_ID,BLOCKS from dba_extents where segment_name='TEST_WAIT';
OWNER  SEGMENT_NAME  SEGMENT_TYPE  FILE_ID  BLOCK_ID  BLOCKS  
XAG    TEST_WAIT     TABLE         370      160       8