Wednesday, August 28, 2013

All About Blocking Locks in Oracle

A  very  nice  post  has  been  written  by  Oracle  Ace Director  Arup Nanda  about the  Blocking  Locks . It  is  so simple  and  brilliantly explained . Check  the  below  link  and  enjoy  reading  about  basic  concepts behind locks . Before going to this link , read my previous post on ITL ( Interested Transaction List)  for better understading of this post .

Another  Brilliant  demo  on  Blocking  lock is  explained  by  "Natalka Roshak" .  She  has so wonderfully  explained .  Enjoy reading this link too. 

Here,  i  have  added  few  more query on  locks along  with  it's output . For  demo purpose , i  have created  a  table "blck_tab"  and  locked this  table manually  and accessing this locked table from other sessions .Let's have a look .

SQL> create table blck_tab (id number , name varchar(22));
Table created.

SQL> insert into blck_tab values(1,'abc');
1 row created.

SQL> insert into blck_tab values(2,'xyz');
1 row created.

SQL> insert into blck_tab values(3,'pqr');
1 row created.

SQL> commit;
Commit complete.

SQL> select * from blck_tab  for update ;             ----- Table Locked
        ID               NAME
----------    ----------------------
         1                   abc
         2                   xyz
         3                   pqr

Session 1 : 

SQL>conn test1/test1
SQL> update test.blck_tab set name='qwert' where id=3;
--->>  Waiter   <---- 

Session 2 : 

SQL> conn hr/hr
SQL> delete test.blck_tab where id=1;
--->>  Waiter   <---- 

Query to check locks :
(For Non-RAC)
  3  FROM   V$LOCK
  5  ORDER BY block DESC;
------     ------------       ----------
    37            YES                 NO
    34             NO                 YES
    31             NO                  YES

SQL> select l1.sid, ' IS BLOCKING ', l2.sid
  2  from gv$lock l1, gv$lock l2
  3  where l1.block >0 and l2.request > 0
  4  and l1.id1=l2.id1
  5  and l1.id2=l2.id2;
       SID    'ISBLOCKING'         SID
----------  ------------------      --------
        37      IS BLOCKING          31
        37      IS BLOCKING          34

For RAC 
SQL>select distinct s1.username || '@' || s1.machine || ' ( INST=' || s1.inst_id || ' SID=' || s1.sid || ' )  is blocking '|| s2.username || '@' || s2.machine || ' ( INST=' || s1.inst_id || ' SID=' || s2.sid || ' ) ' AS blocking_status from gv$lock l1, gv$session s1, gv$lock l2, gv$session s2 where s1.sid=l1.sid and s2.sid=l2.sid and l1.BLOCK>0 and l2.request > 0and l1.id1 = l2.id1 and l2.id2 = l2.id2 and l1.inst_id = s1.inst_id;


Expanded Lock  Query
SQL> SELECT vs.username,  vs.osuser,   vh.sid locking_sid,  vs.status status,
 vs.module module,   vs.program program_holding,   jrh.job_name,   vsw.username,
 vsw.osuser,   vw.sid waiter_sid,   vsw.program program_waiting,  jrw.job_name,
 'alter system kill session ' || ''''|| vh.sid || ',' || vs.serial# || ''';'  "Kill_Command"
FROM  v$lock vh,  v$lock vw,  v$session vs,  v$session vsw,
 dba_scheduler_running_jobs jrh,
 dba_scheduler_running_jobs jrw
WHERE     (vh.id1, vh.id2) IN (SELECT id1, id2  
 FROM v$lock
 WHERE request = 0
 SELECT id1, id2
 FROM v$lock
 WHERE lmode = 0)
 AND vh.id1 = vw.id1
 AND vh.id2 = vw.id2
 AND vh.request = 0
 AND vw.lmode = 0
 AND vh.sid = vs.sid
 AND vw.sid = vsw.sid
 AND vh.sid = jrh.session_id(+)
 AND vw.sid = jrw.session_id(+);

Blocking locks with Sid and SQl 

SQL> set lines 200
column pu format a8 heading 'O/S|login|ID' justify left
column su format a15 heading 'Oracle/User ID' justify left
column prog format a15 heading 'Program' justify left
column machine format a15 heading 'machine' justify left
column stat format a8 heading 'Session|Status' justify left
column sser format 999999 heading 'Oracle|Serial|No' justify right
column txt format a28 word heading 'SQL TEXT' 
column RUNT format a15 word heading 'Run Time' 
set pagesize 1000
 s.username su,
 s.program prog,
 s.sid sid,
 lpad(p.spid,7) pid,
 substr(sa.sql_text,1,2000) txt,
 ltrim(to_char(floor(s.last_call_et/3600),'00009')) ||':'
 || ltrim(to_char(floor(mod(s.last_call_et,3600)/60),'09')) ||':'
 || ltrim(to_char(mod(s.last_call_et,60),'09')) RUNT
from v$process p,
 v$session s,
 v$sqlarea sa
where p.addr = s.paddr
 and s.username is not null
 and s.sql_address=sa.address(+)
 and s.sql_hash_value=sa.hash_value(+)
 and s.sid in (SELECT   SID FROM     V$LOCK WHERE    REQUEST > 0 OR BLOCK > 0)
order by 1,2
Oracle/User ID  Program           SID     PID          SQL TEXT                                  Run Time
--------------- ---------------          ------- -------   ----------------------------                ---------------
HR              sqlplus.exe             31        2812    delete test.blck_tab where         00001:32:11

TEST            sqlplus.exe             37    1928                                                          00000:06:35
TEST1           sqlplus.exe             34    1880       update test.blck_tab set            00002:11:34
                                                                            name='qwert' where id=3

Blocker/Waiter object details

SQL> col object_name for a28
SQL> col owner for a15
SQL> select do.owner,do.object_name , row_wait_obj#, row_wait_file#, row_wait_block#, row_wait_row#, dbms_rowid.rowid_create (1, ROW_WAIT_OBJ#, ROW_WAIT_FILE#,ROW_WAIT_BLOCK#, ROW_WAIT_ROW#)
  2  from
  3  v$session s,
  4  dba_objects do
  5  where sid in (select l2.sid blocking from v$lock l1, v$lock l2 where l1.block =1 and l2.request > 0 and l1.id1=l2.id1 and l1.id2=l2.id2) and
  6  s.ROW_WAIT_OBJ# = do.OBJECT_ID;

--------------- -------------- ------------- -------------- --------------- ------------- ------------------
TEST            BLCK_TAB        74697              4             524             2          AAASPJAAEAAAAIMAAC

TEST            BLCK_TAB        74697              4             524             0          AAASPJAAEAAAAIMAAA

Note for RAC  use  gv$ instead of v$ .

Enjoy    :-) 


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