How do you find out who is locking a specific row in a table?

1- Select the sid and other desired columns from v$session where lockwait is not null

2- Select * from v$lock where sid = the sid(s) from the prior step

3- Look at the ID1 column for the requested but not held lock

4- Select * from v$lock where ID1 = the ID1 value returned in the prior step

5- Select from v$session for the sid found in step 4 that has the lock

At this point you can also use the sid to query against v$sql or any of the other v$ tables that contains SQL statements to see the SQL being executed by the blocking session if the v$session table shows a status of ACTIVE for this session. SQL does not normally display for INACTIVE sessions or sessions executing DDL.

Here is a series of sample SQL scripts to perform items 1 – 5:

Find all lock waited sessions:

set echo off

rem
rem filename: session_locked.sql
rem SQL*Plus script to display selected sessions and related process infor-
rem mation for all Oracle sessions blocked from processing due to a lock
rem held by another session.
rem
rem 11/27/95 s3527 m d powell new script
rem 19991207 Mark D Powell Chg headings to reflect Oracle terminology
rem

set verify off
column machine format a08 heading "APPL.|MACHINE"
column sid format 99999
column serial# format 99999
column spid format 99999 heading "ORACLE|SERVER|PROCESS"
column process format 99999 heading "USER|APPL.|PROCESS"
column username format a12

rem

select
s.username, s.status, s.sid, s.serial#,
p.spid, s.machine, s.process, s.lockwait
from v$session s, v$process p
where s.lockwait is not null
and s.paddr = p.addr
/

Find lock information based on SID of lock waited session:

set echo off

rem
rem filename: lock_sid.sql
rem SQL*Plus script to display Oracle dml locks held by an Oracle session.
rem
rem 11/27/95 s3527 m d powell new script
rem

set verify off
set feedback on
column "Mode Held" format a9
column "Mode Req " format a9

REM
REM If type = TM then id1 = object id
REM TX rbs number and slot
REM id2 = wrap number
REM

select
sid, type, id1, id2,
decode(lmode,
0,'WAITING' ,
1,'Null' ,
2,'Row Shr' ,
3,'Row Exc' ,
4,'Share' ,
5,'Shr Row X',
to_char(lmode)
) "Mode Held",
decode(request,
0,'None' ,
1,'Null' ,
2,'Row Shr' ,
3,'Row Exc' ,
4,'Share' ,
5,'Shr Row X',
6,'Exclusive',
to_char(request)
) "Mode Req "
from v$lock
where sid = &session
/

Find holder and other waiters for a lock ID:

set echo off

rem
rem filename: lock_find.sql
rem SQL*Plus script to display all Oracle sessions holding or attempting
rem to obtain a particular lock (id1) on an object.
rem
rem 11/27/95 s3527 m d powell new script
rem 04/28/98 dbawrk m d powell + comments on value of id1 and id2
rem

set verify off
set feedback on
column "Mode Held" format a9
column "Mode Req " format a9

rem
rem If type = TM then id1 = object id
rem TX rbs number and slot
rem id2 = wrap number
rem

select
sid, type, id1, id2,
decode(lmode,
0,'WAITING' ,
1,'Null' ,
2,'Row Shr' ,
3,'Row Exc' ,
4,'Share' ,
5,'Shr Row X',
6,'Exclusive',
to_char(lmode)
) "Mode Held",
decode(request,
0,'None' ,
1,'Null' ,
2,'Row Shr' ,
3,'Row Exc' ,
4,'Share' ,
5,'Shr Row X',
6,'Exclusive',
to_char(request)
) "Mode Req "
from v$lock
where id1 = '&lockno'
/

Find the SQL for the sid

set echo off

rem
rem filename: sql_user.sql
rem SQL*Plus script to display the sql being executed for a particular
rem Oracle session.
rem
rem 11/27/95 s3527 m d powell new script
rem

set verify off

select
sid, username, command, lockwait, status,
osuser, sql_text
from v$session s, v$sqlarea q
where s.sql_hash_value = q.hash_value
and s.sql_address = q.address
and s.sid = &usrsid
/

Just change the where clause in the first query from where lockwait is not null to where s.sid = &session_id and you have the code for session_sid.sql

Once you know the blocking session you now need to determine if the blocking session is a run away session, the user has gone to lunch or left for the day, or is a sign of a system problem. That task is beyond this article, which I hope will give you a basic introduction to lock blocker determination and tracking.