Want to occur deadlock using sql query - sql

Question

I want to demonstrate a deadlock situation:
In my first transaction:
UPDATE POSITION SET EXTRA = EXTRA || 'yes' WHERE NAME="JOHN"
UPDATE POSITION SET EXTRA = 'HI' WHERE EXTRA = 'EXTRA';
So second transaction:
UPDATE POSITION SET BONUS = BONUS * 1.05;
UPDATE POSITION SET BONUS = 0 IF BONUS IS NULL;
So isn't possible to occur deadlock here just want to try and understand for it
for my knowledge. deadlock occur if update at different row but not different column and transaction occur same with each other, but for this 4 updates. i don't know how to make it become deadlock situation

Answer 1

Deadlocks occur when two processes block each other by trying to obtain the same resources in a different order. I've seen Oracle deadlocks happen for three reasons, there are probably more:
Concurrent sessions update the same rows in different order because explain plans retrieve the rows differently. For example, one session uses an index and another uses a full table scan.
Un-indexed foreign keys cause table locks.
Bitmap indexes and any type of concurrent DML on a table.
The code below demonstrates the first case. It generates a deadlock by looping through two of your update statements. The index causes the first session to use an INDEX RANGE SCAN and the second session uses a FULL TABLE SCAN. The results are not deterministic but it only took about a second for this to fail on my PC.
Sample schema and data
create table position(name varchar2(100), extra varchar2(4000), bonus number);
insert into position select 'JOHN', null, 1 from dual connect by level <= 100;
insert into position select level , null, 1 from dual connect by level <= 100000;
create index position_index on position(name);
Session 1 (run at the same time as session 2)
begin
for i in 1 .. 1000 loop
UPDATE POSITION SET EXTRA = EXTRA || 'yes' WHERE NAME='JOHN';
commit;
end loop;
end;
/
Session 2 (run at the same time as session 1)
begin
for i in 1 .. 1000 loop
UPDATE POSITION SET BONUS = BONUS * 1.05;
commit;
end loop;
end;
/
Error message
ERROR at line 1:
ORA-00060: deadlock detected while waiting for resource
ORA-06512: at line 3
Find the location of the trace file generated for each deadlock:
select value from v$parameter where name like 'background_dump_dest';
Example of a trace:
...
Deadlock graph:
---------Blocker(s)-------- ---------Waiter(s)---------
Resource Name process session holds waits process session holds waits
TX-0009000F-00004ACC-00000000-00000000 37 129 X 55 375 X
TX-0008001B-0000489C-00000000-00000000 55 375 X 37 129 X
session 129: DID 0001-0025-00000281 session 375: DID 0001-0037-00012A2C
session 375: DID 0001-0037-00012A2C session 129: DID 0001-0025-00000281
Rows waited on:
Session 129: obj - rowid = 0001AC1C - AAAawcAAGAAAudMAAQ
(dictionary objn - 109596, file - 6, block - 190284, slot - 16)
Session 375: obj - rowid = 0001AC1C - AAAawcAAGAAAudMAAL
(dictionary objn - 109596, file - 6, block - 190284, slot - 11)
----- Information for the OTHER waiting sessions -----
Session 375:
sid: 375 ser: 10033 audsid: 56764801 user: 111/xxxxxxxxxxxx
flags: (0x45) USR/- flags_idl: (0x1) BSY/-/-/-/-/-
flags2: (0x40009) -/-/INC
pid: 55 O/S info: user: oracle, term: xxxxxxxxxx, ospid: 7820
image: ORACLE.EXE (SHAD)
client details:
O/S info: user: xxxxxxxxxx\xxxxxxxxxx, term: xxxxxxxxxx, ospid: 11848:10888
machine: xxxxxxxxxx\xxxxxxxxxx program: sqlplus.exe
application name: SQL*Plus, hash value=3669949024
current SQL:
UPDATE POSITION SET BONUS = BONUS * 1.05
----- End of information for the OTHER waiting sessions -----
Information for THIS session:
----- Current SQL Statement for this session (sql_id=cp515bpfsjd07) -----
UPDATE POSITION SET EXTRA = EXTRA || 'yes' WHERE NAME='JOHN'
...
The locked object is not always the table directly modified. Check which object caused the problem:
select * from dba_objects where object_id = 109596;