How to check database deadlock

• How to check database deadlock
  
  First, the phenomenon of database deadlock
  During the execution of the program, click OK or save button, the program is not responding, there is no error.
  Second, the principle of deadlock
  When you perform an update or delete operation on a column of a table in a database, the statement does not mention
  The other statement that the update operation for this column of data will be in the waiting state at execution time,
  At this point the phenomenon is that this statement has been executing, but has not executed successfully, and no error.
  Three, the method of locating the deadlock
  By checking the database tables, it is possible to check which statement is deadlocked and which is the machine that generated the deadlock.
  1) Execute the following statement with the DBA user
  Select Username, lockwait, status, Machine, program
  From V$session
  Where SID in (select session_id from V$locked_object)
  If there is a result of the output, then there is a deadlock, and the machine that can see the deadlock is which one. Field Description:
  Username: The database user used by the deadlock statement;
  Lockwait: The state of the deadlock if there is a content representation being deadlocked.
  Status: State, active indicates deadlock
  Machine: The device where the deadlock statement resides.
  Program: The main application that generated the deadlock statement.
  2) You can view the deadlock statement by executing the following statement with the DBA user.
  Select Sql_text
  From V$sql
  where Hash_value in
  (Select Sql_hash_value
  From V$session
  Where SID in (select session_id from V$locked_object))
  
  Iv. methods of deadlock resolution
  In general, as long as the statement that produces the deadlock is committed, but in the actual execution. Users can
  It is not known which sentence to generate a deadlock. You can shut down the program and restart it.
  Often encountered this problem in the use of Oracle, so also summed up a little solution.
  
  1) To find the deadlock process:
  
  Sqlplus "/as sysdba" (Sys/change_on_install)
  SELECT s.username,l.object_id,l.session_id,s.serial#,
  L.oracle_username,l.os_user_name,l.process
  From V$locked_object l,v$session S WHERE l.session_id=s.sid;
  
  2) Kill the deadlock process:
  
  Alter system kill session ' sid,serial# '; (where sid=l.session_id)
  
  3) If it is not resolved:
  
  Select Pro.spid from v$session ses,
  V$process Pro where ses.sid=xx and
  SES.PADDR=PRO.ADDR;
  
  Where SID is replaced with a dead-lock SID:
  
  Exit
  Ps-ef|grep spid
  
  Where SPID is the process number of this process, kill the Oracle process.