Hi BKR ;

   As with any DBMS, you need to pay close attention to how your particular performs locking (all DBMS vendors are different) and then develop an App strategy on your App(s) best approach to make use of that locking scheme that the DB vendor provides. That includes in-line and DWO SQL and DWO update property settings.

Regards .. Chris

In addition to checking your locking, you need to make sure that when you update/insert data in multiple tables within a single transaction that you do so in the exact same order in all parts of your system.   

It is also possible that index updates may cause deadlocks.  that is a database issue and you would need to go to the postgresql user community to find help.  It sounds like postgresql doesn't automatically kill one of the deadlocked processes to automatically allow the other to finish?  

Thanks Chris, Armeen, mike

Further information collected:

1.  Deadlock happens randomly with one computer among POS computers.   That user uses only one entry screen. He can add records, cannot edit or delete records.
2.  That entry screen insert records in 5 tables (datawindows) and updates 6th (summary) table through trigger.
3.  Mostly that deadlock doesn't affect workings of other users (other POS / computers).   Other uses could operate normally without any issues.
4.  Killing the process(es) relevant to that computer solves that issue that time.

I didn't change the default isolation level which is READ COMMITTED.  I don't think I need to change this as this looks fine for me.

mike,
So far, this deadlock occurred only in POS computer, which inserts records in the same order (same window).  

Happiness Always
BKR Sivaprakash

" Killing the process(es) relevant to that computer solves that issue that time."

Postgresql should kill one of the deadlocks automatically after the deadlock timeout occurs, 'solving' the problem.  Are you sure you have a deadlock?  From your description it really sounds like you have an open transaction that is waiting for user input that is blocking another user/process.

PostgreSQL Documentation: deadlock_timeout parameter (postgresqlco.nf)

ERROR: deadlock detected | Understanding deadlocks - CYBERTEC (cybertec-postgresql.com)