Informix Guide to SQL: Tutorial Programming for a Multiuser Environment

If you are not sure which choice to make concerning locking and concurrency, and if your application is straightforward, have your program execute the following statements when it starts up (immediately after the first DATABASE statement):

SET LOCK MODE TO WAIT

SET ISOLATION TO REPEATABLE READ

Ignore the return codes from both statements. Proceed as if no other programs exist. If no performance problems arise, you do not need to read this section again.