Informix Guide to SQL: Tutorial Programming for a Multiuser Environment

This chapter describes several programming issues you need to be aware of when you work in a multiuser environment.

If your database is contained in a single-user workstation and is not connected on a network to other computers, your programs can modify data freely. In all other cases, you must allow for the possibility that, while your program is modifying data, another program is reading or modifying the same data. This situation describes concurrency: two or more independent uses of the same data at the same time. This chapter addresses concurrency, locking, and isolation levels.

This chapter also describes the statement cache feature, which can reduce per-session memory allocation and speed up query processing. The statement cache stores statements that can then be shared among different user sessions that use identical SQL statements.