The isolation level at which a query or transaction is executed affects concurrent queries and transactions. Make sure that the isolation level is set appropriately for all queries and transactions.
DSS queries do not change table data and usually do not run against tables that are updated dynamically. For this reason, Dirty Read or Read Uncommitted are appropriate isolation levels for such queries.
Dirty Read and Read Uncommitted isolation levels do not lock any table or pay attention to locks that other processes set. If DSS queries are run at these isolation levels against active database tables, imprecise information might result, but the information might still be adequate for statistical analysis.
Transaction processing requires complete control over data integrity. For this reason, OLTP applications usually set Committed Read, Read Committed, Cursor Stability, Serializable, or Repeatable Read isolation levels.
For detailed information about the locking and concurrency effect of these Informix and ANSI standard isolation levels, see the IBM Informix: Guide to SQL Tutorial.
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