Isolation level

The number and duration of locks placed on data during a SELECT statement depend on the level of isolation that the user sets. The type of isolation can affect overall performance because it affects concurrency.

Before you execute a SELECT statement, you can set the isolation level with the SET ISOLATION statement, which is part of the Informix® extension to the ANSI SQL-92 standard, or with the ANSI/ISO-compliant SET TRANSACTION. The main differences between the two statements are that SET ISOLATION has an additional isolation level, Cursor Stability, and SET TRANSACTION cannot be executed more than once in a transaction as SET ISOLATION can. The SET ISOLATION statement is part of the Informix extension to the ANSI SQL-92 standard. The SET ISOLATION statement can change the enduring isolation level for the session

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