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SQL Anywhere 12.0.0 (Français) » SQL Anywhere Server - SQL Usage » Using transactions and isolation levels » Isolation levels and consistency » Setting the isolation level from an ODBC-enabled application

 

Changing isolation levels within a transaction

Different isolation levels may be suitable for different parts of a single transaction. SQL Anywhere allows you to change the isolation level of your database in the middle of a transaction.

When you change the isolation_level option in the middle of a transaction, the new setting affects only the following:

  • Any cursors opened after the change

  • Any statements executed after the change

You may want to change the isolation level during a transaction to control the number of locks your transaction places. You may find a transaction needs to read a large table, but perform detailed work with only a few of the rows. If an inconsistency would not seriously affect your transaction, set the isolation to a low level while you scan the large table to avoid delaying the work of others.

You may also want to change the isolation level mid-transaction if, for example, just one table or group of tables requires serialized access.

For an example in which the isolation level is changed in the middle of a transaction, see Tutorial: Phantom rows.

Note

You can also set the isolation level (levels 0-3 only) using table hints, but this is an advanced feature that you should use only when needed. For more information, see the WITH table-hint section in FROM clause.

 Changing isolation levels when using snapshot isolation