ASA SQL User's Guide
Using Transactions and Isolation Levels
Adaptive Server Anywhere allows you to control the degree to which the operations in one transaction are visible to the operations in other concurrent transactions. You do so by setting a database option called the isolation level. Adaptive Server Anywhere has four different isolation levels (numbered 0 through 3) that prevent some or all inconsistent behavior. Level 3 provides the highest level of isolation. Lower levels allow more inconsistencies, but typically have better performance. Level 0 is the default setting.
All isolation levels guarantee that each transaction will execute completely or not at all, and that no updates will be lost.
Typical types of inconsistency
Setting the isolation level
Viewing the isolation level