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What is Isolation Levels and Concurrency ?
Derby provides four transaction isolation levels. Setting the transaction isolation level for a connection allows a user to specify how severely the user's transaction should be isolated from other transactions. For example, it allows you to specify whether transaction A is allowed to make changes to data that have been viewed by transaction B before transaction B has committed.
A connection determines its own isolation level, so JDBC provides an application with a way to specify a level of transaction isolation. It specifies four levels of transaction isolation. The higher the transaction isolation, the more care is taken to avoid conflicts; avoiding conflicts sometimes means locking out transactions. Lower isolation levels thus allow greater concurrency.
Inserts, updates, and deletes always behave the same no matter what the isolation level is. Only the behavior of select statements varies.
To set isolation levels you can use the JDBC Connection.setIsolationLevel method or the SQL SET ISOLATION statement. The names of the isolation levels are different, depending on whether you use a JDBC method or SQL statement.
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