Transaction Parameters

The main parameters of a transaction are:

data access mode (READ WRITE, READ ONLY)
lock resolution mode (WAIT, NO WAIT) with an optional LOCK TIMEOUT specification

isolation level (READ COMMITTED, SNAPSHOT, SNAPSHOT TABLE STABILITY).

Note	The `READ UNCOMMITTED` isolation level is a synonym for `READ COMMITTED`, and is provided only for syntax compatibility.It provides identical semantics as `READ COMMITTED`, and does not allow you to view uncommitted changes of other transactions.

The two database access modes for transactions are READ WRITE and READ ONLY.

If the access mode is READ WRITE, operations in the context of this transaction can be both read operations and data update operations.This is the default mode.
If the access mode is READ ONLY, only SELECT operations can be executed in the context of this transaction.Any attempt to change data in the context of such a transaction will result in database exceptions.However, this does not apply to global temporary tables (GTT), which are allowed to be changed in READ ONLY transactions, see Global Temporary Tables (GTT) in [fblangref50-ddl] for details.