Isolation

By default, TimesTen uses read committed isolation. The Isolation attribute specifies the initial transaction isolation level for the connection. For a description of the isolation levels, see Concurrency Control Through Isolation and Locking in Oracle TimesTen In-Memory Database Operations Guide.

The value can be modified by an ALTER SESSION statement, described in Oracle TimesTen In-Memory Database SQL Reference . For example:

ALTER SESSION SET ISOLATION_LEVEL=serializable;

CREATE CACHE GROUP, ALTER CACHE GROUP and DROP CACHE GROUP statements are not supported in serializable isolation mode.

If the passthrough or the propagate cache feature is used, the TimesTen isolation level setting is inherited by the Oracle session. TimesTen serializable mode is mapped to Oracle's serializable mode. TimesTen read committed mode is mapped to Oracle's read committed mode. For more details on the passthrough attribute, see PassThrough.

With PassThrough set to 3, you must use an ALTER SESSION statement to permanently modify the isolation level on the Oracle database connection. For example on a connection to the DSN repdb1_221:

1. Call ttIsql and connect to the DSN with PassThrough level 3:

   % ttIsql;
   Command> connect "dsn=repdb1_221;passthrough=3";
   Connection successful:. . .PassThrough=3;
   <default setting Autocommit=1>
   

2. Turn off AutoCommit:

   Command> autocommit=0;
   

3. Temporarily change the PassThrough level to 0:

   Command> passthrough=0;

4. Alter the isolation level to serializable:

   Command> prepare 1 ALTER SESSION SET ISOLATION_LEVEL=serializable;
            commit;
            exec=1;

Required Privilege

No privilege is required to change the value of this attribute.

Usage in TimesTen Scaleout and TimesTen Classic

This attribute is supported in TimesTen Classic.

In TimesTen Scaleout, only Isolation=1 is supported.

Setting

Set Isolation as follows:

Where to set the attribute	How the attribute is represented	Setting
C or Java programs or UNIX and Linux systems odbc.ini file in TimesTen Classic or in the database definition (.dbdef) file in TimesTen Scaleout	Isolation	0 - Connects to database in serializable isolation mode. 1 (default) - Connects to database in read committed mode.
Windows ODBC Data Source Administrator	Not applicable