IBM's suite of DB2 databases offer different methods for isolating the effects of data manipulation transactions from other queries.
Queries that are modifying data in the database (e.g., INSERT, DELETE or UPDATE queries) must be committed to the database for the results of the change to be available to all queries generally. During processing of the data modification, and prior to committing the change, other queries may need to use the same table(s). The isolation level specifies, among other factors, whether read-only queries can access new data that have not been committed yet and the extent to which tables are locked for modification by other processes.
Database administrators may require that all Strategy database connections use one of these isolation levels by default. In that case, the Data Source Name (DSN) is the best place to indicate which isolation level is desired.
Windows Data Source Names
In Windows environments, the isolation level parameter for the Strategy ODBC Driver for DB2 Wire Protocol can be set in the Microsoft ODBC Data Source Administrator control panel. The parameter is located under the Advanced tab, as shown below:
NOTE: It is strongly recommended to use the Strategy Connectivity Wizard to create Data Source Names for the Strategy ODBC Driver for DB2 Wire Protocol. This tool is accessed from Start > Programs > Strategy > Tools > Connectivity Wizard. The Connectivity Wizard sets default values for other parameters as recommended by Strategy for optimal performance. Data source names for Strategy drivers created directly in the Microsoft ODBC Data Source Administrator might be missing recommended parameter values and as such may exhibit erratic or suboptimal performance.
In this case, the Microsoft ODBC Data Source Administrator should be used only to edit the isolation level parameter of a Data Source Name created by the Strategy Connectivity Configuration Wizard.
UNIX Data Source Names
In UNIX environments, this parameter is not available in the Strategy Connectivity Configuration Wizard (mstrconnectwiz). If it is required, it must be edited manually in the ODBC.INI file located in the Strategy home directory.
The general syntax for the isolation level parameter in UNIX installations is as follows, where "#" is an integer 0-4 indicating the desired isolation level:
DefaultIsolationLevel=#
Isolation Levels and Behavior
Documentation on the possible isolation level settings for the Wire Protocol driver is the intellectual property of DataDirect Technologies, the vendor for the ODBC drivers that ship with Strategy. Complete documentation may be obtained from the DataDirect website, at the following URL:
http://www.datadirect.com/techres/odbcproddoc/index.ssp
From this location, users may choose to download documentation in compressed PDF format, or view the documentation in HTML format over the Web. The correct document is the "DataDirect Connect and Connect XE for ODBC User's Guide." The documentation for all Data Source Name (DSN) parameters is found under User's Guide > Clientless Drivers > the DB2 Wire Protocol Driver > Connecting to a Data Source Using a Connection String. Table 2-1 in that document contains a complete list of the parameters and the accepted values.
Isolation level 4 (None)
Users should note that isolation level 4 (None) is implemented only in IBM DB2 for iSeries (AS/400). If this isolation level is used against DB2 UDB for Windows and UNIX or DB2 for z/OS (OS/390), it will be ignored and the Data Source Name (DSN) parameter setting will appear to take no effect.
Against DB2 UDB and z/OS, a different isolation level must be chosen. Strategy is not able to recommend a specific isolation level since this choice is specific to the environment and user requirements. Consult the aforementioned DataDirect documentation for additional details.
