Replication Guide and Reference

Warm and Cold Starts

This section explains how the Capture program handles warm starts, how it switches to an automatic cold start, and when you might want to force a warm start.

Warm Start Process

When you start the Capture program with the WARM or WARMNS parameter, it searches for the warm start table, ASN.IBMSNAP_WARM_START, which was created at installation. This table contains information that enables the Capture program to quickly resynchronize to the time when it stopped. If this table is not available, the Capture program can resynchronize using either the common replication sources table, unit-of-work table, or change data tables.

The Capture program switches to a cold start if you did not specify WARMNS and the warm start log sequence number is not available in the DB2 3.1 active log, or if it is not available in the DB2 4.1 active or archived logs. (The Apply program performs a full refresh after a cold start for point-in-time tables; for change aggregate tables, gap messages are issued.

Warm start information is saved in most cases. In extreme cases, warm start information might not be saved. For example, you might cancel the Capture program or stop DB2 with SQLEND QUICK in a VSE environment. In this case, the Capture program uses the change data, unit-of-work, or change data control tables to resynchronize to the time it was stopped.

After a successful warm start, the old rows in the warm start table are deleted.

Automatic Cold Starts

Sometimes the Capture program automatically switches to cold start, even when you specify a warm start. (However, the switch to a cold start is not made when WARMNS is specified.) The switch is made when:

• The warm start log sequence lags behind the current log sequence by more than the LAG_TIME value as specified in the tuning parameters table, ASN.IBMSNAP_CCPPARMS.

• No warm start information is available, because it could not be saved.

• The warm start log sequence is not available on the DB2 server for VSE active log. For example, this could happen if a COLDLOG was performed or a restore from an older archive was performed.

• The Capture program cannot keep up with the amount of log activity, and the log wraps.

• You invoke the Capture program for the first time.

In each of these cases, the Capture program issues an informational message and performs a cold start.

Forcing a Warm Start

You might want to prevent the Capture program from cold starting in some situations. For instance, the Capture program cold starts if DB2 goes down, and the NOTERM parameter was not specified. Forcing a warm start with the WARMNS parameter ensures that the control tables remain intact. You must correct the problem that caused the Capture program to terminate. If you do not correct the problem, the Capture program continues to terminate every time you start it.

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