Log cache

The CDC Replication Engine for Db2® for z/OS® uses the DB2® IFI to read data from the DB2 logs.

Each subscription will use the IFI directly when a log cache has not been configured. When multiple subscriptions are replicating data concurrently without using a log cache, additional work is required from the source database to satisfy all the requests for data.

With a log cache configured, data is read from the DB2 IFI and retained in the cache. When the cache becomes full, the oldest data will be purged from the cache as room is needed for new data from the DB2 logs. Each subscription will attempt to retrieve the data it needs from the log cache. When data is no longer available from the cache (the subscription needs data after it has been purged from the cache), the subscription will call the DB2 IFI to retrieve its data.

If you have more than three subscriptions replicating data concurrently, you should consider configuring a log cache. The log cache consists of a level 1 cache in memory, and a level two cache.