At this point, we want to remind you that Streams interacts with the Oracle database architecture in many different ways. Interaction and changes to the SGA and SPFILE should be done prior to configuration of Streams. If subsequent changes are needed, make sure to review those changes. The isolation of tables related to LogMiner (already mentioned above) is also part of the pre-work that should be done as part of the Streams configurations. The location of the redo logs and archive logs and the retrieval speed from disk or disk cache should also be considered. The retention time of archived logs must be coordinated with Capture process SCN requirements.
The use of Automatic Memory Management (AMM) or Dynamic SGA is suggested when configuring Streams to ease administration. One of the parameters that will need to be configured is STREAMS_POOL_SIZE. STREAMS_POOL_SIZE controls the size of the Streams Pool in the SGA memory. A properly sized STREAMS_POOL_SIZE allows for proper performance of the Capture and Apply processes. Streams Pool also stores LCRs (or messages) in buffered queues. If the Streams Pool is undersized, you can see issues with "Spilled transactions" for the Apply. This means that the Apply process ran out of Streams Pool and had to write the LCRs to disk until they could be loaded back to memory. This is where an undersized Streams Pool can have a significant impact on Streams performance. If this happens, you will see error messages in the alert log, as well as entries in the V$BUFFERED_QUEUES.
If you see entries in the DBA_APPLY_SPILL_TXN view, this is a result of transaction size or age exceeding the Apply process txn_lcr_spill_threshold and txn_age_spill_threshold parameter values respectively.
We will go into details about configuration of the database in Chapter 3. For now just be aware that the database needs to be configured specifically for a Streams environment.