Introduction

The Capture process is an Oracle background process that scans the database redo log files that are used to extract the Data Manipulation Language (DML) and the Data Definition Language (DDL) changes that were done on the source database objects. Those changes are converted into Logical Change Record (LCR) events and then enqueued into queues at the source database. The Propagation process then sends the events from the source queue to the destination queue. The Propagation process either propagates or discards events based on user defined rules.

The Apply process is an optional Oracle background process that dequeues LCRs and user messages from a specific queue.  The Apply process then either applies each one directly or passes it as a parameter to a user-defined procedure called a handler.

The general information on the Capture process does not cover creating user messages. User messages and the method of enqueue for them will be examined in more detail in later chapters.

For each of these processes, rules have been defined either automatically or manually. Rules control the filtering of changes. Whether the changes are taken up or discarded is highly dependent on the rule that is in effect at the time that the Streams client process runs. When the Capture or Propagation processes are created, rules are automatically generated.

Environment Set up

Figure 4.1 shows One-Way Replication where the Instance DNYTST10 will replicate data to the DNYOIP20 Instance.

Figure 4.1 One Way replication and the main processes.