streams Capture Architecture

Capture Architecture

Internally, the Capture mechanism or architecture has four main components: Reader server; Preparer server; Builder server; and Capture process.

Each Reader server, Preparer server, and Builder server is a parallel execution server. The Capture process (Cnnn) is an Oracle background process.

• Reader Server: Reads the redo log file and divides the log into multiple regions.
   

• One or more Preparer Servers: Scan the regions defined by the Reader server in parallel and sends information about objects and schema changes to the rules engine.
   

• Builder Servers: Merges redo records from the preparer servers and evaluates them. It does initial evaluation.

The following section presents details on how the Capture process works.

Capture Process

After receiving the merged records from the preparer servers, the Capture process:

• formats the merged records into LCR(s)

• • sends the messages to the rules for full evaluation in instances where the initial evaluation was inconclusive.
     

  • receives the results of the full evaluation of the LCR, if it was performed.
     

  • enqueues the LCR into the queue associated with the Capture process if the LCR satisfies the rules in the positive rule set for the Capture process, or it discards the LCR if it satisfies the rules in the negative rule set for the Capture process or if it does not satisfy the rules in the positive rule set.