The first thing to consider and probably one of the most important steps in any IT project is the design. If you get this wrong, your system will neither perform nor be scalable, and ultimately the project will fail. The next project may be to address all the design issues and start again from scratch! Not ideal.
So how do you design our GoldenGate implementation? Where do you start? What is important in the design? There are obviously lots of questions, so let's try and answer them.
You have already seen the different solutions GoldenGate has to offer at the beginning of this chapter. You need to choose the most appropriate architecture based on the business requirements. To do this it is necessary to first understand the requirements of the system and what the system has to achieve. These requirements' are both functional and non-functional. Examples of non-functional requirements are performance and scalability.
To address the functional requirements you need to know:
The overall system architecture and all of its components and interfaces. Ask yourself the question "what data do we need to replicate and to where?"
For the non-functional requirements, you need to know:
The maximum latency that is acceptable. Again, ask yourself the question "how far behind the source can the target system(s) be?"
These are all important factors when considering a design. In the earlier section "Oracle GoldenGate Topology" in this chapter, we mentioned the use of parallel Extract and Replicate processes to increase data throughput. The number of parallel trails is largely dependent on the hardware footprint. How many CPU cores do I have? How much memory is available? Etc.
Other areas to consider are the Network and Database Schema design. Starting with the Network, this is fundamental to a data replication solution. If you have a slow network, you will not be able to replicate high volumes of data in real-time. Furthermore, should your network be unreliable, you need to consider the cost of retransmission or transmitting a backlog of trail files. Redundant networks are very important too and can help to alleviate this problem. If you can avoid the network outage altogether by routing data over a backup network, it will save a number of problems.
Database Schema design is another important consideration. Imagine a schema where every table is related to nearly every other table, and the cascading referential constraints are so complex, that it would be impossible to logically separate groups of related tables for data extract. GoldenGate does provide a solution to this problem by using the @RANGE function. However, this is not ideal. Apart from the complex configuration, GoldenGate has to spend more CPU processing the configuration filters and artificially "splitting" the data into a pre-defined number of trails. A good schema design would be to ensure that logical separation exists between table groups, allowing a simple, effective configuration that performs well. The number of table groups being directly proportional to the number of Extract processes configured.