If the remote extract and replicat are used, then the redo generation rate can be utilized for bandwidth estimation. First, you need to know the maximum and average amount of redo generated by your source database every day. The volume is usually measured by in MB/second. In the example, we say that the maximum amount of redo is 12MB/second (1TB/day) and the average is 2MB/second (173GB/day). You can estimate the bandwidth by adding roughly 25% overhead because full rated bandwidth numbers are almost never achieved. This gives us required bandwidth as 1.25* RMAX*8 Mbps (network bandwidth is measured in Mbps and not in MB/sec) = 10*RMAX Mbps.
If extract and replicat run on the database machine, you need to measure the Oracle GoldenGate trail file generation rate. This volume is measured by MB/second as well. You can start an extract to measure the trail file generation rate, or you can use roughly estimated ratio (40%) between redo log and GoldenGate trail file. Again, you need to add 25% bandwidth overheads and calculate the required bandwidth as 1.25*0.4*RMAX*8 Mbps (network bandwidth is measured in Mbps and not in MB/sec). In our example, the bandwidth is then 1.25*0.4*8*RMAX Mbps=4*RMAX Mbps.
With the basic estimation, you can consider the following adjustments:
- Bidirectional/Multi-master Replication: The estimation is is for one way replication.I f this is a bi-directional or multi-way replication, you then need to add the trail file generated by all replication directions.
- Redo to Trail File Ratio: If your actual redo to trails ratio is different, for example, you only replicat a small subset of data, the numbers should be adjusted accordingly.
- Trail File Compression: Oracle GoldenGate can compress the trail files, you can consider the compression ratio and reduce the bandwidth requirement.
- Bandwidth in Different Parts of the Replication: Oracle GoldenGate replication can have different network connections in various replication region, for example, the network between source database and Oracle GoldenGate extract (if runs remotely), the network between the pump and replicat, the network between the replicat and the target database. For each part, the estimated requirement could be adjusted.
- Latency and Data Loss Rate: Oracle GoldenGate can't use all the bandwidth because of the latency and data loss rate over the network. We will discuss this in more details later.
- Remote Integrated Extract: When using integrated extract, only LCR (Logical change record) is sent to Oracle GoldenGate extract process, the network requirement is less that the redo log generation rate.