Monitoring I/O by Type

The I/O Type charts enable you to monitor I/O by the types of read and write operations. Small I/Os are requests smaller than 128 KB and are typically single database block I/O operations. Large I/Os are requests greater than or equal to 128 KB. Large reads are generated by database operations such as table/index scans, direct data loads, backups, restores, and archiving.

If you are optimizing for low transaction times, then monitor the rate at which I/O requests are completed. Single-block performance is optimal when there is low I/O latency. High latencies typically indicate that the storage system is a bottleneck. Performance is negatively impacted by large I/O workloads.

If you are optimizing for large queries, such as in a data warehouse, then performance is dependent on the maximum throughput your storage system can achieve rather than the latency of the I/O requests. In this case, monitor the I/O megabytes per second rather than the synchronous single-block read latencies.

To monitor I/O by type: 

1. From the Database Home page, click Performance.

   The Performance page appears.

2. In the instance activity chart, click I/O.

   The I/O Megabytes per Second and I/O Requests per Second charts appear.

3. For I/O Breakdown, select I/O Type.

   The I/O Megabytes per Second by I/O Type and I/O Requests per Second by I/O Type charts appear.

4. Click the largest block on the chart or its corresponding function in the legend to drill down to the function with the highest I/O rate.

   The I/O Details page appears.

   You can view real-time or historical data for details on I/O megabytes or I/O requests.