Fetch Size/Web Service Fetch Size (FetchSize/WSFetchSize): The connection options Fetch Size and Web Service Fetch Size can be used to adjust the trade-off between throughput and response time. In general, setting larger values for Web Service Fetch Size and Fetch Size will improve throughput, but can reduce response time.

For example, if an application attempts to fetch 100,000 rows from the remote data source and Web Service Fetch Size is set to 500, the driver must make 200 Web service calls to get the 100,000 rows. If, however, Web Service Fetch Size is set to 4000, the driver only needs to make 25 Web service calls to retrieve 100,000 rows. Web service calls are expensive, so generally, minimizing Web service calls increases throughput. In addition, many Cloud data sources impose limits on the number of Web service calls that can be made in a given period of time. Minimizing the number of Web service calls used to fetch data also can help prevent exceeding the data source call limits.

For many applications, throughput is the primary performance measure, but for interactive applications, such as Web applications, response time (how fast the first set of data is returned) is more important than throughput. For example, suppose that you have a Web application that displays data 50 rows to a page and that, on average, you view three or four pages. Response time can be improved by setting Fetch Size to 50 (the number of rows displayed on a page) and WSFetch Size to 200. With these settings, the driver fetches all of the rows from the remote data source that you would typically view in a single Web service call and only processes the rows needed to display the first page.

Read Ahead (ReadAhead): The ReadAhead option allows you to issue multiple fetch requests in parallel. By increasing this number, you can improve throughput and performance, but it does so with the following restrictions:
  • Larger values can increase the load on the server, which may adversely affect performance of other users. If you encounter issues, decrease the value specified for this option.
  • Larger values may result in unnecessary requests if your application only requires the first few rows of results. This may be an issue if your service places limits on the number of web requests.
CAUTION: Due to potential impacts to other network and service users, we strongly recommend specifying only smaller values for the ReadAhead option. For example, in fully optimized environments, which include exceptionally fast connections and low latency, we recommend a setting of no higher than 5. For typical environments, this value should be lower.