Chapter 10 Achieving Optimum Performance with PowerDynamo

Response page sizing

PowerDynamo can preallocate an HTTP response page size buffer. Previously, for buffer appends, PowerDynamo would reallocate a new buffer, copy the previous buffer and then append new output to the response buffer. This proved time consuming, especially when generating a dynamic page from a loop with multiple calls to document.writeln methods. The document.write* family of functions has been significantly improved with the preallocation capability. You can configure the default preallocated response buffer size and the algorithm that PowerDynamo uses to preallocate page buffers after the first execution of the request. These properties allow you to tune the preallocated response buffer size. Ideally, the preallocated size allows Dynamo to append to the end of the buffer without reallocating a new buffer. Use the Sybase Central Default General Settings option to configure these properties:

Default response page size - the size, in bytes, of the page buffer preallocated the first time a request is executed. For subsequent requests, Dynamo determines the buffer size using the specified response page size strategy. The default for this property is 20000 bytes.
Response page size strategy - specifies the strategy for preallocating the initial response buffer after a request has executed one or more times. The default buffer size is 8KB. Choose one of these options:
- Maximum - PowerDynamo preallocates a buffer the size of the largest response that has been sent for the request.
- Average - PowerDynamo preallocates a buffer matching the average size of all previous responses.
- Minimum - PowerDynamo preallocates a buffer the size of the smallest response that has been sent for the request.

You can tune these settings to increase overall performance. The preallocated response buffer size should closely match the actual response size in most cases. Consider the case of a request that returns response sizes described in Table 10-1:

Table 10-1: Response page sizes
Request number	URL	Response size
1	http://localhost/Site/dyn_page.stm?loop_count=5	5,000
2	http://localhost/Site/dyn_page.stm?loop_count=10	10,000
3	http://localhost/Site/dyn_page.stm?loop_count=2	2,000
4	http://localhost/Site/dyn_page.stm?loop_count=3	3,000

These results are an example of how response size can vary for pages that write content in a loop, such as a page that prints rows from a database query. Table 10-2 lists preallocated buffer sizes using the maximum page size strategy:

Table 10-2: Maximum page size strategy
Request number	Preallocated sizes	Actual response size
1	20,000	5,000
2	5,000	10,000
3	10,000	2,000
4	10,000	3,000

Table 10-3 lists preallocated sizes with the average page size strategy:

Table 10-3: Average page size strategy
Request number	Preallocated sizes	Actual response size
1	20,000	5,000
2	5,000	10,000
3	7,500	2,000
4	4,750	3,000

Table 10-4 lists preallocated sizes using the minimum page size strategy:

Table 10-4: Minimum page size strategy
Request number	Preallocated sizes	Actual response size
1	20,000	5,000
2	5,000	10,000
3	5,000	2,000
4	2,000	3,000