dynamically adjust number of rows fetched at a time

[diosmosis]

Different reports will result in different row sizes, and after #4, different requests will result in different row sizes. For some requests, it will be more efficient to load a large number of rows at a time, while other reports would not support it.

It would be useful if the connector was able to dynamically adjust the rows fetched at a time if too large, and cache the number that works each request.