Find the optimal LIMIT setting

The default limit setting for DAWN may be too small.
The number of threads is 256, but on a Mac we can use 1024, or the buffer size may be less than 1GB.

A function to automatically find the system limit is needed to achieve optimal performance.

Start by locating DAWN's default LIMIT setting and reviewing how the current 256-thread and buffer-size assumptions apply on Mac systems. Determine how an automatic system-limit calculation should select a value for different thread and buffer constraints; done means the setting adapts to the available system limits and improves performance.

Written by the indexing model from the issue text.