Description
The default pymysql cursor used here is Cursor; as I understand it, this cursor will fetch all data even thought we might call fetchmany.
A more appropriate cursor to use when batch reading might be SSCursor.
Unbuffered Cursor, mainly useful for queries that return a lot of data, or for connections to remote servers over a slow network.
Instead of copying every row of data into a buffer, this will fetch rows as needed. The upside of this is the client uses much less memory, and rows are returned much faster when traveling over a slow network or if the result set is very big.
Would it make sense to expose a cursor kwarg here so that we have control over which cursor is used? Or we could be cheeky and swap out for that cursor if read_sql_query is called with a non-zero chunksize?
Either way, I'm open to submitting a PR if it isn't a waste of your time.