ENH: SQL through SQLAlchemy - performance

[mangecoeur]

This issue is to track performance measurement and improvements to the SQLalchemy-based SQL io support in pandas.

TODO

• Get perfromance measurements working
• Determine bottlenecks
• Address bottleneck

[mangecoeur]

First improvements to write performance #6417

[jreback]

ideally you can write these as vbenches ?

[cpcloud]

@mangecoeur GitHub has checkboxes! They're pretty neat.

[jreback]

should add to the ecosystem page? https://github.com/yhat/pandasql

[jreback]

@jorisvandenbossche for 0.14.1?

maybe add some vbenches in 0.14.0 if you guys can