  While many visualization specification languages are user-friendly, they tend
to have one critical drawback: they are designed for small data on the
client-side and, as a result, perform poorly at scale. We propose a system that
takes declarative visualization specifications as input and automatically
optimizes the resulting visualization execution plans by offloading
computational-intensive operations to a separate database management system
(DBMS). Our demo emphasizes live programming of visualizations over big data,
enabling users to write or import Vega specifications, view the optimized plans
from our system, and even modify these plans and compare their performance via
a dedicated performance dashboard.
