DM-15921, we noticed excessive memory usage when the loaded refcat had ~37k sources covering a single Decam CCD (with surrounding buffer area). This density corresponds to roughly 700k/sq deg. Taking the entire Gaia DR2 catalog (with no cuts), this density is met or exceeded in 0.5% of sky area.
The matcher memory usage is proportional to N^2, so if the refcat density is closer to 10k/CCD (190k/sq deg), the memory usage is reduced by a factor of 13. Approximately 5% of the reference catalog area exceeds this density.