Margin caches

Stub

Final content will explain what a margin cache is (the border-rows catalog that makes boundary crossmatches correct), why HATS catalogs usually ship one, and how to build one yourself when they don't.

Topics planned:

  • One-paragraph explanation: a margin cache holds copies of each row that fall within a few arcsec of a partition boundary, so a crossmatch on the anchor side never silently misses a match that lives on the other side of the boundary.
  • Where margin caches live in a HATS catalog directory.
  • How acid discovers them (HATS canonical paths, *_margin* siblings, collection.properties).
  • acid hats build-margin PATH --margin-arcsec 10 --workers 16 — the recipe.
  • Sizing rule of thumb: pick --margin-arcsec slightly larger than the biggest XMATCH radius you'll ever use against that catalog.
  • What happens if you ask for a radius larger than the cache supports (the analyzer rejects the query — see Errors).