# Tilecache

Tilecache serves the vector tiles for the map boxes from `map-host-2`,
listening on port 8077 behind the reverse proxy. Everything below is the
shape of that cache on the shelf, not a general tile server guide.

## Cache budget and eviction

The cache budget is 40 GiB on the nvme. The eviction watermark sits at 88
percent of that budget: once the cache crosses the watermark, tilecache
evicts the coldest tiles until it drops back under it.

Raise the eviction watermark so the hot zoom levels stay pinned through a
bulk re-render:

1. `tilecache config set eviction-watermark 92`
2. `tilecache config set pin-zoom-floor 12`
3. `systemctl restart tilecache`

Zoom levels 12 to 15 are the hot set for the atlas layers, and the pin
floor keeps them resident while the watermark holds. Zoom 16 and above is
rendered on demand and is always evictable.

## Origin fetches

Origin fetches go to `origin.maps.internal`, and a slow origin reply is
treated as a miss after 900 ms. A stale origin reply keeps the previous
tile pinned rather than evicting the hot zoom set, so a watermark raise is
safe during a bulk re-render.

## Watermark maths

At a 40 GiB budget the 88 percent watermark means eviction starts at 35.2
GiB. The 92 percent setting moves that to 36.8 GiB, which buys roughly one
extra render pass of zoom 14 before anything cold is dropped.