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Maurice
3c67afeade
The prefetch dispatched every tile of a trip's bounding box in one
synchronous loop — up to MAX_TILES per trip. A trip spanning a few
countries enumerates thousands of tiles at zoom 10 alone, so logging in
fired ~8k no-cors requests back to back and kept them coming for half a
minute. All of them go through the Workbox fetch handler, which then has
to write a cache entry plus an expiration record per tile, so everything
the app itself requested queued up behind the burst and the UI just sat
there.
Run the queue through a small worker pool instead, and let it stop early
when the user goes offline or logs out.
Two things fall out of that:
- Tiles already in Cache Storage are now skipped before the request is
made, so a resumed or repeated prefetch over a warm cache is nearly
free.
- {s} has to be a pure function of the tile coordinates for that lookup
to hit. The rotating counter gave the same tile a different host on
every run, which also meant caching it up to four times.