openstreetmap / openstreetmap/mod_tile
Expire using metatiles zoom levels?
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- Dominant language
- C++
- Stars
- 318
- Forks
- 199
- PR merge metrics
- No merged PRs in 30d
Description
When a tile is expired on, say, zoom level 19, it is marked in the expire list in that zoom level 19. But really we are using metatiles, so always the whole metatile is getting expired. If there are a lot of tiles in the same metatile, they are all in the expire list. In the worst case there are 8x8=64 times the number of entries in the expire list than we would really need. We could just write out expire list on zoom level 16 instead.
So I propose some kind of option to render_expires (and maybe render_list) that says: interpret zoom levels as meta tile zoom levels, not tile zoom levels.
See also: https://github.com/osm2pgsql-dev/osm2pgsql/issues/2190
Contributor guide
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by tracing the render_expires and render_list entry points to see how zoom levels are interpreted and how expire-list entries are generated for metatiles. Compare that behavior with the proposed metatile zoom interpretation and the related issue 2190; done means the option's semantics and affected commands are defined without expanding expiration unnecessarily.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- cpp
- Domain
- backend, performance
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 30/100