Raster rendering very slow and stalls above zoom level 15

[nhantt-gis]

Hi team,

I'm currently using TileServer-GL to render raster tiles from a vector .mbtiles source. Everything works fine up to zoom level 15, but I encounter two major issues:

🔴 1. Raster rendering is extremely slow at higher zoom levels
Raster tiles from vector sources take several seconds to render at zoom level 15.

Above zoom 15, requests either hang indefinitely (pending in the browser) or result in no tile being rendered.

CPU usage spikes and tiles are not served in reasonable time, causing major usability issues.

🔴 2. Requests beyond max zoom level get stuck pending
When the .mbtiles source only contains tiles up to zoom level 15, any request at z=16+ will be pending instead of returning a proper 404 or empty tile.

This can cause browsers to hang or repeatedly retry.

🔧 Environment:
OS: Ubuntu 22.04 LTS (Docker environment)
CPU: Intel Core i7-12700 (12 cores: 8P + 4E, 20 threads)
RAM: 32GB DDR4
GPU: NVIDIA GeForce RTX 3050 (8GB VRAM)
Storage: SSD NVMe (500GB)
Node.js Version: v18.x
Docker: v24.x
TileServer-GL Version: latest

[acalcutt]

Do you think you could possibly have a missing font that only shows up at zoom 15? Usually if I see stalling it is because a resource maplibre-native requires does not exist.

[nhantt-gis]

Thank you for your suggestion.

I’ve verified that all required fonts are available and rendering correctly when using the vt-raster-converter library to generate raster tiles from the same vector data and style. However, when using the same resources (data, fonts, and style), tileserver-gl only renders raster tiles up to zoom level 15. This behavior suggests the issue is specific to tileserver-gl, rather than missing resources.

Please let me know if you have any ideas or settings in tileserver-gl that might be limiting the raster tile rendering beyond zoom level 15.