Slow MGLOfflineStorage removePack hang the map

[halset]

Steps to reproduce

1. Load some offline packs with a total of around 500MB tiles.
2. call MGLOfflineStorage removePack to remove a small pack of around 20MB of tiles.
3. Zoom or pan the map to an area where there are no tiles in the cache.

Expected behavior

The map should work right away and the delete complete after some seconds.

Actual behavior

The map will not load new tiles until the pack remove are completed and this takes around 3 minutes on a iPhone X.

Configuration

Mapbox SDK versions: 5.4.0
iOS/macOS versions: 13.1.1
Device/simulator models:
Xcode version: 11.1

Here is a screen shot from Profiler showing this delete going on for several minutes. Mainly working on a db exec in deleteRegion. Perhaps the VACUUM?

[halset]

Reading up on https://www.sqlite.org/lang_vacuum.html , it says that:

The VACUUM command works by copying the contents of the database into a temporary database file and then overwriting the original with the contents of the temporary file.

So, it probably tries to copy the ~480MB database? The change from auto_vacuum to vacuum seem to be from bf0be56 that was a part of #14901, but I do not know if that is relevant.

[julianrex]

Hi @halset - just to confirm - when you say the this "hangs the map" you mean that new tiles aren't displaying, rather than interaction being completely blocked?

cc @tmpsantos for VACUUM discussions

[halset]

@julianrex Zooming and paning are fine and the UI responds, but new tiles are not loaded in to the map. Like if the device lost internet connection. I have not checked if cached tiles are also not loaded.

[halset]

Current workaround for me is to skip vacuum in deleteRegion. The delete is then very fast and map tile loading does not suffer. The downside is that the database then probably just grows.

[halset]

Seems like #15837 is relevant to this.