Very slow startup when using large tilesets about mbtileserver HOT 2 CLOSED

Looks like this query takes a long time when the tileset is large:
https://github.com/consbio/mbtileserver/blob/master/mbtiles/mbtiles.go#L134

from mbtileserver.

The issue with this specific mbtiles file is that it has a view for grids but doesn't actually have any grid data. It has many tiles, but all of them have a NULL value for grid_id, so the underlying join used to query out a single grid requires searching through all entries in map (the lookup of tile x, y, z to tile_id and grid_id) trying to join on grid_id.

Since our queries are based on views, so that we don't have to know the underlying table structure, it makes it a little more complex. In this case, we have a valid, but empty grids view. We need to determine what tables are being used to compose that view, and query the underlying table that would contain the grid data.

from mbtileserver.