feat: add composite sources support WIP

[stepankuzmin]

This PR allows composing multiple table sources into one composite source. Table sources endpoints now support multiple tables in one request. E.g you can request tiles that contain data from multiple tables by listing the tables separated by a comma:

/{schema_name1}.{table_name1},{schema_name2}.{table_name2}.json
/{schema_name1}.{table_name1},{schema_name2}.{table_name2}/0/0/0.pbf

Using with Mapbox GL JS

map.addSource('points', {
  type: 'vector',
  url: `http://0.0.0.0:3000/public.red_points,public.blue_points.json`
});

map.addLayer({
  id: 'red_points',
  type: 'circle',
  source: 'points',
  'source-layer': 'public.red_points',
  paint: {
    'circle-color': 'red'
  }
});

map.addLayer({
  id: 'blue_points',
  type: 'circle',
  source: 'points',
  'source-layer': 'public.blue_points',
  paint: {
    'circle-color': 'blue'
  }
});

You can try this docker image with composite sources support and give any feedback on this

docker pull urbica/martin:pr-107-merge

Relates: #36

[codecov]

Codecov Report

Merging #107 into master will increase coverage by 0.67%.
The diff coverage is 74.00%.

@@            Coverage Diff             @@
##           master     #107      +/-   ##
==========================================
+ Coverage   45.41%   46.08%   +0.67%     
==========================================
  Files          13       14       +1     
  Lines        1319     1341      +22     
==========================================
+ Hits          599      618      +19     
- Misses        720      723       +3     

Impacted Files	Coverage Δ
src/lib.rs	41.11% <ø> (ø)
src/composite_source.rs	66.66% <66.66%> (ø)
src/server.rs	43.55% <78.12%> (+3.26%)	⬆️
src/table_source.rs	74.39% <0.00%> (-7.32%)	⬇️

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[sabman]

@stepankuzmin do we might need to think about performance here? I noticed a performance hit on my local setup, as I increased the tables. I have to dig into the code a bit to see what is going on when registering a composite source. But any pointers from you might be useful.

[robert-claypool]

@stepankuzmin, with table sources, I think all column values are added to the tile. Is there some way to exclude columns or can this new composite source be extended to support function sources too?

[robert-claypool]

I've been running this branch daily for weeks now. No issues.

[nicholas-deepblocks]

Hey @stepankuzmin, many thanks to you and the rest of the team for this great piece of software. Any news on this PR? Sure would be handy to make it official.

[stepankuzmin]

Hi everyone,

Sorry for the delay, I'm refactoring this in my free time. I hope to ship it this month

[sabman]

@stepankuzmin let us know if you need any help. Happy to fix the merge conflicts if you like.

[stepankuzmin]

Hi everyone

I've rewritten composite sources support in #184

docker pull urbica/martin:pr-184

Could you please try this new image? If everything works well for you, I'm going to release it as v0.6.0

/cc @sabman @robert-claypool @nicholas-deepblocks