List of improvements on the nested field post v0.27.0 RC0

[irevoire]

• Remove a now useless callback in the transform:
  Originally posted by @Kerollmops in Nested fields #458 (comment)
• Use the smartstring crate to store the primary key in the transform. => It should improve the performance but more importantly: it'll reduce memory consumption. Use smartstring to store the external id in our hashmap #493
• See if we can improve the error message for the indexing of geopoints => we were able to show the complete object before. Now that's impossible but we could specify what we didn't find (latitude or longitude) => Improve geosearch error messages and accept string as coord #523
• Skip all the flattening if the object do not need it => rewrite a specialized version of oxidized-json-checker that measure the « depth » in the value (actually it's not the depth because we can have 0 object and 1 array). Maybe we could even create something even easier and faster. Only flatten the required objects #494
• Flatten by fields instead of by document => Stop flattening every field #514
• Maybe we could flatten (and thus index) only the fields that are actually in use (ie in any settings)
• Maybe we could fasten the search by creating a « true » db for the attribute to [ retrieve / highlight / crop ] with all the flattened field in it at the indexing time. Not sure about this one.
• Try to make the flatten-serde-json crate works with obkv directly
• See if there is something to do with bumpalo to make all the small allocations a lot faster when we flatten document and reuse the same buffer between each loops (basically what we're doing with the obkv currently)

[curquiza]

Also, we could add some benchmarks to bench a dataset with nested fields 😇
See: #500

[Kerollmops]

I was trying to take this small one Remove a now useless callback in the transform, but it looks like you use it now, am I right?

[irevoire]

Yes but now it doesn't really represent what it was 😬
#458 (comment)

[irevoire]

Everything has been tested