I also developed a service based on the Goldberg paper in the mid 2010s. We flattened and discretized the signature to make it searchable which gave us pretty good results: https://github.com/ProvenanceLabs/image-match
Sorry I haven’t maintained the project in years so it’s unlikely to work out of the box. But who knows, maybe you’ll find something useful here for your project!
The insertion rates were based on the elasticsearch backend, with multiple shards/nodes (using the already flattened image signatures). Don't remember specifics unfortunately. I never tried it with more than 5 lightness buckets, sorry!
Sorry I haven’t maintained the project in years so it’s unlikely to work out of the box. But who knows, maybe you’ll find something useful here for your project!