feat: ScaNN index about pgvecto.rs

[karajan1001]

I'll take this.

[VoVAllen]

@karajan1001 ScaNN might be hard to implement since original code highly coupled with tensorflow. I would suggest DiskANN, since it's designed for disk workload, which is suitable for postgres. And it's also adapted by Milvus.

[karajan1001]

@karajan1001 ScaNN might be hard to implement since original code highly coupled with tensorflow. I would suggest DiskANN, since it's designed for disk workload, which is suitable for postgres. And it's also adapted by Milvus.

Yes, I had looked into their paper and source code and noticed that it's highly coupled with TensorFlow. So it's hard to say how much performance is gotten from the algorithm and how much is gotten from the TensorFlow optimization. I was just about to ask if implementing a ScaNN without the TensorFlow optimization would be a good choice.

[gaocegege]

https://services.google.com/fh/files/misc/scann_for_alloydb_whitepaper.pdf

Here is a whitepaper for SCANN in AlloyDB.