Summary:
This diff streamlines the code that collects results for brute force distance computations for the L2 / IP and range search / knn search combinations.
It introduces a `ResultHandler` template class that abstracts what happens with the computed distances and ids. In addition to the heap result handler and the range search result handler, it introduces a reservoir result handler that improves the search speed for large k (>=100).
Benchmark results (https://fb.quip.com/y0g1ACLEqJXx#OCaACA2Gm45) show that on small datasets (10k) search is 10-50% faster (improvements are larger for small k). There is room for improvement in the reservoir implementation, whose implementation is quite naive currently, but the diff is already useful in its current form.
Experiments on precomputed db vector norms for L2 distance computations were not very concluding performance-wise, so the implementation is removed from IndexFlatL2.
This diff also removes IndexL2BaseShift, which was never used.
Pull Request resolved: https://github.com/facebookresearch/faiss/pull/1502
Test Plan:
```
buck test //faiss/tests/:test_product_quantizer
buck test //faiss/tests/:test_index -- TestIndexFlat
```
Reviewed By: wickedfoo
Differential Revision: D24705464
Pulled By: mdouze
fbshipit-source-id: 270e10b19f3c89ed7b607ec30549aca0ac5027fe
* [c_api] Update impl and interface for v1.5
- move IndexShards to dedicated module IndexShards_c.{h|cpp}
- remove getter/setters to unreachable fields
- reimplement faiss_IndexIVF_imbalance_factor (to use invlists)
- minor IndexIVF documentation tweaks
- Remove QueryResult, provide RangeQueryResult
* [c_api] Document FaissErrorCode
* [c_api] Update GPU impl and interface for v1.5
- Remove unavailable method setTempMemoryFraction
* [c_api] Relicense to MIT
In accordance to the rest of the project
* [c_api] leverage index downcast
- make index downcast declaration+definition possible with macros
- use macros on existing index types
* [c_api] Add IndexLSH to C API
* [c_api] Add Index IO interface
- new header index_io_c.h for access to the index_io.h API
- function`faiss_write_index` and overloads for dumping index to a file
- function`faiss_read_index` and overloads for reading index from a file
- function`faiss_clone_index` for cloning an index
- update C example to save index to a file
* [c_api] Add IndexIDMap and IndexShards API
Lucas Hosseini
Matthijs Douze
Eduardo Pinho