Reconfigurable Inverted Index (Rii): IVFPQ-based fast and memory efficient approximate nearest neighbor search method
with a subset-search functionality.

Reference:

• Y. Matsui, R. Hinami, and S. Satoh, “Reconfigurable Inverted Index“, ACM Multimedia 2018 (oral). [paper] [project]

Summary of features

The search can be operated for a subset of a database.	Rii remains fast even after many new items are added.

• Fast and memory efficient ANN. Rii enables you to run billion-scale search in less than 10 ms.
• You can run the search over a subset of the whole database
• Rii Remains fast even after many vectors are newly added (i.e., the data structure can be reconfigured)

Installing

You can install the package via pip. This library works with Python 3.6+ on linux/mac/wsl/Windows10

pip install rii

Documentation

• Tutorial
• Tips
• API

Usage

Basic ANN

import rii
import nanopq
import numpy as np
N, Nt, D = 10000, 1000, 128
X = np.random.random((N, D)).astype(np.float32)  # 10,000 128-dim vectors to be searched
Xt = np.random.random((Nt, D)).astype(np.float32)  # 1,000 128-dim vectors for training
q = np.random.random((D,)).astype(np.float32)  # a 128-dim vector
# Prepare a PQ/OPQ codec with M=32 sub spaces
codec = nanopq.PQ(M=32).fit(vecs=Xt)  # Trained using Xt
# Instantiate a Rii class with the codec
e = rii.Rii(fine_quantizer=codec)
# Add vectors
e.add_configure(vecs=X)
# Search
ids, dists = e.query(q=q, topk=3)
print(ids, dists)  # e.g., [7484 8173 1556] [15.06257439 15.38533878 16.16935158]

Note that you can construct a PQ codec and instantiate the Rii class at the same time if you want.

e = rii.Rii(fine_quantizer=nanopq.PQ(M=32).fit(vecs=Xt))
e.add_configure(vecs=X)

Furthermore, you can even write them in one line by chaining a function.

e = rii.Rii(fine_quantizer=nanopq.PQ(M=32).fit(vecs=Xt)).add_configure(vecs=X)

Subset search

# The search can be conducted over a subset of the database
target_ids = np.array([85, 132, 236, 551, 694, 728, 992, 1234]) # Specified by IDs
# For windows, you must specify dtype=np.int64 as follows.
# target_ids = np.array([85, 132, 236, 551, 694, 728, 992, 1234], dtype=np.int64)  
ids, dists = e.query(q=q, topk=3, target_ids=target_ids)
print(ids, dists)  # e.g., [728  85 132] [14.80522156 15.92787838 16.28690338]

Data addition and reconfiguration

# Add new vectors
X2 = np.random.random((1000, D)).astype(np.float32)
e.add(vecs=X2)  # Now N is 11000
e.query(q=q)  # Ok. (0.12 msec / query)
# However, if you add quite a lot of vectors, the search might become slower
# because the data structure has been optimized for the initial item size (N=10000)
X3 = np.random.random((1000000, D)).astype(np.float32) 
e.add(vecs=X3)  # A lot. Now N is 1011000
e.query(q=q)  # Slower (0.96 msec/query)
# In such case, run the reconfigure function. That updates the data structure
e.reconfigure()
e.query(q=q)  # Ok. (0.21 msec / query)

I/O by pickling

import pickle
with open('rii.pkl', 'wb') as f:
    pickle.dump(e, f)
with open('rii.pkl', 'rb') as f:
    e_dumped = pickle.load(f)  # e_dumped is identical to e

Util functions

# Print the current parameters
e.print_params()
# Delete all PQ-codes and posting lists. fine_quantizer is kept.
e.clear()
# You can switch the verbose flag
e.verbose = False
# You can merge two Rii instances if they have the same fine_quantizer
e1 = rii.Rii(fine_quantizer=codec)
e2 = rii.Rii(fine_quantizer=codec)
e1.add_configure(vecs=X1)
e2.add_configure(vecs=X2)
e1.merge(e2)  # Now e1 contains both X1 and X2

Examples

• Simple tag search
• Benchmark

Author

• Yusuke Matsui

Credits

• The logo is designed by @richardbmx (#4)
• The windows implementation is by @ashleyabraham (#42)
• Fixing the build (#50) and supporting for ARM CPUs (#58) by @timzag