Added IndexLSH to the demo (#4009)

Summary:
Demonstrate IndexLSH does not need training or codebook serialization

Pull Request resolved: #4009

Reviewed By: junjieqi

Differential Revision: D65274645

Pulled By: asadoughi

fbshipit-source-id: c9af463757edbd07cc07b1cf607b88373fa334c4

demos/index_pq_flat_separate_codes_from_codebook.py

@@ -1,20 +1,19 @@
-#!/usr/bin/env -S grimaldi --kernel faiss_binary_local
+#!/usr/bin/env -S grimaldi --kernel bento_kernel_faiss
 # Copyright (c) Meta Platforms, Inc. and affiliates.
 #
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
-
 # fmt: off
 # flake8: noqa
 
 
 """:md
-# IndexPQ: separate codes from codebook
+# Serializing codes separately, with IndexLSH and IndexPQ
+
+Let's say, for example, you have a few vector embeddings per user
+and want to shard a flat index by user so you can re-use the same LSH or PQ method
+ for all users but store each user's codes independently.
 
-This notebook demonstrates how to separate serializing and deserializing the PQ codebook
- (via faiss.write_index for IndexPQ) independently of the vector codes. For example, in the case
- where you have a few vector embeddings per user and want to shard the flat index by user you 
- can re-use the same PQ method for all users but store each user's codes independently. 
 
 """
 
@@ -24,11 +23,9 @@
 
 """:py"""
 d = 768
-n = 10000
+n = 1_000
 ids = np.arange(n).astype('int64')
 training_data = np.random.rand(n, d).astype('float32')
-M = d//8
-nbits = 8
 
 """:py"""
 def read_ids_codes():
@@ -50,9 +47,76 @@ def write_template_index(template_index):
 def read_template_index_instance():
     return faiss.read_index("/tmp/template.index")
 
+""":md
+## IndexLSH: separate codes
+
+The first half of this notebook demonstrates how to store LSH codes. Unlike PQ, LSH does not require training. In fact, it's compression method, a random projections matrix, is deterministic on construction based on a random seed value that's [hardcoded](https://github.com/facebookresearch/faiss/blob/2c961cc308ade8a85b3aa10a550728ce3387f625/faiss/IndexLSH.cpp#L35).
+"""
+
 """:py"""
-# at train time
+nbits = 1536
+
+""":py"""
+# demonstrating encoding is deterministic
+
+codes = []
+database_vector_float32 = np.random.rand(1, d).astype(np.float32)
+for i in range(10):
+    index = faiss.IndexIDMap2(faiss.IndexLSH(d, nbits))
+    code = index.index.sa_encode(database_vector_float32)
+    codes.append(code)
+
+for i in range(1, 10):
+    assert np.array_equal(codes[0], codes[i])
+
+""":py"""
+# new database vector
+
+ids, codes = read_ids_codes()
+database_vector_id, database_vector_float32 = max(ids) + 1 if ids is not None else 1, np.random.rand(1, d).astype(np.float32)
+index = faiss.IndexIDMap2(faiss.IndexLSH(d, nbits))
+
+code = index.index.sa_encode(database_vector_float32)
 
+if ids is not None and codes is not None:
+    ids = np.concatenate((ids, [database_vector_id]))
+    codes = np.vstack((codes, code))
+else:
+    ids = np.array([database_vector_id])
+    codes = np.array([code])
+
+write_ids_codes(ids, codes)
+
+""":py '2840581589434841'"""
+# then at query time
+
+query_vector_float32 = np.random.rand(1, d).astype(np.float32)
+index = faiss.IndexIDMap2(faiss.IndexLSH(d, nbits))
+ids, codes = read_ids_codes()
+
+index.add_sa_codes(codes, ids)
+
+index.search(query_vector_float32, k=5)
+
+""":py"""
+!rm /tmp/ids.npy /tmp/codes.npy
+
+""":md
+## IndexPQ: separate codes from codebook
+
+The second half of this notebook demonstrates how to separate serializing and deserializing the PQ codebook
+ (via faiss.write_index for IndexPQ) independently of the vector codes. For example, in the case
+ where you have a few vector embeddings per user and want to shard the flat index by user you 
+ can re-use the same PQ method for all users but store each user's codes independently. 
+
+"""
+
+""":py"""
+M = d//8
+nbits = 8
+
+""":py"""
+# at train time
 template_index = faiss.index_factory(d, f"IDMap2,PQ{M}x{nbits}")
 template_index.train(training_data)
 write_template_index(template_index)
@@ -61,8 +125,8 @@ def read_template_index_instance():
 # New database vector
 
 index = read_template_index_instance()
-database_vector_id, database_vector_float32 = np.random.randint(10000), np.random.rand(1, d).astype(np.float32)
 ids, codes = read_ids_codes()
+database_vector_id, database_vector_float32 = max(ids) + 1 if ids is not None else 1, np.random.rand(1, d).astype(np.float32)
 
 code = index.index.sa_encode(database_vector_float32)
 
@@ -75,7 +139,7 @@ def read_template_index_instance():
 
 write_ids_codes(ids, codes)
 
-""":py '331546060044009'"""
+""":py '1858280061369209'"""
 # then at query time
 query_vector_float32 = np.random.rand(1, d).astype(np.float32)
 id_wrapper_index = read_template_index_instance()
@@ -87,3 +151,153 @@ def read_template_index_instance():
 
 """:py"""
 !rm /tmp/ids.npy /tmp/codes.npy /tmp/template.index
+
+""":md
+## Comparing these methods
+
+- methods: Flat, LSH, PQ
+- vary cost: nbits, M for 1x, 2x, 4x, 8x, 16x, 32x compression
+- measure: recall@1
+
+We don't measure latency as the number of vectors per user shard is insignificant.
+
+"""
+
+""":py '2898032417027201'"""
+n, d
+
+""":py"""
+database_vector_ids, database_vector_float32s = np.arange(n), np.random.rand(n, d).astype(np.float32)
+query_vector_float32s = np.random.rand(n, d).astype(np.float32)
+
+""":py"""
+index = faiss.index_factory(d, "IDMap2,Flat")
+index.add_with_ids(database_vector_float32s, database_vector_ids)
+_, ground_truth_result_ids= index.search(query_vector_float32s, k=1)
+
+""":py '857475336204238'"""
+from dataclasses import dataclass
+
+pq_m_nbits = (
+    # 96 bytes
+    (96, 8),
+    (192, 4),
+    # 192 bytes
+    (192, 8),
+    (384, 4),
+    # 384 bytes
+    (384, 8),
+    (768, 4),
+)
+lsh_nbits = (768, 1536, 3072, 6144, 12288, 24576)
+
+
+@dataclass
+class Record:
+    type_: str
+    index: faiss.Index
+    args: tuple
+    recall: float
+
+
+results = []
+
+for m, nbits in pq_m_nbits:
+    print("pq", m, nbits)
+    index = faiss.index_factory(d, f"IDMap2,PQ{m}x{nbits}")
+    index.train(training_data)
+    index.add_with_ids(database_vector_float32s, database_vector_ids)
+    _, result_ids = index.search(query_vector_float32s, k=1)
+    recall = sum(result_ids == ground_truth_result_ids)
+    results.append(Record("pq", index, (m, nbits), recall))
+
+for nbits in lsh_nbits:
+    print("lsh", nbits)
+    index = faiss.IndexIDMap2(faiss.IndexLSH(d, nbits))
+    index.add_with_ids(database_vector_float32s, database_vector_ids)
+    _, result_ids = index.search(query_vector_float32s, k=1)
+    recall = sum(result_ids == ground_truth_result_ids)
+    results.append(Record("lsh", index, (nbits,), recall))
+
+""":py '556918346720794'"""
+import matplotlib.pyplot as plt
+import numpy as np
+
+def create_grouped_bar_chart(x_values, y_values_list, labels_list, xlabel, ylabel, title):
+    num_bars_per_group = len(x_values)
+
+    plt.figure(figsize=(12, 6))
+
+    for x, y_values, labels in zip(x_values, y_values_list, labels_list):
+        num_bars = len(y_values)
+        bar_width = 0.08 * x
+        bar_positions = np.arange(num_bars) * bar_width - (num_bars - 1) * bar_width / 2 + x
+
+        bars = plt.bar(bar_positions, y_values, width=bar_width)
+
+        for bar, label in zip(bars, labels):
+            height = bar.get_height()
+            plt.annotate(
+                label,
+                xy=(bar.get_x() + bar.get_width() / 2, height),
+                xytext=(0, 3),
+                textcoords="offset points",
+                ha='center', va='bottom'
+            )
+
+    plt.xscale('log')
+    plt.xlabel(xlabel)
+    plt.ylabel(ylabel)
+    plt.title(title)
+    plt.xticks(x_values, labels=[str(x) for x in x_values])
+    plt.tight_layout()
+    plt.show()
+
+# # Example usage:
+# x_values = [1, 2, 4, 8, 16, 32]
+# y_values_list = [
+#     [2.5, 3.6, 1.8],
+#     [3.0, 2.8],
+#     [2.5, 3.5, 4.0, 1.0],
+#     [4.2],
+#     [3.0, 5.5, 2.2],
+#     [6.0, 4.5]
+# ]
+# labels_list = [
+#     ['A1', 'B1', 'C1'],
+#     ['A2', 'B2'],
+#     ['A3', 'B3', 'C3', 'D3'],
+#     ['A4'],
+#     ['A5', 'B5', 'C5'],
+#     ['A6', 'B6']
+# ]
+
+# create_grouped_bar_chart(x_values, y_values_list, labels_list, "x axis", "y axis", "title")
+
+""":py '1630106834206134'"""
+# x-axis: compression ratio
+# y-axis: recall@1
+
+from collections import defaultdict
+
+x = defaultdict(list)
+x[1].append(("flat", 1.00))
+for r in results:
+    y_value = r.recall[0] / n
+    x_value = int(d * 4 / r.index.sa_code_size())
+    label = None
+    if r.type_ == "pq":
+        label = f"PQ{r.args[0]}x{r.args[1]}"
+    if r.type_ == "lsh":
+        label = f"LSH{r.args[0]}"
+    x[x_value].append((label, y_value))
+
+x_values = sorted(list(x.keys()))
+create_grouped_bar_chart(
+    x_values,
+    [[e[1] for e in x[x_value]] for x_value in x_values],
+    [[e[0] for e in x[x_value]] for x_value in x_values],
+    "compression ratio",
+    "recall@1  q=1,000 queries",
+    "recall@1 for a database of n=1,000 d=768 vectors",
+)