Optimize vector index performance for latency, recall, and memory. Use when tuning HNSW parameters, selecting quantization strategies, or scaling vector search infrastructure.
Guide to optimizing vector indexes for production performance.
Data Size Recommended Index
────────────────────────────────────────
< 10K vectors → Flat (exact search)
10K - 1M → HNSW
1M - 100M → HNSW + Quantization
> 100M → IVF + PQ or DiskANN
| Parameter | Default | Effect |
|---|---|---|
| M | 16 | Connections per node, ↑ = better recall, more memory |
| efConstruction | 100 | Build quality, ↑ = better index, slower build |
| efSearch | 50 | Search quality, ↑ = better recall, slower search |
Full Precision (FP32): 4 bytes × dimensions
Half Precision (FP16): 2 bytes × dimensions
INT8 Scalar: 1 byte × dimensions
Product Quantization: ~32-64 bytes total
Binary: dimensions/8 bytes
import numpy as np
from typing import List, Tuple
import time
def benchmark_hnsw_parameters(
vectors: np.ndarray,
queries: np.ndarray,
ground_truth: np.ndarray,
m_values: List[int] = [8, 16, 32, 64],
ef_construction_values: List[int] = [64, 128, 256],
ef_search_values: List[int] = [32, 64, 128, 256]
) -> List[dict]:
"""Benchmark different HNSW configurations."""
import hnswlib
results = []
dim = vectors.shape[1]
n = vectors.shape[0]
for m in m_values:
for ef_construction in ef_construction_values:
# Build index
index = hnswlib.Index(space='cosine', dim=dim)
index.init_index(max_elements=n, M=m, ef_construction=ef_construction)
build_start = time.time()
index.add_items(vectors)
build_time = time.time() - build_start
# Get memory usage
memory_bytes = index.element_count * (
dim * 4 + # Vector storage
m * 2 * 4 # Graph edges (approximate)
)
for ef_search in ef_search_values:
index.set_ef(ef_search)
# Measure search
search_start = time.time()
labels, distances = index.knn_query(queries, k=10)
search_time = time.time() - search_start
# Calculate recall
recall = calculate_recall(labels, ground_truth, k=10)
results.append({
"M": m,
"ef_construction": ef_construction,
"ef_search": ef_search,
"build_time_s": build_time,
"search_time_ms": search_time * 1000 / len(queries),
"recall@10": recall,
"memory_mb": memory_bytes / 1024 / 1024
})
return results
def calculate_recall(predictions: np.ndarray, ground_truth: np.ndarray, k: int) -> float:
"""Calculate recall@k."""
correct = 0
for pred, truth in zip(predictions, ground_truth):
correct += len(set(pred[:k]) & set(truth[:k]))
return correct / (len(predictions) * k)
def recommend_hnsw_params(
num_vectors: int,
target_recall: float = 0.95,
max_latency_ms: float = 10,
available_memory_gb: float = 8
) -> dict:
"""Recommend HNSW parameters based on requirements."""
# Base recommendations
if num_vectors < 100_000:
m = 16
ef_construction = 100
elif num_vectors < 1_000_000:
m = 32
ef_construction = 200
else:
m = 48
ef_construction = 256
# Adjust ef_search based on recall target
if target_recall >= 0.99:
ef_search = 256
elif target_recall >= 0.95:
ef_search = 128
else:
ef_search = 64
return {
"M": m,
"ef_construction": ef_construction,
"ef_search": ef_search,
"notes": f"Estimated for {num_vectors:,} vectors, {target_recall:.0%} recall"
}
import numpy as np
from typing import Optional
class VectorQuantizer:
"""Quantization strategies for vector compression."""
@staticmethod
def scalar_quantize_int8(
vectors: np.ndarray,
min_val: Optional[float] = None,
max_val: Optional[float] = None
) -> Tuple[np.ndarray, dict]:
"""Scalar quantization to INT8."""
if min_val is None:
min_val = vectors.min()
if max_val is None:
max_val = vectors.max()
# Scale to 0-255 range
scale = 255.0 / (max_val - min_val)
quantized = np.clip(
np.round((vectors - min_val) * scale),
0, 255
).astype(np.uint8)
params = {"min_val": min_val, "max_val": max_val, "scale": scale}
return quantized, params
@staticmethod
def dequantize_int8(
quantized: np.ndarray,
params: dict
) -> np.ndarray:
"""Dequantize INT8 vectors."""
return quantized.astype(np.float32) / params["scale"] + params["min_val"]
@staticmethod
def product_quantize(
vectors: np.ndarray,
n_subvectors: int = 8,
n_centroids: int = 256
) -> Tuple[np.ndarray, dict]:
"""Product quantization for aggressive compression."""
from sklearn.cluster import KMeans
n, dim = vectors.shape
assert dim % n_subvectors == 0
subvector_dim = dim // n_subvectors
codebooks = []
codes = np.zeros((n, n_subvectors), dtype=np.uint8)
for i in range(n_subvectors):
start = i * subvector_dim
end = (i + 1) * subvector_dim
subvectors = vectors[:, start:end]
kmeans = KMeans(n_clusters=n_centroids, random_state=42)
codes[:, i] = kmeans.fit_predict(subvectors)
codebooks.append(kmeans.cluster_centers_)
params = {
"codebooks": codebooks,
"n_subvectors": n_subvectors,
"subvector_dim": subvector_dim
}
return codes, params
@staticmethod
def binary_quantize(vectors: np.ndarray) -> np.ndarray:
"""Binary quantization (sign of each dimension)."""
# Convert to binary: positive = 1, negative = 0
binary = (vectors > 0).astype(np.uint8)
# Pack bits into bytes
n, dim = vectors.shape
packed_dim = (dim + 7) // 8
packed = np.zeros((n, packed_dim), dtype=np.uint8)
for i in range(dim):
byte_idx = i // 8
bit_idx = i % 8
packed[:, byte_idx] |= (binary[:, i] << bit_idx)
return packed
def estimate_memory_usage(
num_vectors: int,
dimensions: int,
quantization: str = "fp32",
index_type: str = "hnsw",
hnsw_m: int = 16
) -> dict:
"""Estimate memory usage for different configurations."""
# Vector storage
bytes_per_dimension = {
"fp32": 4,
"fp16": 2,
"int8": 1,
"pq": 0.05, # Approximate
"binary": 0.125
}
vector_bytes = num_vectors * dimensions * bytes_per_dimension[quantization]
# Index overhead
if index_type == "hnsw":
# Each node has ~M*2 edges, each edge is 4 bytes (int32)
index_bytes = num_vectors * hnsw_m * 2 * 4
elif index_type == "ivf":
# Inverted lists + centroids
index_bytes = num_vectors * 8 + 65536 * dimensions * 4
else:
index_bytes = 0
total_bytes = vector_bytes + index_bytes
return {
"vector_storage_mb": vector_bytes / 1024 / 1024,
"index_overhead_mb": index_bytes / 1024 / 1024,
"total_mb": total_bytes / 1024 / 1024,
"total_gb": total_bytes / 1024 / 1024 / 1024
}
from qdrant_client import QdrantClient
from qdrant_client.http import models
def create_optimized_collection(
client: QdrantClient,
collection_name: str,
vector_size: int,
num_vectors: int,
optimize_for: str = "balanced" # "recall", "speed", "memory"
) -> None:
"""Create collection with optimized settings."""
# HNSW configuration based on optimization target
hnsw_configs = {
"recall": models.HnswConfigDiff(m=32, ef_construct=256),
"speed": models.HnswConfigDiff(m=16, ef_construct=64),
"balanced": models.HnswConfigDiff(m=16, ef_construct=128),
"memory": models.HnswConfigDiff(m=8, ef_construct=64)
}
# Quantization configuration
quantization_configs = {
"recall": None, # No quantization for max recall
"speed": models.ScalarQuantization(
scalar=models.ScalarQuantizationConfig(
type=models.ScalarType.INT8,
quantile=0.99,
always_ram=True
)
),
"balanced": models.ScalarQuantization(
scalar=models.ScalarQuantizationConfig(
type=models.ScalarType.INT8,
quantile=0.99,
always_ram=False
)
),
"memory": models.ProductQuantization(
product=models.ProductQuantizationConfig(
compression=models.CompressionRatio.X16,
always_ram=False
)
)
}
# Optimizer configuration
optimizer_configs = {
"recall": models.OptimizersConfigDiff(
indexing_threshold=10000,
memmap_threshold=50000
),
"speed": models.OptimizersConfigDiff(
indexing_threshold=5000,
memmap_threshold=20000
),
"balanced": models.OptimizersConfigDiff(
indexing_threshold=20000,
memmap_threshold=50000
),
"memory": models.OptimizersConfigDiff(
indexing_threshold=50000,
memmap_threshold=10000 # Use disk sooner
)
}
client.create_collection(
collection_name=collection_name,
vectors_config=models.VectorParams(
size=vector_size,
distance=models.Distance.COSINE
),
hnsw_config=hnsw_configs[optimize_for],
quantization_config=quantization_configs[optimize_for],
optimizers_config=optimizer_configs[optimize_for]
)
def tune_search_parameters(
client: QdrantClient,
collection_name: str,
target_recall: float = 0.95
) -> dict:
"""Tune search parameters for target recall."""
# Search parameter recommendations
if target_recall >= 0.99:
search_params = models.SearchParams(
hnsw_ef=256,
exact=False,
quantization=models.QuantizationSearchParams(
ignore=True, # Don't use quantization for search
rescore=True
)
)
elif target_recall >= 0.95:
search_params = models.SearchParams(
hnsw_ef=128,
exact=False,
quantization=models.QuantizationSearchParams(
ignore=False,
rescore=True,
oversampling=2.0
)
)
else:
search_params = models.SearchParams(
hnsw_ef=64,
exact=False,
quantization=models.QuantizationSearchParams(
ignore=False,
rescore=False
)
)
return search_params
import time
from dataclasses import dataclass
from typing import List
import numpy as np
@dataclass
class SearchMetrics:
latency_p50_ms: float
latency_p95_ms: float
latency_p99_ms: float
recall: float
qps: float
class VectorSearchMonitor:
"""Monitor vector search performance."""
def __init__(self, ground_truth_fn=None):
self.latencies = []
self.recalls = []
self.ground_truth_fn = ground_truth_fn
def measure_search(
self,
search_fn,
query_vectors: np.ndarray,
k: int = 10,
num_iterations: int = 100
) -> SearchMetrics:
"""Benchmark search performance."""
latencies = []
for _ in range(num_iterations):
for query in query_vectors:
start = time.perf_counter()
results = search_fn(query, k=k)
latency = (time.perf_counter() - start) * 1000
latencies.append(latency)
latencies = np.array(latencies)
total_queries = num_iterations * len(query_vectors)
total_time = sum(latencies) / 1000 # seconds
return SearchMetrics(
latency_p50_ms=np.percentile(latencies, 50),
latency_p95_ms=np.percentile(latencies, 95),
latency_p99_ms=np.percentile(latencies, 99),
recall=self._calculate_recall(search_fn, query_vectors, k) if self.ground_truth_fn else 0,
qps=total_queries / total_time
)
def _calculate_recall(self, search_fn, queries: np.ndarray, k: int) -> float:
"""Calculate recall against ground truth."""
if not self.ground_truth_fn:
return 0
correct = 0
total = 0
for query in queries:
predicted = set(search_fn(query, k=k))
actual = set(self.ground_truth_fn(query, k=k))
correct += len(predicted & actual)
total += k
return correct / total
def profile_index_build(
build_fn,
vectors: np.ndarray,
batch_sizes: List[int] = [1000, 10000, 50000]
) -> dict:
"""Profile index build performance."""
results = {}
for batch_size in batch_sizes:
times = []
for i in range(0, len(vectors), batch_size):
batch = vectors[i:i + batch_size]
start = time.perf_counter()
build_fn(batch)
times.append(time.perf_counter() - start)
results[batch_size] = {
"avg_batch_time_s": np.mean(times),
"vectors_per_second": batch_size / np.mean(times)
}
return results
