How does vector search scale with data size?

Vector search scalability depends on two main factors: the indexing method used and the computational resources available. As data size grows, the challenge lies in maintaining both speed and accuracy while searching through high-dimensional vectors. Traditional exact search methods, like linear scans (comparing a query vector to every vector in the dataset), become impractical for large datasets because their time complexity scales linearly with data size. For example, searching through 1 million vectors might take milliseconds, but 1 billion vectors could take minutes or hours, making real-time queries impossible. To address this, approximate nearest neighbor (ANN) algorithms are used, which trade some accuracy for significantly faster query times.

ANN algorithms like HNSW (Hierarchical Navigable Small World), ANNOY (Approximate Nearest Neighbors Oh Yeah), or FAISS (Facebook AI Similarity Search) optimize search efficiency by organizing vectors into specialized data structures. For instance, HNSW builds a layered graph where each layer allows faster navigation to nearby vectors, reducing the number of comparisons needed. FAISS uses techniques like vector quantization, where vectors are grouped into clusters, and searches focus on the most relevant clusters. These methods allow query times to scale sublinearly with data size. For example, a dataset of 100 million vectors might be searchable in 10 milliseconds using HNSW, whereas a linear scan would take orders of magnitude longer. However, larger datasets still require more memory and computational power, which leads to trade-offs in hardware costs and infrastructure complexity.

Practical scaling also involves distributed systems and partitioning strategies. For very large datasets (e.g., billions of vectors), the index is often split across multiple machines using sharding. Each shard handles a subset of the data, and queries are parallelized across shards. Tools like Elasticsearch’s vector search or distributed versions of FAISS support this approach. Additionally, preprocessing steps like dimensionality reduction (e.g., using PCA or autoencoders) can reduce vector size, improving both storage and search efficiency. However, developers must balance these optimizations: aggressive dimensionality reduction might degrade search quality, while over-partitioning can increase network overhead. For example, a system handling 10 billion vectors might use 64-dimensional vectors (reduced from 512 dimensions) and 100 shards, achieving latency under 50 milliseconds per query. The key is aligning the algorithm, infrastructure, and data characteristics to meet specific performance and accuracy requirements.