Building a High-Performance RAG Solution with Pgvectorscale and Python

This tutorial will guide you through setting up and using pgvectorscale with Docker and Python, leveraging OpenAI's powerful text-embedding-3-small model for embeddings. You'll learn to build a cutting-edge RAG (Retrieval-Augmented Generation) solution, combining advanced retrieval techniques (including hybrid search) with intelligent answer generation based on the retrieved context. Perfect for AI engineers looking to enhance their projects with state-of-the-art vector search and generation capabilities with the power of PostgreSQL.

Pgvectorscale Documentation

For more information about using PostgreSQL as a vector database in AI applications with Timescale, check out these resources:

• GitHub Repository: pgvectorscale
• Blog Post: PostgreSQL and Pgvector: Now Faster Than Pinecone, 75% Cheaper, and 100% Open Source
• Blog Post: RAG Is More Than Just Vector Search
• Blog Post: A Python Library for Using PostgreSQL as a Vector Database in AI Applications

Why PostgreSQL?

Using PostgreSQL with pgvectorscale as your vector database offers several key advantages over dedicated vector databases:

• PostgreSQL is a robust, open-source database with a rich ecosystem of tools, drivers, and connectors. This ensures transparency, community support, and continuous improvements.

• By using PostgreSQL, you can manage both your relational and vector data within a single database. This reduces operational complexity, as there's no need to maintain and synchronize multiple databases.

• Pgvectorscale enhances pgvector with faster search capabilities, higher recall, and efficient time-based filtering. It leverages advanced indexing techniques, such as the DiskANN-inspired index, to significantly speed up Approximate Nearest Neighbor (ANN) searches.

Pgvectorscale Vector builds on top of pgvector, offering improved performance and additional features, making PostgreSQL a powerful and versatile choice for AI applications.

Prerequisites

• Docker
• Python 3.7+
• OpenAI API key
• PostgreSQL GUI client

Steps

1. Set up Docker environment
2. Connect to the database using a PostgreSQL GUI client (I use TablePlus)
3. Create a Python script to insert document chunks as vectors using OpenAI embeddings
4. Create a Python function to perform similarity search

Detailed Instructions

1. Set up Docker environment

Create a docker-compose.yml file with the following content:

services:
  timescaledb:
    image: timescale/timescaledb-ha:pg16
    container_name: timescaledb
    environment:
      - POSTGRES_DB=postgres
      - POSTGRES_PASSWORD=password
    ports:
      - "5432:5432"
    volumes:
      - timescaledb_data:/var/lib/postgresql/data
    restart: unless-stopped

volumes:
  timescaledb_data:

Run the Docker container:

docker compose up -d

2. Connect to the database using a PostgreSQL GUI client

• Open client
• Create a new connection with the following details:
  • Host: localhost
  • Port: 5432
  • User: postgres
  • Password: password
  • Database: postgres

3. Create a Python script to insert document chunks as vectors

See insert_vectors.py for the implementation. This script uses OpenAI's text-embedding-3-small model to generate embeddings.

4. Create a Python function to perform similarity search

See similarity_search.py for the implementation. This script also uses OpenAI's text-embedding-3-small model for query embedding.

Usage

1. Create a copy of example.env and rename it to .env
2. Open .env and fill in your OpenAI API key. Leave the database settings as is
3. Run the Docker container
4. Install the required Python packages using pip install -r requirements.txt
5. Execute insert_vectors.py to populate the database
6. Play with similarity_search.py to perform similarity searches

Using ANN search indexes to speed up queries

Timescale Vector offers indexing options to accelerate similarity queries, particularly beneficial for large vector datasets (10k+ vectors):

1. Supported indexes:

   • timescale_vector_index (default): A DiskANN-inspired graph index
   • pgvector's HNSW: Hierarchical Navigable Small World graph index
   • pgvector's IVFFLAT: Inverted file index

2. The DiskANN-inspired index is Timescale's latest offering, providing improved performance. Refer to the Timescale Vector explainer blog for detailed information and benchmarks.

For optimal query performance, creating an index on the embedding column is recommended, especially for large vector datasets.

Cosine Similarity in Vector Search

What is Cosine Similarity?

Cosine similarity measures the cosine of the angle between two vectors in a multi-dimensional space. It's a measure of orientation rather than magnitude.

• Range: -1 to 1 (for normalized vectors, which is typical in text embeddings)
• 1: Vectors point in the same direction (most similar)
• 0: Vectors are orthogonal (unrelated)
• -1: Vectors point in opposite directions (most dissimilar)

Cosine Distance

In pgvector, the <=> operator computes cosine distance, which is 1 - cosine similarity.

• Range: 0 to 2
• 0: Identical vectors (most similar)
• 1: Orthogonal vectors
• 2: Opposite vectors (most dissimilar)

Interpreting Results

When you get results from similarity_search:

• Lower distance values indicate higher similarity.
• A distance of 0 would mean exact match (rarely happens with embeddings).
• Distances closer to 0 indicate high similarity.
• Distances around 1 suggest little to no similarity.
• Distances approaching 2 indicate opposite meanings (rare in practice).