pgvector Embeddings

Generate vector embeddings using Ollama and store them in PostgreSQL with pgvector. This skill covers the ingestion phase of RAG pipelines.

When to Apply

Use this skill when:

• Generating embeddings for documents or text
• Storing embeddings in PostgreSQL
• Building the ingestion pipeline for RAG
• Converting text to vectors for semantic search
• Chunking documents for better retrieval

Embedding Models

Recommended: nomic-embed-text

The nomic-embed-text model provides 768-dimensional embeddings with good quality and performance:

# Pull the model
ollama pull nomic-embed-text

Model	Dimensions	Speed	Quality
nomic-embed-text	768	Fast	Good
mxbai-embed-large	1024	Medium	Better
all-minilm	384	Very Fast	Acceptable

OllamaClient Implementation

Create a TypeScript client for generating embeddings:

// src/utils/ollama.ts
import fetch from 'cross-fetch';

interface OllamaEmbeddingResponse {
  embedding: number[];
}

export class OllamaClient {
  private baseUrl: string;

  constructor(baseUrl?: string) {
    this.baseUrl = baseUrl || process.env.OLLAMA_HOST || 'http://localhost:11434';
  }

  async generateEmbedding(text: string, model: string = 'nomic-embed-text'): Promise<number[]> {
    const response = await fetch(`${this.baseUrl}/api/embeddings`, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        model,
        prompt: text,
      }),
    });

    if (!response.ok) {
      throw new Error(`Failed to generate embedding: ${response.statusText}`);
    }

    const data: OllamaEmbeddingResponse = await response.json();
    return data.embedding;
  }
}

Storing Embeddings

Format Vector for PostgreSQL

pgvector expects vectors in bracket notation:

const formatVector = (embedding: number[]): string => `[${embedding.join(',')}]`;

Insert Document with Embedding

import { Pool } from 'pg';
import { OllamaClient } from './utils/ollama';

const pool = new Pool();
const ollama = new OllamaClient();

async function addDocument(title: string, content: string, metadata: Record<string, unknown> = {}) {
  // Generate embedding for the full document
  const embedding = await ollama.generateEmbedding(content);

  // Insert with embedding
  const result = await pool.query(
    `INSERT INTO intelligence.documents (title, content, metadata, embedding)
     VALUES ($1, $2, $3, $4::vector)
     RETURNING id`,
    [title, content, metadata, formatVector(embedding)]
  );

  return result.rows[0].id;
}

Document Chunking

Why Chunk Documents?

Large documents should be split into smaller chunks for better retrieval:

• Embeddings capture meaning better for shorter text
• Retrieval returns more relevant context
• Reduces noise in LLM responses

Chunking Function (SQL)

Create a PostgreSQL function for chunking:

-- deploy/schemas/intelligence/procedures/create_document_chunks.sql
CREATE FUNCTION intelligence.create_document_chunks(
    p_document_id INTEGER,
    p_chunk_size INTEGER DEFAULT 1000,
    p_chunk_overlap INTEGER DEFAULT 200
)
RETURNS VOID AS $$
DECLARE
    v_content TEXT;
    v_position INTEGER := 1;
    v_chunk_index INTEGER := 0;
    v_chunk TEXT;
    v_len INTEGER;
BEGIN
    SELECT content INTO v_content
    FROM intelligence.documents
    WHERE id = p_document_id;

    IF v_content IS NULL THEN
        RAISE NOTICE 'No content found for document_id %', p_document_id;
        RETURN;
    END IF;

    v_len := LENGTH(v_content);

    WHILE v_position <= v_len LOOP
        v_chunk := SUBSTRING(v_content FROM v_position FOR p_chunk_size);

        INSERT INTO intelligence.chunks (document_id, content, chunk_index)
        VALUES (p_document_id, v_chunk, v_chunk_index);

        v_position := v_position + (p_chunk_size - p_chunk_overlap);
        v_chunk_index := v_chunk_index + 1;
    END LOOP;
END;
$$ LANGUAGE plpgsql;

Chunking Parameters

Parameter	Recommended	Description
chunk_size	500-1000	Characters per chunk
chunk_overlap	100-200	Overlap between chunks

Overlap ensures context isn't lost at chunk boundaries.

Complete Ingestion Pipeline

import { Pool } from 'pg';
import { OllamaClient } from './utils/ollama';

const formatVector = (embedding: number[]): string => `[${embedding.join(',')}]`;

export class DocumentIngester {
  private pool: Pool;
  private ollama: OllamaClient;

  constructor(pool: Pool, ollamaBaseUrl?: string) {
    this.pool = pool;
    this.ollama = new OllamaClient(ollamaBaseUrl);
  }

  async ingestDocument(
    title: string,
    content: string,
    metadata: Record<string, unknown> = {},
    chunkSize: number = 1000,
    chunkOverlap: number = 200
  ): Promise<number> {
    // 1. Generate embedding for full document
    const docEmbedding = await this.ollama.generateEmbedding(content);

    // 2. Insert document
    const docResult = await this.pool.query(
      `INSERT INTO intelligence.documents (title, content, metadata, embedding)
       VALUES ($1, $2, $3, $4::vector)
       RETURNING id`,
      [title, content, metadata, formatVector(docEmbedding)]
    );
    const documentId = docResult.rows[0].id;

    // 3. Create chunks
    await this.pool.query(
      'SELECT intelligence.create_document_chunks($1, $2, $3)',
      [documentId, chunkSize, chunkOverlap]
    );

    // 4. Generate embeddings for each chunk
    const chunks = await this.pool.query(
      'SELECT id, content FROM intelligence.chunks WHERE document_id = $1 ORDER BY chunk_index',
      [documentId]
    );

    for (const chunk of chunks.rows) {
      const chunkEmbedding = await this.ollama.generateEmbedding(chunk.content);
      await this.pool.query(
        'UPDATE intelligence.chunks SET embedding = $1::vector WHERE id = $2',
        [formatVector(chunkEmbedding), chunk.id]
      );
    }

    return documentId;
  }
}

Testing Embeddings

import { getConnections, PgTestClient } from 'pgsql-test';
import { OllamaClient } from '../src/utils/ollama';

let pg: PgTestClient;
let teardown: () => Promise<void>;
let ollama: OllamaClient;

const formatVector = (embedding: number[]): string => `[${embedding.join(',')}]`;

beforeAll(async () => {
  ({ pg, teardown } = await getConnections());
  ollama = new OllamaClient();
});

afterAll(() => teardown());

test('should generate and store embedding', async () => {
  const text = 'Machine learning is a subset of artificial intelligence.';
  const embedding = await ollama.generateEmbedding(text);

  expect(embedding).toHaveLength(768); // nomic-embed-text dimensions

  const result = await pg.client.query(
    `INSERT INTO intelligence.documents (title, content, embedding)
     VALUES ($1, $2, $3::vector)
     RETURNING id`,
    ['ML Basics', text, formatVector(embedding)]
  );

  expect(result.rows[0].id).toBeDefined();
});

Design Considerations

Embeddings at Application Layer

Generate embeddings in your application, not in database triggers:

Why not triggers?

• HTTP calls in triggers can cause transaction timeouts
• Failed embedding calls would rollback the entire transaction
• Harder to retry or handle rate limits

Recommended approach:

• Generate embeddings in application code
• Use job queues for async processing if needed
• Handle failures gracefully with retries

Batch Processing

For large document sets, process in batches:

async function batchIngest(documents: Array<{title: string, content: string}>) {
  for (const doc of documents) {
    try {
      await ingester.ingestDocument(doc.title, doc.content);
      console.log(`Ingested: ${doc.title}`);
    } catch (error) {
      console.error(`Failed to ingest ${doc.title}:`, error);
      // Continue with next document
    }
  }
}

Troubleshooting

Issue	Solution
"Connection refused" to Ollama	Ensure Ollama is running: ollama serve
"Model not found"	Pull the model: ollama pull nomic-embed-text
Dimension mismatch	Ensure VECTOR(n) matches model output dimensions
Slow embedding generation	Consider batching or using a faster model
Memory issues	Process documents in smaller batches

References

• Related skill: pgvector-setup for database schema setup
• Related skill: pgvector-similarity-search for querying embeddings
• Related skill: ollama-integration for Ollama client details
• Related skill: rag-pipeline for complete RAG implementation