RDBMS & Vector DBs

If you’re running a RAG application with Postgres for metadata, a vector database like Pinecone or Weaviate for embeddings, and LangChain for orchestration — this guide shows how Pixeltable unifies all three.

Related use case: Backend for AI Apps

Concept Mapping

Your Database Stack	Pixeltable Equivalent
Postgres / MySQL for metadata	`pxt.create_table()` with typed columns
Pinecone / Weaviate / Chroma for embeddings	`add_embedding_index()` — built-in HNSW search
S3 for media files (referenced by URL)	`pxt.Image`, `pxt.Video`, `pxt.Document` native types
ORM (SQLAlchemy, Prisma)	`.select()`, `.where()`, `.order_by()`
LangChain `DocumentLoader`	`insert()`, `import_csv()`, import from S3
`RecursiveCharacterTextSplitter`	`document_splitter` iterator via `create_view()`
`retriever.get_relevant_documents()`	`.similarity()` + `.order_by()`
`create_retrieval_chain()`	Computed column with LLM call
Keeping Postgres and Pinecone in sync	Automatic — derived columns can’t go stale

Side by Side: RAG Pipeline

Load documents, chunk, embed, retrieve, and generate answers.

LangChain + Pinecone
Pixeltable

from langchain_community.document_loaders import PyPDFLoader
from langchain_text_splitters import RecursiveCharacterTextSplitter
from langchain_openai import OpenAIEmbeddings, ChatOpenAI
from langchain_pinecone import PineconeVectorStore
from langchain.chains import create_retrieval_chain
from langchain.chains.combine_documents import create_stuff_documents_chain
from langchain.prompts import PromptTemplate

# Load and chunk
documents = PyPDFLoader('report.pdf').load()
chunks = RecursiveCharacterTextSplitter(
    chunk_size=1000, chunk_overlap=200
).split_documents(documents)

# Embed and store in Pinecone
embeddings = OpenAIEmbeddings(model='text-embedding-3-small')
vector_store = PineconeVectorStore.from_documents(
    chunks, embeddings, index_name='my-index')
retriever = vector_store.as_retriever(search_kwargs={'k': 5})

# Build chain
prompt = PromptTemplate.from_template(
    'Answer based on context:\n{context}\n\nQuestion: {input}')
llm = ChatOpenAI(model='gpt-4o-mini', temperature=0)
rag_chain = create_retrieval_chain(
    retriever,
    create_stuff_documents_chain(llm, prompt))

result = rag_chain.invoke({'input': 'What were the key findings?'})
print(result['answer'])

Packages: langchain, langchain-openai, langchain-pinecone, pinecone-client, sqlalchemy

import pixeltable as pxt
from pixeltable.functions.openai import chat_completions, embeddings
from pixeltable.functions.document import document_splitter

docs = pxt.create_table('rag.docs', {
    'pdf': pxt.Document, 'source': pxt.String})

chunks = pxt.create_view('rag.chunks', docs,
    iterator=document_splitter(
        docs.pdf, separators='sentence,token_limit', limit=300))

chunks.add_embedding_index('text',
    string_embed=embeddings.using(model='text-embedding-3-small'))

@pxt.query
def retrieve(question: str, top_k: int = 5) -> pxt.Query:
    sim = chunks.text.similarity(string=question)
    return chunks.order_by(sim, asc=False) \
        .limit(top_k).select(chunks.text)

qa = pxt.create_table('rag.qa', {'question': pxt.String})
qa.add_computed_column(context=retrieve(qa.question))

@pxt.udf
def build_prompt(question: str, context: list[dict]) -> str:
    ctx = '\n\n'.join(c['text'] for c in context)
    return f'Answer based on context:\n{ctx}\n\nQuestion: {question}'

qa.add_computed_column(prompt=build_prompt(qa.question, qa.context))
qa.add_computed_column(response=chat_completions(
    messages=[{'role': 'user', 'content': qa.prompt}],
    model='gpt-4o-mini'))
qa.add_computed_column(
    answer=qa.response.choices[0].message.content)

docs.insert([{'pdf': 'report.pdf', 'source': 'annual_report'}])
qa.insert([{'question': 'What were the key findings?'}])
qa.select(qa.question, qa.answer).collect()

Packages: pixeltable, openai

What Changes

	LangChain + Pinecone	Pixeltable
New documents	Re-run chunking, embedding, and Pinecone upsert	`docs.insert([...])` — chunks, embeddings, and index update automatically
Infrastructure	Postgres + Pinecone account + API keys	Single local system, no external services
Sync issues	Postgres metadata and Pinecone vectors can drift	Impossible — derived columns are always consistent
Intermediate results	Ephemeral unless you add logging	Every column is stored and queryable: `qa.select(qa.context).collect()`
Versioning	Not built-in	`t.history()`, `pxt.create_snapshot()`
Swap providers	Rewrite chain with new provider classes	Change the model string — same pipeline

Common Patterns

Adding new documents

LangChain + Pinecone
Pixeltable

new_docs = PyPDFLoader('new_report.pdf').load()
new_chunks = splitter.split_documents(new_docs)
vector_store.add_documents(new_chunks)
# Also update Postgres metadata...

docs.insert([{'pdf': 'new_report.pdf', 'source': 'quarterly'}])

Filtering by metadata

Pinecone
Pixeltable

retriever = vector_store.as_retriever(
    search_kwargs={'k': 5, 'filter': {'source': 'annual_report'}})

sim = chunks.text.similarity(string=query)
results = (chunks
    .where((chunks.source == 'annual_report') & (sim > 0.3))
    .order_by(sim, asc=False).limit(5).collect())

Inspecting what was retrieved

LangChain
Pixeltable

result = rag_chain.invoke({'input': query})
print(result['context'])  # if available

qa.select(qa.question, qa.context, qa.answer).collect()

Next Steps

Backend for AI Apps

Full use case walkthrough

RAG Pipeline

Complete RAG system with chunking and retrieval

Chunk Documents

Control chunk size, overlap, and splitting strategies

Semantic Search

Search patterns and similarity queries

Welcome to Pixeltable

Core Concepts

How-To

Concept Mapping

Side by Side: RAG Pipeline

What Changes

Common Patterns

Adding new documents

Filtering by metadata

Inspecting what was retrieved

Next Steps

Backend for AI Apps

RAG Pipeline

Chunk Documents

Semantic Search

Welcome to Pixeltable

Core Concepts

How-To

​Concept Mapping

​Side by Side: RAG Pipeline

​What Changes

​Common Patterns

​Adding new documents

​Filtering by metadata

​Inspecting what was retrieved

​Next Steps

Backend for AI Apps

RAG Pipeline

Chunk Documents

Semantic Search

Concept Mapping

Side by Side: RAG Pipeline

What Changes

Common Patterns

Adding new documents

Filtering by metadata

Inspecting what was retrieved

Next Steps