Over the last few months of rebuilding my Rails muscle memory, I’ve been diving deep into AI memory systems and experimenting with embeddings. One of the biggest lessons I’ve learned is that the cost of building AI isn’t just in the model it’s in how you use it. Tokens, storage, retrieval these are the hidden levers that determine whether your AI stack remains elegant or becomes a runaway expense.
And here’s the good news: with Ruby on Rails, managing these complexities becomes remarkably simple. Rails has always been about turning complicated things into something intuitive and maintainable and when you pair it with LangChain, it feels like magic.
Understanding the Cost of Embeddings
Most people think that running large language models is expensive because of the model itself. That’s only partially true. In practice, the real costs come from:
- Storing too much raw content: Every extra paragraph you embed costs more in tokens, both for the embedding itself and for later retrieval.
- Embedding long texts instead of summaries: LLMs don’t need the full novel they often just need the distilled version. Summaries are shorter, cheaper, and surprisingly effective.
- Retrieving too many memories: Pulling 50 memories for a simple question can cost more than the model call itself. Smart retrieval strategies can drastically cut costs.
- Feeding oversized prompts into the model: Every extra token in your prompt adds up. Cleaner prompts = cheaper calls.
I’ve seen projects where embedding every word of a document seemed “safe,” only to realize months later that the token bills were astronomical. That’s when I started thinking in terms of summary-first embeddings.
How Ruby on Rails Makes It Easy
Rails is my natural playground for building systems that scale reliably without over-engineering. Why does Rails pair so well with AI memory systems and LangChain? Several reasons:
Migrations Are Elegant
With Rails, adding a vector column with PgVector feels like any other migration. You can define your tables, indexes, and limits in one concise block:
class AddMemoriesTable < ActiveRecord::Migration[7.1]
def change
enable_extension "vector"
create_table :memories do |t|
t.text :content, null: false
t.vector :embedding, limit: 1536
t.jsonb :metadata
t.timestamps
end
end
end
There’s no need for complicated schema scripts. Rails handles the boring but essential details for you.
ActiveRecord Makes Embedding Storage a Breeze
Storing embeddings in Rails is almost poetic. With a simple model, you can create a memory with content, an embedding, and metadata in a single call:
Memory.create!(
content: "User prefers Japanese and Mexican cuisine.",
embedding: embedding_vector,
metadata: { type: :preference, user_id: 42 }
) And yes, you can query those memories by similarity in a single, readable line:
Memory.order(Arel.sql("embedding <=> '[#{query_embedding.join(',')}]'")) .limit(5) Rails keeps your code readable and maintainable while you handle sophisticated vector queries.
LangChain Integration is Natural
LangChain is all about chaining LLM calls, memory storage, and retrieval. In Rails, you already have everything you need: models, services, and job queues. You can plug LangChain into your Rails services to:
- Summarize content before embedding
- Retrieve only the most relevant memories
- Cache embeddings efficiently for repeated use
Saving Money with Smart Embeddings
Here’s the approach I’ve refined over multiple projects:
- Summarize Before You Embed
Instead of embedding full documents, feed the model a summary. A 50-word summary costs fewer tokens but preserves the semantic meaning needed for retrieval. - Limit Memory Retrieval
You rarely need more than 5–10 memories for a single model call. More often than not, extra memories just bloat your prompt and inflate costs. - Use Metadata Wisely
Store small, structured metadata alongside your embeddings to filter memories before similarity search. For example, filter byuser_idortypeinstead of pulling all records into the model. - Cache Strategically
Don’t re-embed unchanged content. Use Rails validations, background jobs, and services to embed only when necessary.
When you combine these strategies, the savings are significant. In some projects, embedding costs dropped by over 70% without losing retrieval accuracy.
Why I Stick With Rails and PostgreSQL
There are many ways to build AI memory systems. You could go with specialized databases, microservices, or cloud vector stores. But here’s what keeps me on Rails and Postgres:
- Reliability: Postgres is mature, stable, and production-ready. PgVector adds vector search without changing the foundation.
- Scalability: Rails scales surprisingly well when you keep queries efficient and leverage background jobs.
- Developer Happiness: Rails lets me iterate quickly. I can prototype, test, and deploy AI memory features without feeling like I’m juggling ten different systems.
- Future-Proofing: Rails projects can last years without a complete rewrite. AI infrastructure is still evolving having a stable base matters.
Closing Thoughts
AI memory doesn’t have to be complicated or expensive. By thinking carefully about embeddings, summaries, retrieval, and token usage and by leveraging Rails with LangChain you can build memory systems that are elegant, fast, and cost-effective.
For me, Rails is more than a framework. It’s a philosophy: build systems that scale naturally, make code readable, and keep complexity under control. Add PgVector and LangChain to that mix, and suddenly AI memory feels like something you can build without compromise.
In the world of AI, where complexity grows faster than budgets, that kind of simplicity is priceless.