MongoDB

If your team already runs MongoDB, Recall can keep its memory there, on Atlas or your own servers. Every Recall capability works on it: typed facts, corrections, history, keyword search, cached reads, and agent resume, with agent writes committed in one transaction with their lease. No Atlas Search index is needed.

Before you start

MongoDB 6.0 or later. A replica set is recommended, and Atlas always is one; a single-node replica set is enough (see Good to know).
A user with readWrite on the database Recall uses.
recall 0.21.0 or later: brew install polign/tap/recall or pip install polign-recall.

Run the memory server on MongoDB

Start MongoDB as a single-node replica set, if you are not using Atlas:

docker run -d --name mongo -p 27017:27017 mongo:8.0 --replSet rs0 --bind_ip_all
docker exec mongo mongosh --eval 'rs.initiate({_id:"rs0",members:[{_id:0,host:"localhost:27017"}]})'

Add Recall to Claude Code as an MCP server:
```
claude mcp add recall \
  -e RECALL_BACKEND=mongodb \
  -e MONGODB_URI='mongodb://localhost:27017/recall?directConnection=true' \
  -- recall mcp -write
```
For Atlas, use the mongodb+srv:// connection string Atlas gives you; put the password in MONGODB_PASSWORD instead of the string if you prefer. Add -agent for the agent resume tools. Other MCP hosts take the same command and variables, or the flags recall -backend mongodb -url mongodb://... mcp -write.
Restart Claude Code and ask it to remember something. The first write creates the collection.

recall setup and the Recall plugin set up a polign_db connection. With MongoDB, add the MCP server yourself as in step 2.

Use it from Go

import (
	"github.com/Polign/recall"
	"github.com/Polign/recall/backend/mongodb"
)

backend, err := mongodb.New(mongodb.Config{
	URL: os.Getenv("MONGODB_URI"),
})
defer backend.Close()
client, err := recall.NewClient(recall.Config{
	Backend:    backend,
	Collection: "team_memory",
	Registry:   recall.DefaultRegistry(),
	Embedder:   recall.LexicalEmbedder{},
})

mongodb.Config also takes a Database (default: the connection string's path, then recall) and a Client to share a *mongo.Client you already have. The package uses the official MongoDB Go driver, which a program pulls in only by importing it.

What gets stored

Recall	MongoDB
A collection	A collection named `rc_` and the collection's name, created on the first write with the first vector's size
An event	A document: the event ID as `_id`, the vector, the metadata as JSON so it reads back exactly as written, and its scalar fields as `{k, v}` pairs for filtering
Indexes	A compound index on the metadata pairs, and a text index on the event text for keyword search
Bookkeeping	`recall_collections` maps each collection and counts its writes, which is what cached reads check; `recall_leases` holds agent leases

Metadata is filtered through the pairs rather than as document fields, so Recall's field names, which can contain dots, never turn into MongoDB paths.

Agent resume and fenced writes

Leases are documents in recall_leases, taken and renewed in one atomic update that judges expiry by the server's clock, so recall mcp -agent and Client.Resume work as they do on polign_db. On a replica set, each agent write commits in one transaction with a write to its lease document. A takeover that changes the lease conflicts with the in-flight write, so a process that stalled past its lease cannot land a late write over its successor's. See Resume for how actions and leases fit together.

Good to know

Vector search is exact: the similarity is computed in the server over the events a filter keeps, so the answer is the true nearest events with no search index to build. Agent memory collections hold thousands of events, where this is fast; it is not meant for collections of millions.
On a standalone server, which has no transactions, an agent write is checked against its lease just before it lands rather than with it, and a listing and its total are two reads. Run a replica set for agents.
A collection takes its vector size from the first write. Changing embedders needs a new collection.
Keyword search uses MongoDB's english text index, fixed when a collection is created.

If something goes wrong

What you see	What to do
`unknown backend "mongodb"`	Your `recall` is older than 0.21.0. Upgrade it.
`server selection error`	MongoDB is not reachable at that address. For a local single-node replica set, add `directConnection=true` to the connection string.
`connection string must start with mongodb:// or mongodb+srv://`	Check `MONGODB_URI`.
`holds 256-dimensional vectors, not 384`	The collection was created with another embedder. Use a new `-collection` when you change embedders.
`lease_held` on resume	Another process holds the agent, or one died less than a lease time ago. Wait for the lease to expire.

Source & license

The MongoDB backend is part of Recall, open source under the Apache License 2.0, in github.com/Polign/recall. Bug reports and pull requests go there.