MnemosynePostgres

PostgreSQL + pgvector backend for Mnemosyne, the task-agnostic agentic memory library.

This library implements the Mnemosyne.GraphBackend behaviour, persisting the knowledge graph in PostgreSQL with vector similarity search powered by pgvector.

Installation

Add mnemosyne_postgres to your list of dependencies in mix.exs:

def deps do
  [
    {:mnemosyne_postgres, "~> 0.1.0"} # x-release-please-version
  ]
end

Setup

1. Enable pgvector

Ensure the pgvector extension is available in your PostgreSQL instance (v0.5+).

2. Create a migration

defmodule MyApp.Repo.Migrations.AddMnemosyne do
  use Ecto.Migration

  def up, do: MnemosynePostgres.Migrations.up(version: 1, embedding_dimensions: 1536)
  def down, do: MnemosynePostgres.Migrations.down(version: 1)
end

Migration options

Option	Default	Description
:version	1	Target migration version
:embedding_dimensions	-- (required)	Dimensionality of your embedding vectors
:index_type	:hnsw	:hnsw or :ivfflat
:hnsw_m	pgvector default	Max connections per HNSW layer
:hnsw_ef_construction	pgvector default	Dynamic candidate list size for HNSW
:ivfflat_lists	pgvector default	Number of inverted lists for IVFFlat
:prefix	"mnemosyne_"	Table name prefix

3. Configure the backend

Set the default backend in your supervision tree so you don't repeat it on every open_repo call:

children = [
  {Mnemosyne.Supervisor,
    config: config,
    llm: MyApp.LLM,
    embedding: MyApp.Embedding,
    backend: {MnemosynePostgres.Backend, repo: MyApp.Repo}}
]

Then open repos -- repo_id is injected automatically from the first argument:

# Single-tenant (tenant_id defaults to "default")
{:ok, _pid} = Mnemosyne.open_repo("my-project")

# Multi-tenant
{:ok, _pid} = Mnemosyne.open_repo("my-project", tenant_id: "org-123")

Backend options

Option	Default	Description
:repo	-- (required)	Your Ecto repo module
:tenant_id	"default"	Tenant identifier for multi-tenant isolation
:prefix	"mnemosyne_"	Table name prefix (must match migration)

Storage Model

Nodes are stored in a single polymorphic nodes table with JSONB data, vector embeddings, and JSONB link maps. Metadata lives in a separate node_metadata table.

nodes                          node_metadata
+-----------+-----------+      +-------------+----------+
| id (uuid) | type      |      | node_id     | accessed |
| data      | embedding |      | reward      | recency  |
| links     | tenant_id |      | frequency   |          |
| repo_id   | inserted  |      +-------------+----------+
+-----------+-----------+

Vector indexes (HNSW or IVFFlat) are created per node type via partial indexes, avoiding the performance penalty of post-filtering across the full table.

Versioned Migrations

When a new schema version is released, create a new migration pointing to the next version:

defmodule MyApp.Repo.Migrations.UpgradeMnemosyneV2 do
  use Ecto.Migration

  def up, do: MnemosynePostgres.Migrations.up(version: 2, embedding_dimensions: 1536)
  def down, do: MnemosynePostgres.Migrations.down(version: 2)
end

The migration system tracks the current version via table comments and runs only the deltas.

Telemetry

All backend operations emit [:mnemosyne_postgres, ...] telemetry events. See MnemosynePostgres.Telemetry for the full list of events and their measurements.