Eventium PostgreSQL

PostgreSQL event store backend for Eventium.

Overview

eventium-postgresql provides a production-grade event store backed by PostgreSQL. It uses the persistent library for type-safe database access and guarantees monotonically increasing global sequence numbers via LOCK IN EXCLUSIVE MODE.

API

postgresqlEventStoreWriter
  :: (MonadIO m)
  => SqlEventStoreConfig entity serialized
  -> VersionedEventStoreWriter (SqlPersistT m) serialized

Readers come from eventium-sql-common (re-exported):

sqlEventStoreReader       :: SqlEventStoreConfig entity serialized -> VersionedEventStoreReader (SqlPersistT m) serialized
sqlGlobalEventStoreReader :: SqlEventStoreConfig entity serialized -> GlobalEventStoreReader (SqlPersistT m) serialized

Usage

import Eventium.Store.Postgresql
import Database.Persist.Postgresql

main :: IO ()
main = runStdoutLoggingT $
  withPostgresqlPool connStr 10 $ \pool -> do
    -- Use defaultSqlEventStoreConfig for the standard schema
    let writer = postgresqlEventStoreWriter defaultSqlEventStoreConfig
        reader = sqlEventStoreReader defaultSqlEventStoreConfig
    flip runSqlPool pool $ do
      runMigration migrateSqlEvent
      -- writer and reader are ready to use

Setup

# Start PostgreSQL with docker-compose (from project root)
docker compose up -d

# Default connection settings (matching docker-compose.yaml):
# POSTGRES_HOST=127.0.0.1  POSTGRES_PORT=5432
# POSTGRES_USER=postgres   POSTGRES_PASSWORD=password
# POSTGRES_DBNAME=eventium_test

Concurrency

PostgreSQL uses LOCK table_name IN EXCLUSIVE MODE during writes. This ensures that auto-increment IDs are assigned in commit order, so concurrent readers always see a gapless, monotonically increasing global sequence.

Installation

dependencies:
  - eventium-core
  - eventium-postgresql
  - persistent-postgresql

Documentation

• Main README
• SQL Common
• Design

License

MIT -- see LICENSE.md