Litestar Saq

litestar-saq

litestar-saq is the first-party plugin that integrates SAQ (Simple Async Queue) with Litestar. It provides:

• SAQPlugin — registers queues, workers, lifespan management, and DI for TaskQueues
• SAQConfig / QueueConfig — declarative plugin, queue, worker, broker, shutdown, polling, and OpenTelemetry configuration
• litestar workers run — CLI to start worker processes, optionally filtered by queue
• Optional web UI mounted under the Litestar app
• DI injection of TaskQueues into route handlers for ergonomic enqueueing

Code Style Rules

• Use PEP 604 unions: T | None, never Optional[T]
• Async all I/O — task bodies and enqueue calls are async def.
• First positional arg of every task is ctx: dict (the SAQ context dict).
• Pass job payload as keyword arguments so task signatures and enqueue calls stay explicit.
• Use NamedDependency[TaskQueues] for handler injection. TaskQueues is registered under the task_queues dependency key, and Litestar 2.24 deprecates implicit DI.

Quick Reference

Plugin Setup (canonical pattern)

The canonical pattern from litestar-fullstack (src/py/app/server/plugins.py) uses lazy initialization and use_server_lifespan=True so worker child processes start and stop with the Litestar server lifespan.

Redis broker: Use this when Redis is already in the stack or is the chosen SAQ backend:

from litestar_saq import CronJob, QueueConfig, SAQConfig, SAQPlugin

from app.lib.settings import get_settings


def create_saq_plugin() -> SAQPlugin:
    settings = get_settings()
    return SAQPlugin(
        config=SAQConfig(
            use_server_lifespan=True,
            web_enabled=settings.saq.web_enabled,
            enable_otel=None,
            queue_configs=[
                QueueConfig(
                    name="default",
                    dsn=settings.redis.url,
                    tasks=["app.domain.system.tasks.send_email"],
                    scheduled_tasks=[
                        CronJob(
                            function="app.domain.system.tasks.cleanup_sessions",
                            cron="*/15 * * * *",
                            timeout=120,
                        ),
                    ],
                ),
            ],
        ),
    )


saq_plugin = create_saq_plugin()

PostgreSQL broker: Install litestar-saq[psycopg] when PostgreSQL is the chosen backend:

from litestar_saq import QueueConfig, SAQConfig, SAQPlugin

from app.lib.settings import get_settings


def create_saq_plugin_pg() -> SAQPlugin:
    settings = get_settings()
    return SAQPlugin(
        config=SAQConfig(
            use_server_lifespan=True,
            web_enabled=settings.saq.web_enabled,
            queue_configs=[
                QueueConfig(
                    name="default",
                    dsn=settings.database.url,
                    tasks=["app.domain.system.tasks.send_email"],
                ),
            ],
        ),
    )

Choose the broker already supported by the deployment. PostgreSQL job writes use SAQ's own pool and transaction; they are not automatically atomic with writes made through an application ORM or SQL session.

Each QueueConfig accepts exactly one connection source: a supported redis://, postgresql://, or http:// dsn, or a supported broker_instance. Supplying both or neither raises ImproperlyConfiguredException. PostgreSQL requires litestar-saq[psycopg]; configure queue behavior with broker_options and connection/client construction with broker_instance_options.

Wire into Litestar

from litestar import Litestar
from app.server.plugins import saq_plugin

app = Litestar(
    route_handlers=[...],
    plugins=[saq_plugin],
)

Define a Task

Task functions live in app/domain/<domain>/tasks.py:

async def send_email(ctx: dict, *, recipient: str, subject: str, body: str) -> None:
    """Send an email as a background job.

    Args:
        ctx: SAQ context dict populated by worker hooks.
        recipient: To address.
        subject: Email subject.
        body: Email body.
    """
    email_service = ctx["email_service"]
    await email_service.send(recipient, subject, body)

For long-running work, set the job's heartbeat stale threshold and decorate the task with monitored_job() so the plugin signals its batched HeartbeatManager while the task runs. heartbeat is not an update interval: SAQ marks an active job stuck when its last touch is older than that threshold.

from litestar_saq import monitored_job


@monitored_job()
async def rebuild_index(ctx: dict, *, index_name: str) -> dict[str, str]:
    await run_rebuild(index_name)
    return {"status": "complete"}

Enqueue from a Handler (DI of TaskQueues)

from litestar import Controller, post
from litestar.di import NamedDependency
from litestar_saq import TaskQueues


class NotificationController(Controller):
    path = "/api/notifications"

    @post("/")
    async def queue_notification(
        self,
        data: NotificationCreate,
        task_queues: NamedDependency[TaskQueues],
    ) -> dict[str, str]:
        queue = task_queues.get("default")
        job = await queue.enqueue(
            "send_email",
            recipient=data.email,
            subject=data.subject,
            body=data.body,
            timeout=30,
            retries=2,
            key=f"notify-{data.email}",
        )
        return {"status": "queued" if job is not None else "duplicate"}

CLI

# Run workers (uses the same Litestar app)
litestar --app app:app workers run

# Run multiple worker processes
litestar --app app:app workers run --workers 4

# Run only selected queues in this worker service
litestar --app app:app workers run --queues emails --queues reports

# Inspect queues
litestar --app app:app workers status

Web UI

When web_enabled=True, the SAQ web UI is mounted under the Litestar app for queue introspection and job retry.

Job Options

Workflow

Step 1: Install

pip install litestar-saq
pip install "litestar-saq[psycopg]"  # PostgreSQL broker
pip install "litestar-saq[otel]"     # OpenTelemetry spans

Step 2: Define Queues

Build QueueConfig instances for each logical queue ("default", "emails", "reports"). Put exactly one of dsn or broker_instance on each QueueConfig. Reference task functions by dotted path or callable; the plugin imports dotted paths at startup.

Step 3: Configure Plugin

Wrap QueueConfigs in SAQConfig. Pick a supported broker DSN (redis://..., postgresql://..., or http://...) that matches the deployment. Set use_server_lifespan=True when the web process should own worker child processes. Toggle web_enabled / web_guards for the introspection UI and enable_otel for tracing.

Step 4: Define Tasks

Place task functions in app/domain/<domain>/tasks.py. Use ctx: dict as the first argument and pass job data as keywords. Add shared resources (DB, HTTP client, email service) in QueueConfig.startup / before_process hooks and read them from ctx.

Step 5: Schedule Cron Work

Add CronJob entries to QueueConfig.scheduled_tasks for recurring work. Always set timeout. Do not use external cron tools for work that belongs in the queue.

Step 6: Enqueue from Handlers

Inject TaskQueues into route handlers. Use task_queues.get("name") then await queue.enqueue("task_name", ...). The result is the new Job, or None when its unique key already exists; handle both outcomes. Use key= for deduplication.

Step 7: Publish to Channels (optional)

For real-time updates after a job completes, publish to Litestar Channels from inside the task. See ../litestar-realtime/references/websockets.md.

Step 8: Run

For dev: litestar run can start worker child processes when use_server_lifespan=True. For production: run litestar workers run --workers N as a separate service/process from litestar run. There is no --process flag in litestar-saq 0.8.0. For portable multi-process workers, configure each queue with dsn. Under spawn and forkserver, litestar-saq removes cached live broker objects from the child configuration and rebuilds them from that DSN.

Guardrails

• Use litestar-saq, not raw SAQ, in Litestar apps — the plugin handles DI, lifespan, CLI, and the web UI. Raw SAQ misses all of that.
• Always set timeout on tasks and CronJobs — SAQ defaults to 10s, which is rarely the correct production value.
• Pair heartbeat with monitored_job() for long-running jobs — heartbeat defines when a job is stale; it does not emit updates. Keep the stale threshold longer than the decorator signal interval and the heartbeat manager's flush cadence.
• Inject TaskQueues via DI — don't import a global queue inside handlers. The plugin owns the queue lifecycle.
• Use CronJob for scheduled work — not external cron. CronJobs participate in retries, timeouts, and observability.
• Handle queue.enqueue() returning None — an existing unique key prevents insertion, so do not report every enqueue attempt as newly queued.
• Use key= for deduplication — same logical job (per-user sync, per-resource refresh) should not stack. The key remains occupied until the stored job expires or is removed, including after terminal completion.
• use_server_lifespan=True for dev and small-to-mid apps that should start worker child processes with the web server. For high-throughput production, run litestar workers run --workers N as a separate service.
• Use dsn for portable multi-process workers — forkserver/spawn workers rebuild brokers from QueueConfig.dsn. A broker_instance-only queue works in the parent and under fork, but spawn preparation rejects it.
• Set graceful shutdown controls for long jobs — use shutdown_grace_period_s and, when needed, cancellation_hard_deadline_s on QueueConfig.
• Publish to Litestar Channels from tasks when the job result must update connected websocket clients. See ../litestar-realtime/references/websockets.md.
• Pull shared resources from ctx populated by QueueConfig hooks, not module-level globals — keeps tests deterministic and supports per-worker init.

Validation Checkpoint

Before delivering Litestar + SAQ code, verify:

• SAQPlugin is in app.plugins
• SAQConfig.use_server_lifespan is set explicitly
• SAQConfig.worker_processes or CLI --workers is set intentionally
• Each QueueConfig has exactly one of dsn or broker_instance
• Multi-process worker configs use dsn, not broker_instance only
• Each QueueConfig lists tasks by dotted path; the imports resolve
• All tasks have ctx: dict as the first positional arg and receive job data as keywords
• Every task has timeout set
• Long-running jobs have a heartbeat stale threshold longer than their update cadence
• Long-running task functions use monitored_job() when they need automatic heartbeats
• CronJobs have timeout and a sensible cron expression
• Handlers enqueue via injected TaskQueues, not module globals
• Handlers account for queue.enqueue() returning None for an existing unique key
• Job dedup uses key= where applicable
• Production deploys run workers as a separate service (litestar workers run --workers N)

Example

Task: A Litestar app with a default queue, an email task, a cleanup CronJob, and a handler that enqueues notifications. This example uses Redis as the SAQ broker; swap dsn=settings.redis.url for dsn=settings.database.url if the project is PG-only — see Quick Reference above for both patterns.

Plugin creation in app/server/plugins.py:

from litestar_saq import CronJob, QueueConfig, SAQConfig, SAQPlugin

from app.lib.settings import get_settings


def create_saq_plugin() -> SAQPlugin:
    settings = get_settings()
    return SAQPlugin(
        config=SAQConfig(
            use_server_lifespan=True,
            web_enabled=settings.saq.web_enabled,
            queue_configs=[
                QueueConfig(
                    name="default",
                    dsn=settings.redis.url,
                    startup="app.domain.system.tasks.worker_startup",
                    shutdown="app.domain.system.tasks.worker_shutdown",
                    tasks=[
                        "app.domain.system.tasks.send_email",
                        "app.domain.system.tasks.cleanup_sessions",
                    ],
                    scheduled_tasks=[
                        CronJob(
                            function="app.domain.system.tasks.cleanup_sessions",
                            cron="*/15 * * * *",
                            timeout=120,
                        ),
                    ],
                ),
            ],
        ),
    )


saq_plugin = create_saq_plugin()

Task definitions in app/domain/system/tasks.py:

async def worker_startup(ctx: dict) -> None:
    """Initialize shared resources for this worker."""
    ctx["email_service"] = create_email_service()
    ctx["db"] = create_database_client()


async def worker_shutdown(ctx: dict) -> None:
    """Dispose shared worker resources."""
    await ctx["db"].close()


async def send_email(ctx: dict, *, recipient: str, subject: str, body: str) -> None:
    """Send an email as a background job."""
    email = ctx["email_service"]
    await email.send(recipient, subject, body)


async def cleanup_sessions(ctx: dict) -> None:
    """Purge expired sessions every 15 minutes."""
    db = ctx["db"]
    await db.execute("DELETE FROM session WHERE expires_at < now()")

Controller enqueueing in app/domain/notifications/controllers.py:

from litestar import Controller, post
from litestar.di import NamedDependency
from litestar_saq import TaskQueues

from app.domain.notifications.schemas import NotificationCreate


class NotificationController(Controller):
    path = "/api/notifications"
    tags = ["Notifications"]

    @post("/")
    async def queue_notification(
        self,
        data: NotificationCreate,
        task_queues: NamedDependency[TaskQueues],
    ) -> dict[str, str]:
        queue = task_queues.get("default")
        job = await queue.enqueue(
            "send_email",
            recipient=data.email,
            subject=data.subject,
            body=data.body,
            timeout=30,
            retries=2,
            key=f"notify-{data.email}",
        )
        return {"status": "queued" if job is not None else "duplicate"}

Application entrypoint in app.py:

from litestar import Litestar

from app.domain.notifications.controllers import NotificationController
from app.server.plugins import saq_plugin


app = Litestar(
    route_handlers=[NotificationController],
    plugins=[saq_plugin],
)

Running in development (workers start with server lifespan) and production:

litestar --app app:app run
litestar --app app:app workers run --workers 4

References Index

• Advanced Patterns — Heartbeat tuning, dead-letter handling, job chaining, queue priorities, worker lifecycle hooks, Postgres backend.
• Sidecar Worker Pattern — optional application-owned worker architecture; it is not part of litestar-saq or SAQ.

Cross-References

• litestar — Litestar app initialization, plugins, and lifespan.
• litestar websockets reference — Publish from a SAQ task to Litestar Channels for real-time UI updates.

Official References

• https://github.com/litestar-org/litestar-saq/tree/v0.8.0
• https://pypi.org/project/litestar-saq/0.8.0/
• https://github.com/tobymao/saq/tree/v0.26.4

Shared Styleguide Baseline

• Use shared styleguides for generic language/framework rules to reduce duplication in this skill.
• General Principles
• Python
• Litestar
• Keep this skill focused on tool-specific workflows, edge cases, and integration details.