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 queue + worker configuration
• litestar workers run — CLI to start workers in-process or as a separate process
• 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]
• Consumer Litestar app modules MAY use from __future__ import annotations — canonical Litestar apps do.
• 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).
• Task params after * are keyword-only.

Quick Reference

Plugin Setup (canonical pattern)

The canonical pattern from litestar-fullstack-spa/src/py/app/server/plugins.py uses lazy initialization and use_server_lifespan=True so workers share the app's lifespan with the web process:

# Branch A — SAQ with Redis as the broker (pick when Redis is already in-stack
# for cache / sessions, or when you want the SAQ web UI + multi-queue fanout).
from litestar_saq import SAQConfig, SAQPlugin, QueueConfig, CronJob

from app.lib.settings import get_settings


def create_saq_plugin() -> SAQPlugin:
    settings = get_settings()
    return SAQPlugin(
        config=SAQConfig(
            dsn=settings.redis.url,              # redis://... — Redis broker
            use_server_lifespan=True,            # workers run inside web process by default
            web_enabled=settings.saq.web_enabled,
            queue_configs=[
                QueueConfig(
                    name="default",
                    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()

# Branch B — SAQ with PostgreSQL as the broker (pick when the project is
# PG-only, you want one less piece of infra, or throughput is moderate).
def create_saq_plugin_pg() -> SAQPlugin:
    settings = get_settings()
    return SAQPlugin(
        config=SAQConfig(
            dsn=settings.database.url,           # postgresql+asyncpg://... — PG broker
            use_server_lifespan=True,
            web_enabled=settings.saq.web_enabled,
            queue_configs=[
                QueueConfig(
                    name="default",
                    tasks=["app.domain.system.tasks.send_email"],
                ),
            ],
        ),
    )

Pick Branch A (SAQ + Redis) when: Redis is already in-stack (cache, sessions, Channels), you need multi-queue fanout across many workers, want the SAQ web UI and dead-letter dashboards, or have high throughput (>1k jobs/s per queue).

Pick Branch B (SAQ + PostgreSQL) when: PG-only deployment (Cloud SQL, AlloyDB, self-hosted single DB), avoiding extra infra, moderate throughput (<1k jobs/s), or you want jobs and business data in the same transactional boundary.

Pick Branch C (custom PG-native, no SAQ) when: you need pg_notify wake-ups with zero polling lag, FOR UPDATE SKIP LOCKED atomic task claim, or multi-target execution routing (local / cloudrun / immediate) — and you're willing to own a thin TaskService + WorkerPlugin pair. See below.

Anti-pattern: hard-coding dsn=settings.redis.url in a PG-only project just because Redis is the "default" example. Match the broker to the stack.

Branch C — Custom PostgreSQL-native queue (no SAQ)

Some projects reject SAQ entirely in favor of a thin TaskService + WorkerPlugin pair directly over PostgreSQL. This wins when you want FOR UPDATE SKIP LOCKED for atomic task claiming, pg_notify wake-ups (no polling lag), and multi-target execution routing (local / cloudrun / immediate) with zero extra dependencies beyond your existing Postgres connection.

The canonical example is the dma/accelerator codebase, which implements this pattern throughout. The WorkerPlugin wires task discovery and the in-process worker into the Litestar app lifecycle; the @task decorator registers callables and optional cron schedules; TaskService.create_task persists tasks to a job table. Canonical references: dma/accelerator/src/py/dma/utils/worker/plugin.py:L57–224 and dma/accelerator/src/py/dma/lib/jobs.py:L792–903.

See references/postgresql-native.md for the full pattern.

# NOTE: do NOT use `from __future__ import annotations` in modules that define
# @task-decorated functions — the decorator inspects signatures at registration time.

from app.lib.worker.jobs import task


@task(cron="0 2 * * *", timeout=120)
async def nightly_cleanup() -> None:
    """Purge soft-deleted records every night at 02:00 UTC."""
    ...


@task(priority=5, retries=1, timeout=300, execution_target="cloudrun")
async def generate_report(*, report_id: int) -> None:
    """Export report — runs on Cloud Run for isolation."""
    ...


# Enqueue imperatively (from a handler or service):
await generate_report.enqueue(execution_target="cloudrun", report_id=42)

Wire into Litestar

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

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

Define a Task

# app/domain/system/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 (queue, job, app-state).
        recipient: To address.
        subject: Email subject.
        body: Email body.
    """
    email_service = ctx["state"]["email_service"]
    await email_service.send(recipient, subject, body)

Enqueue from a Handler (DI of TaskQueues)

from litestar import Controller, post
from litestar_saq import TaskQueues


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

    @post("/")
    async def queue_notification(
        self,
        data: NotificationCreate,
        task_queues: TaskQueues,
    ) -> dict[str, str]:
        queue = task_queues.get("default")
        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"}

CLI

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

# Run workers in a separate process (production)
litestar --app app:app workers run --process

# 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

Option	Default	Use
timeout	None	Always set — bound how long a job can run
retries	0	Retry count on exception
ttl	600	Seconds to retain result after completion
key	None	Deduplication key — skip if already queued
heartbeat	0	Heartbeat interval for long-running jobs
scheduled	0	Unix timestamp to delay start

<workflow>

Workflow

Step 1: Install

pip install litestar-saq

Step 2: Define Queues

Build QueueConfig instances for each logical queue ("default", "emails", "reports"). Reference task functions by dotted path; the plugin imports them at startup.

Step 3: Configure Plugin

Wrap QueueConfigs in SAQConfig with the broker DSN. Pick Redis (redis://...) when Redis is already in the stack; pick PostgreSQL (postgresql+asyncpg://...) when the project is PG-only. Both brokers are fully supported — see Plugin Setup above for both patterns. Set use_server_lifespan=True so workers run inside the web process by default. Toggle web_enabled for the introspection UI.

Step 4: Define Tasks

Place task functions in app/domain/<domain>/tasks.py. First arg ctx: dict, rest keyword-only. Pull shared resources (DB, HTTP client, email service) from ctx["state"].

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", ...). 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/references/websockets.md.

Step 8: Run

For dev: litestar run (workers + web in one process via use_server_lifespan=True). For production: litestar workers run --process separately from litestar run.

</workflow> <guardrails>

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 — default is no timeout; a hung task pins a worker slot forever.
• Use heartbeat for jobs that run longer than ~30s, otherwise SAQ may mark them stuck and re-queue.
• 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.
• Use key= for deduplication — same logical job (per-user sync, per-resource refresh) should not stack.
• use_server_lifespan=True for dev and small-to-mid apps (workers inside the web process). Switch to --process for high-throughput production.
• Publish to Litestar Channels from tasks when the job result must update connected websocket clients. See ../litestar/references/websockets.md.
• Pull shared resources from ctx["state"], not module-level globals — keeps tests deterministic and supports per-worker init.
• Reach for a custom PG-native queue instead of SAQ when you need pg_notify wake-ups, FOR UPDATE SKIP LOCKED atomic claim, or execution-target routing across Cloud Run / local. For every other PG-only case, SAQ+PG is the simpler default. See references/postgresql-native.md.

</guardrails> <validation>

Validation Checkpoint

Before delivering Litestar + SAQ code, verify:

• SAQPlugin is in app.plugins
• SAQConfig.use_server_lifespan is set explicitly
• Each QueueConfig lists tasks by dotted path; the imports resolve
• All tasks have ctx: dict as the first positional arg, keyword-only params after *
• Every task has timeout set
• Long-running jobs (>30s) have heartbeat set
• CronJobs have timeout and a sensible cron expression
• Handlers enqueue via injected TaskQueues, not module globals
• Job dedup uses key= where applicable
• Production deploys run workers as a separate process (litestar workers run --process)

</validation> <example>

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.

# app/server/plugins.py
from litestar_saq import SAQConfig, SAQPlugin, QueueConfig, CronJob

from app.lib.settings import get_settings


def create_saq_plugin() -> SAQPlugin:
    settings = get_settings()
    return SAQPlugin(
        config=SAQConfig(
            dsn=settings.redis.url,          # Redis broker — swap for settings.database.url in PG-only stacks
            use_server_lifespan=True,
            web_enabled=settings.saq.web_enabled,
            queue_configs=[
                QueueConfig(
                    name="default",
                    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()

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


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

# app/domain/notifications/controllers.py
from litestar import Controller, post
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: TaskQueues,
    ) -> dict[str, str]:
        queue = task_queues.get("default")
        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"}

# 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],
)

# Dev: workers + web in one process
litestar --app app:app run

# Prod: separate worker process
litestar --app app:app workers run --process

</example>

---

References Index

• Advanced Patterns — Heartbeat tuning, dead-letter handling, job chaining, queue priorities, worker lifecycle hooks, Postgres backend.
• PostgreSQL-Native Queue (no SAQ) — TaskService + WorkerPlugin pattern from dma/accelerator: FOR UPDATE SKIP LOCKED claim, pg_notify wake-ups, @task decorator + ScheduleConfig cron registry, execution_target routing (local / cloudrun / immediate).

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
• https://github.com/tobymao/saq
• https://saq-py.readthedocs.io/en/latest/

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.