Batch Inference
Plain Explanation
Teams often need predictions for very large datasets, but serving one request at a time through a real-time endpoint can be slow and expensive at that scale. Daily product recommendations or periodic data refreshes don’t need instant answers, they need high throughput and predictable completion. That’s where batch inference helps: you run a job when needed, process a fixed input set, and avoid keeping servers running 24/7. A helpful picture is a mailroom: instead of sending letters one by one, you collect them into trays and hand them to sorting machines in waves. Batch inference does the same for data. A scheduled or on‑demand job pulls inputs from cloud storage, applies distributed preprocessing on CPUs, executes the model on GPUs, and writes results back to storage in bulk. This works because grouping inputs enables computation-level batching in the backend, which increases throughput, and frontends can also use request batching to reduce per-request overhead. Job runs can stream or partition reads and writes so the system doesn’t load the entire dataset into memory at once, keeping memory use stable while the pipeline progresses. Model loading and initialization are handled by the backend at job start, so the setup cost is paid once for the batch rather than per item.
Examples & Analogies
- E‑commerce recommendations refresh: An analytics team runs a nightly job to generate product recommendations for all users. The pipeline reads inputs from cloud storage, preprocesses on CPUs, batches predictions on GPUs, and writes the results back before the next day.
- Healthcare data analysis window: A provider analyzes a large daily batch of medical data during a scheduled window. The job streams data from storage, applies preprocessing, runs GPU inference, and emits outputs without loading the entire dataset into memory at once.
- Corpus‑wide embeddings generation: A team kicks off an on‑demand job to produce text embeddings for a large document set. It performs distributed read and preprocessing, batches embedding inference on GPUs, and writes vectors back to storage for later search.
At a Glance
| Batch inference (offline) | Real-time endpoint | Real-time endpoint with request batching | |
|---|---|---|---|
| Trigger | Schedule or on‑demand job | Direct user/event request | Direct user/event request |
| Resource model | Burst compute, then scale to zero | Always-on to meet SLOs | Always-on to meet SLOs |
| Latency target | Minutes to hours for a whole run | Milliseconds–seconds per call | Slightly higher per-call latency than pure real-time |
| Data access | Distributed read/preprocess/write from storage | Small per-request payloads | Small payloads grouped by the server |
| Throughput tactics | Computation-level batching in backend | Optimize per-request path | Request batching + backend batching |
| Startup behavior | Model loading/initialization at job start | Kept hot to avoid startup cost | Kept hot; batching improves utilization |
Teams often combine modes: offline jobs handle bulk datasets while real-time endpoints use request batching to lift throughput, with model loading and initialization shaping the actual latency/throughput trade-off.
Where and Why It Matters
- When immediate answers aren’t needed: Jobs run on a schedule or on demand, then shut down, aligning compute time with work and reducing idle cost.
- Mixed CPU–GPU pipelines: Distributed read and preprocessing on CPUs feed GPU model execution and distributed writes, enabling end-to-end scaling across the cluster.
- Frontends and backends coordinate batching: Request batching at the frontend and computation-level batching in the backend raise throughput without changing the model’s predictions.
- Memory-friendly data handling: Streaming or partitioned reads/writes avoid loading entire datasets into memory, making large batches feasible.
- Operational practice shift: Job orchestration systems provide queues, schedules, and monitoring to run discrete batch workloads reliably in production.
Common Misconceptions
- ❌ Myth: “Batch jobs must load the full dataset into memory.” → ✅ Reality: Distributed and streaming reads let the pipeline process data in parts without loading it all at once.
- ❌ Myth: “There’s no setup overhead in batch.” → ✅ Reality: Backends still load and initialize models; plan job windows to account for initialization and queue times.
- ❌ Myth: “Real-time is always worse for throughput.” → ✅ Reality: Real-time endpoints can use request batching to improve throughput, though they must remain online to meet latency goals.
How It Sounds in Conversation
- "Let’s schedule the batch inference window after ETL so inputs are ready in cloud storage."
- "We’ll use distributed read and preprocessing to feed the GPU stage without blowing up memory."
- "Enable request batching on the serving side and keep a computation-level batch in the backend to maximize throughput."
- "Because the job is offline, we can scale to zero after write-out; monitor completion and retries in the job queue."
- "Remember the model loading/initialization time at start; the SLA is for end-to-end job duration, not single-call latency."
Related Reading
References
- Batch inference — Ray 2.55.1
Notebook example with distributed read/write and notes on memory-efficient streaming execution.
- End-to-end: Offline Batch Inference
Shows offline batch pipelines: distributed read, preprocessing, GPU inference, and write.
- Run LLM batch inference on Anyscale
잡 기반 배치 추론 실행, 큐·스케줄·모니터링 개요.
- What is batch inference? How does it work?
Defines batch inference, schedule/on-demand triggers, and scale-to-zero contrast with real-time.
- Components of an AI inference stack
Explains end user app, inference frontend (request batching), and backend (compute batching, model init).
- Architecture overview — Ray Serve LLM
Covers serving primitives, request routing, and scaling considerations relevant to inference backends.