Today we're excited to announce that **executable UDFs are now available
in public beta on ClickHouse Cloud**. You can write a function in Python, upload it as a zip to your cluster, and call it from
SQL like any built-in. ClickHouse manages a pool of long-lived sandboxed
processes and routes rows through them at query speed. The function is
callable anywhere SQL is: ad-hoc queries, joins, even materialized views
that fire on every insert.

This isn't a brand-new idea. We've shipped executable UDFs in self-hosted
ClickHouse for a while. [Our 2023 post on calling OpenAI from
SQL](https://clickhouse.com/blog/clickhouse-open-ai-user-defined-functions-udfs)
walked through the same mechanism. What's new today is that you don't
need to run your own server to use it. The model code lives where the
data is, runs in a managed sandbox, and the deployment surface is one
upload screen in the Cloud console.

To show what this unlocks, we built a demo. A small PyTorch autoencoder
scores ~6 billion equity trade ticks for anomalousness, inline with
ingest. A Next.js front-end consumes the embeddings. Full source for the
notebook, UDF bundle, SQL, and webapp is in [this repo](https://github.com/ClickHouse/stock-anomaly-udf).

![Anomaly dashboard with packedbubble chart and S&P 500 leaderboard](/uploads/hero_dashboard_5c8d3ce323.png)

## The problem this solves

You have a trained model. You have a stream of data in ClickHouse.
Getting them into the same room used to mean one of three options.

1. **Stand up a separate scoring service.** Now you maintain a model
   server, an ingest pipeline that routes rows to it, and a way to write
   the scores back into ClickHouse. The model is no longer near the data
   in any meaningful sense.

2. **Translate the model into pure SQL.** Workable for some tree-based
   models. Painful for anything with embeddings. Every retrain means
   regenerating thousands of lines of SQL by hand.

3. **Batch score offline and join later.** Loses freshness. The "anomaly"
   on a trade that just hit is only useful if you can react to it now.

Executable UDFs collapse all three into one. Write the inference code as
a normal Python file. Point ClickHouse at it. Call it from SQL. The
function runs inline with whatever query needs it, including inside a
materialized view, which is exactly what we do here.

## What we built

Last year we wrote ["Building StockHouse"](https://clickhouse.com/blog/building-stockhouse),
showing how ClickHouse handles a continuous firehose of stock trade ticks
in real time. That post stopped at the ingest and query layer. The
natural next question is: what if you wanted to apply a learned model to
every trade as it lands?

We picked an unsupervised anomaly-detection setup because it shows off
the shape of the problem cleanly.

- A small autoencoder (~270K parameters) is trained on 50M historical
  trade ticks. Its inputs: a hashed ticker, 7 numeric features (price,
  size, exchange, etc.), and 6 cyclical-encoded temporal features.
- For each trade, the model produces a **32-dim embedding** and a
  **reconstruction error**. High error means the model wasn't trained on
  patterns like this trade. It's *anomalous in shape* compared to what's
  normal for that symbol's history.
- The UDF that wraps this model is `embed_trade`. It's the only
  ML-specific piece in the system. Everything else is plain SQL: the
  score aggregation, the per-symbol baselines, the views.

Here's the data flow:

```
            ┌───────────────────────────┐
            │  default.trades           │     ← upstream feed (e.g. Polygon)
            └──────────────┬────────────┘
                           │ INSERT
                           ▼
            ┌───────────────────────────┐
            │  trades_embeddings_mv     │     ← fires on every INSERT
            │  (calls embed_trade UDF)  │
            └──────────────┬────────────┘
                           │
                           ▼
            ┌───────────────────────────┐
            │  default.trades_embeddings│     ← same trade + 32-dim
            │                           │       embedding + recon_score
            └──────────────┬────────────┘
              ▲            │
              │            │ refresh hourly
              │            ▼
              │  ┌──────────────────────┐
              │  │ trades_baselines     │     ← per-symbol score
              │  │ trades_dim_baselines │       distribution stats
              │  └──────────────────────┘
              │
              └──── consumed by webapp queries
                    (anomalies are defined relative
                     to each symbol's own baselines)
```

Every `INSERT INTO trades` flows through the materialized view, gets
scored, and lands in `trades_embeddings`. The webapp never re-runs the
model. It only reads `trades_embeddings` and two cheap baseline tables.
The expensive inference happens exactly once per trade, inline with
ingest, and every downstream query is a normal aggregation.

## Training the autoencoder

The model itself is small and unremarkable as ML goes, but the training
pipeline is worth a quick look because it has to produce artifacts the
UDF can load at runtime. The full walkthrough lives in
[`notebook/train_and_deploy_udf.ipynb`](https://github.com/ClickHouse/stock-anomaly-udf/blob/main/notebook/train_and_deploy_udf.ipynb).
A summary:

1. **Stream training data into Parquet chunks.** A SELECT against
   `default.trades` derives the 14 input features server-side (price,
   size, exchange, condition-code count, hashed ticker, and cyclical
   encodings of hour and day of week). The notebook pulls the result via
   `query_arrow_stream` and writes 5M-row Parquet chunks to local disk.
   Nothing is held in memory.

2. **Fit a `StandardScaler` incrementally.** Welford's algorithm via
   `partial_fit` gives the same mean and variance as a single
   `scaler.fit()` over the full dataset, with bounded memory. We fit on
   the 7 base numeric features only. The hashed ticker is an integer key
   and the cyclical features are already on a sensible scale.

3. **Train the autoencoder.** `TradeAutoencoderV2` is a 4-layer encoder
   into a 32-dim latent, with a symmetric decoder back to the numeric
   feature space. The sym embedding lookup happens at the input layer,
   `sym_idx = xxHash32(sym) % NUM_HASH_BUCKETS`. Loss is MSE on the
   reconstructed numeric features. Training streams rows out of the
   Parquet chunks via an `IterableDataset` and stops when a 200-batch
   moving-average loss fails to improve for 5 windows.

4. **Save two artifacts.** `scaler_params.pt` holds `mean_` and `scale_`
   as Float32 tensors. `trade_autoencoder_v2.pt` holds the model
   `state_dict` plus a `config` dict with the constructor kwargs. The
   UDF's `main.py` reads these at startup and reconstructs the model.

5. **Package the bundle.** A final notebook cell zips `main.py`,
   `requirements.txt`, and the two `.pt` files into `embed_trade.zip`,
   ready to upload.

## Deploying the UDF on Cloud

The deployment surface is a single upload screen in the Cloud console.
You give it a name, a zip containing your code and model files, and a
few runtime parameters.

![ClickHouse Cloud UDF deployment page with argument list and runtime settings](/uploads/cloud_udf_deployment_95cd9b3a7d.png)

For `embed_trade` we use:

- **Type:** `executable_pool`. Long-lived processes, hot model in memory.
- **Pool size:** `10` per replica. Each process loads the 2MB model at
  startup (~1.5s) and reuses it for every subsequent call.
- **Runtime:** `python3.11`. Dependencies (`torch==2.4.1`,
  `numpy==1.26.4`) come from the `requirements.txt` in the zip.
- **Format:** `TabSeparated`. The UDF reads one TSV line per input row
  on stdin and prints `(embedding, recon_score)` on stdout.
- **14 arguments**, each with an explicit ClickHouse type. The signature
  matches the autoencoder's training schema exactly. See
  [`udf/cloud-deployment.md`](udf/cloud-deployment.md) for the full
  table.

The function is then callable from SQL like any built-in:


The interesting part isn't *that* you can do this. It's *where* you can
put the call.

## Scoring every trade, inline with ingest

We wire `embed_trade` into a materialized view:



Every `INSERT INTO trades` fires this MV. The Python pool scores
the batch and lands the result in `trades_embeddings`. There's no other
mover, no other service, no separate scheduler. Just SQL.

This is the part that wasn't possible before executable UDFs landed in
Cloud. The equivalent service architecture would be a Kafka consumer
reading from `trades`, batching rows, posting to a model server, writing
the results back. Same end state, several more moving parts. Here it's
one DDL statement.

The performance shape is unsurprising. Cost per row is the model forward
pass (a few milliseconds on a warm pool) plus the TSV serialization.
ClickHouse batches rows into the UDF in chunks. The pool runs a handful
of in-flight invocations in parallel. We backfilled ~6B historical rows
at ~35K rows/sec sustained over several hours on a 3-replica cluster
with no manual scaling. Same UDF, same MV, same SQL.

## Making "anomalous" mean something

The autoencoder gives us a raw `recon_score` per trade. That's a number
between roughly 0.00002 and 1,000,000+ across the dataset. A naive
"trades above 0.062 are anomalous" filter (using the global 99th
percentile from the model's training distribution) sounds reasonable
until you actually look at the data.

A handful of symbols, like BRK.A and LLY, score every single trade above
that threshold because their share prices are unusually high. Their
entire distribution sits in the right tail of the global one. A "100%
anomalous" stat for those symbols is technically correct and practically
useless.

So we redefine "anomaly" relative to each symbol's own history. For
every symbol, we maintain its **lifetime p95 of `recon_score`**. A trade
is anomalous *for that symbol* if it exceeds the symbol's own p95. About
5% of trades qualify in a typical window, by construction. When that
fraction spikes well above 5%, the symbol is having a genuinely unusual
window.

The per-symbol baseline lives in another ClickHouse table:



A **refreshable materialized view** repopulates it every hour:

Refreshable MVs atomically truncate and replace the target table on each
refresh. Plain `MergeTree` is the right engine: no `FINAL`, no dedup
logic, no read-time overhead.

The leaderboard query then **joins live trades against the baselines
table** to count anomalies per symbol relative to their own baseline:

This query goes from ~1.7s (recomputing baselines inline as a CTE) to
~0.27s (joining against the pre-computed table). Same answer, roughly 6x
faster. The expensive part is materialized exactly once an hour instead
of on every page load.

## The webapp

The webapp is a Next.js + Click UI + Highcharts demo. It consumes
`trades_embeddings` and the baseline tables. 

**The anomaly dashboard** ranks S&P 500 symbols by share of trading
volume that exceeds their own baseline.

![Dashboard with bubble chart and detailed table](/uploads/hero_dashboard_5c8d3ce323.png)

The packed-bubble chart sizes and colors each symbol by `pct_of_volume`,
the share of total trading volume in the window that came from trades
above the symbol's lifetime p95. Symbols with redder, larger bubbles had
unusually anomaly-heavy windows. The table on the left carries the same
sort, with OHLC, max score, and the per-symbol baseline alongside.

**The symbol drilldown** zooms in on one ticker.

![Symbol drilldown showing candlesticks with volume bars and a table of anomalous trades](/uploads/symbol_drilldown_2844f51814.png)

A candlestick and volume pane sits on top. Both axes overlap a single
plot area, with the price axis stretched downward to push candles into
the top 65% and volume bars into the bottom 30%. Hover any row in the
anomalous-trades table and the corresponding candle's volume bar fills
yellow, sized to that trade's share of the bucket's total volume.
Crosshairs snap to the candle center.

**The similarity search** opens as a modal over the drilldown when you
click a trade.

![Similarity modal with radar chart and similar-trades table](/uploads/similarity_modal_80d0258023.gif)

The radar chart plots each trade's 13 input dimensions, normalized
against the symbol's lifetime min, max, and avg per dim. Because the avg
always maps to `0.5`, the baseline series renders as a perfect 13-sided
polygon at the chart's midpoint. Easy to spot deviations from. Hover a
similar-trade row to overlay it. The 50 most-similar trades come from
`cosineDistance(embedding, target_embedding)` over the same symbol's
embedding column.

**The model drift monitor** tracks the score distribution over time.

![Model drift weekly p50/p95/p99/max chart and per-symbol drift lines](/uploads/drift_monitor_f552fa5951.png)

Weekly p50, p95, p99, and max of `recon_score`, with horizontal
reference lines at the static thresholds the model was originally
calibrated against. If the p99 line starts climbing week over week, the
market has drifted from the model's training distribution and it's time
to retrain.

**The auction print monitor** is the home for the extreme tail. Opening
(c=12) and closing (c=15) auction prints score in the thousands to
millions because of their massive share sizes.

![Auction print monitor with top auctions table and daily counts chart](/uploads/auction_monitor_39b129720c.png)

They'd dominate every other view if we didn't filter them out everywhere
else. Here they get their own page.

## One more thing: network-access UDFs (private beta)

Everything you've seen so far runs on the deterministic path. `embed_trade`
scores rows at ingest, baselines refresh hourly, the webapp reads
pre-computed tables. No external calls anywhere on the read path. That's
the shape you want for the load-bearing pieces: cheap, predictable, no
upstream that can disappear on you.

But once a trade has been flagged as anomalous, the obvious next
question is *why*. That answer lives outside ClickHouse — in news APIs,
SEC filings, halt notices, social signals. To pull those in we need
network access from the UDF.

**Network-access executable UDFs are in private beta on ClickHouse
Cloud.** Once enabled, the UDF runtime can make outbound HTTPS calls to
any allowed host. We added two new UDFs in this repo to use it:

### `nearby_events`

Given `(sym, t, window_min)`, calls two external sources and returns a
JSON array of events near that trade time:

1. **Massive News API** (Polygon recently rebranded as **Massive**;
   `api.polygon.io` endpoints still respond as before).
2. **SEC EDGAR** (free, public, no API key).


You could *almost* do this with `url()`. The differences that make it a
UDF:

- **In-process composition.** Polygon's results and EDGAR's filings get
  deduped, sorted, and capped in a single Python call. Chaining two
  `url()` calls in SQL would force the same logic into a `UNION ALL`
  with downstream `arrayJoin`/`groupArray` plumbing — workable, but
  uglier.
- **Auth in env.** The Polygon API key is read from
  `POLYGON_API_KEY` at pool-process startup. It never appears in SQL.
- **Per-process LRU cache.** Each pool worker keeps recent results
  keyed by `(sym, minute, window)`. The same trade hovered twice in the
  UI costs one API call, not two.
- **Connection reuse.** A long-lived `requests.Session()` per process
  keeps HTTP connections alive for the duration of that worker, which
  is hours.

### `classify_trade`

Given `(sym, t)`, fetches context via `nearby_events`'s internals, then
asks **Anthropic Claude** to classify the most likely cause of the
anomalous trade. Returns a typed tuple:

The cause is constrained to a fixed taxonomy: `earnings`, `m_and_a`,
`halt`, `rumor`, `sector_move`, `block_trade`, `no_news_found`. We
enforce this via Anthropic's **tool-use** mechanism. The model is
required to call a tool whose `input_schema` includes an `enum` on the
`cause` field, so the response is guaranteed to be parseable and the
cause is guaranteed to be one of the known values. No regex parsing of
free-form prose, no "the model returned something close to 'earnings'
but with extra words" follow-up logic.

Remember the similarity modal from the webapp? `classify_trade` and
`nearby_events` drive a **"Why anomalous?"** panel pinned to the top of
that modal. When you open a trade, the panel hits both UDFs in parallel
and shows:

- A badge with the classified cause and a confidence number
- A 1–2 sentence summary written by the model
- A short list of the news headlines and filings that drove the call

![Similarity modal showing the Why-anomalous panel with cause badge, summary, and event list](/uploads/why_anomalous_ef01e5439a.png)

### Why this matters

`url()` has been in ClickHouse for years and it's good for ad-hoc
fetches. What network-access UDFs add is the rest of the picture:
stateful clients, auth lifecycle, multi-step pipelines, structured
LLM output, and per-process caching. The boundary between "code that
needs to run" and "data that needs to be queried" gets thinner.

You can put a 200-line Python function with three API calls and an LLM
prompt into a `SELECT`. Nobody else has to learn it exists.

**Want to try it on your cluster?** Network-access UDFs are in private
beta — reach out to ClickHouse Cloud support to get it enabled!

## What's interesting about this

Most ML-on-streaming-data architectures pay an integration tax. The
model lives somewhere. The data lives somewhere else. The glue between
them is its own system. The setup in this repo flattens that. There's a
ClickHouse Cloud cluster, a 2MB Python file, and one DDL statement that
binds them together.

Every piece of UI logic in the webapp is a SQL query. Anomaly detection
is the only ML in the system, and even that's not "ML in the webapp",
it's a column in a table. The "how anomalous is this symbol's last
hour" calculation, the "find me similar trades by cosine distance"
query, the per-symbol p95 baseline, the materialized views that keep it
all fresh: standard SQL features, running against standard ClickHouse
tables.

Executable UDFs in Cloud don't add new abstractions on top of
ClickHouse. They give you a way to make Python part of your SQL.

## Reproduce it

The full project is at <https://github.com/clickhouse/stock-anomaly-udf>.

```
stock-anomaly-udf/
├── notebook/   # Train the autoencoder, export weights, package the UDF zip
├── udf/        # The deployable bundle: main.py, model weights, deployment notes
├── sql/        # Source schema, the auto-embed MV, two refreshable baseline MVs
└── web/        # Next.js demo app
```

### Quickstart

1. **Get the UDF onto your cluster.**
   - Zip the contents of `udf/embed_trade/`:
     ```bash
     cd udf/embed_trade && zip embed_trade.zip main.py requirements.txt *.pt
     ```
   - Upload via the Cloud UDF deployment UI. Configure per
     [`udf/cloud-deployment.md`](https://github.com/ClickHouse/stock-anomaly-udf/blob/main/udf/cloud-deployment.md).

2. **Run the SQL files in order:**
   ```sql
   :run sql/01_source_schema.sql
   :run sql/02_embeddings_mv.sql
   :run sql/03_score_baselines.sql
   :run sql/04_dim_baselines.sql
   ```

3. **Backfill historical data** (optional). Bulk INSERT into
   `trades_embeddings` using the same SELECT pattern as the MV, scoped to
   any time range. The MV in step 2 will catch every subsequent INSERT
   into `default.trades` automatically.

4. **Start the webapp:**
   ```bash
   cd web
   cp .env.example .env.local   # fill in CH_HOST/PORT/USER/PASS/DB
   npm install
   npm run dev
   ```
   Open <http://localhost:3000>.

The notebook in `notebook/` walks through training your own autoencoder
end to end. It streams training data from `default.trades` into Parquet
chunks, fits a `StandardScaler` incrementally, trains with early
stopping, and zips the artifacts into a deployable bundle.

## Try executable UDFs

Public beta is live in ClickHouse Cloud today. Drop us a note if you put
something interesting together with it!

Interested in seeing how ClickHouse works on your data? Get started with ClickHouse Cloud in minutes and receive $300 in free credits.

Get started today

Today we're excited to announce that executable UDFs are now available in public beta on ClickHouse Cloud. You can write a function in Python, upload it as a zip to your cluster, and call it from SQL like any built-in. ClickHouse manages a pool of long-li

Kevin Zhang

Blog posts by Kevin Zhang

Executable UDFs are now in public beta on ClickHouse Cloud