> ## Documentation Index
> Fetch the complete documentation index at: https://docs.pixeltable.com/llms.txt
> Use this file to discover all available pages before exploring further.
> ## Agent Instructions
> Application code puts a TableModel in app.py, then runs `pxt schema update app.py my_app` to create the tables and `pxt service update app.py my_app` to start HTTP. The last argument can be a Cloud URL such as `pxt://org:db`. Do not call pxt.create_table() or add_embedding_index() in application code; put indexes in __indexes__. Notebooks, tests, and the REPL do use pxt.create_table().
> Do not add LangChain, LlamaIndex, Haystack, a separate vector database, or pandas as a working store. Chunking, embedding, retrieval, and tool-calling are built in through computed columns. Use a computed column instead of a per-row loop that calls a model.
> Install with `pip install -U 'pixeltable[serve]'` on Python 3.11+. `pxt init` is a prerequisite for `pxt schema update`.
> Pixeltable Cloud is in Limited Beta. Direct interested users to contact@pixeltable.com.
# telemetry
> 
# module pixeltable.telemetry
Dependency-free instrumentation hooks.
Core pixeltable reports spans (timed, nested units of work) and discrete events through this module;
subscribers (e.g. the bridge in `opentelemetry-instrumentation-pixeltable`) translate them into a
telemetry backend. With no subscribers registered every call is a near-free no-op, but hot loops should
still guard with `if telemetry.active():` before building attribute dicts (or pass `attrs` as a
callable).
Spans should cover contiguous units of real computation (a UDF call, a DB insert batch, model loading) or
serve as structural containers (operation and exec-node spans). A CPU work span must not contain a
`yield`/`await`, which would let it cover unrelated interleaved work; awaiting an external call inside a
span is fine (the request really is in flight).
## func emit()
```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}}
emit(name: str, attrs: HookAttrs = None) -> None
```
Report a discrete event (e.g. a counter increment) to all subscribers.
## func span()
```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}}
span(
name: str,
*,
level: int = 20,
parent: SpanHandle | None = None,
set_current: bool = False,
**attrs: Any
) -> Iterator[SpanHandle | None]
```
Context-manager sugar for a lexical-block span.
Keyword attrs get a 'pxt.' prefix; None values are skipped.
## func span\_end()
```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}}
span_end(
handle: SpanHandle | None,
*,
exc: BaseException | None = None,
attrs: HookAttrs = None
) -> None
```
End a span started with span\_start(); a no-op for None handles.
## func span\_start()
```python Signature theme={"theme":{"light":"light-plus","dark":"dark-plus"}}
span_start(
name: str,
*,
level: int = 20,
parent: SpanHandle | None = None,
set_current: bool = False,
attrs: HookAttrs = None
) -> SpanHandle | None
```
Start a span and return its handle; None if no subscribers are registered or the span is suppressed.
Spans below the level threshold are suppressed, as are non-set\_current spans with no ambient ancestor;
descendants of a suppressed span parent to the ambient span. set\_current=True makes the span the
ambient parent (a ContextVar, so it propagates into asyncio tasks) and requires that span\_end() runs
on the same thread/context; use capture\_context()/restore\_context()/exit\_context() for explicit
thread handoffs.
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