Struct ProfilingTagLayer 

pub struct ProfilingTagLayer;

👎Deprecated since 2.15.0:

inert: per-span pyroscope tagging leaked memory and emptied profiles; correlation returns with the OTLP profiles exporter

Inert. Was: a tracing layer that tagged the running pyroscope agent with trace_id/span_id on every span enter and exit.

Why this does nothing

Per-span tagging is not implementable against the pprof backend, and enabling it was strictly worse than having no correlation at all. In pyroscope-rs the backend’s own comment calls dump_report a “workaround for pprof-rs to interrupt the profiler”, and both Backend::add_tag and Backend::remove_tag call it unconditionally. One dump_report symbolises every entry currently in the collector — backtrace::resolve per frame, building a fresh Vec<Vec<Symbol>> with a String and a PathBuf per symbol — and then clears the collector.

So each span enter cost two full profile rebuilds, and each exit two more. Measured on a static-musl build at the shipped 100 Hz sample rate, driving spans from two threads:

t=10s  dumps=868726  clears=868725  sessions=1  collector_entries=0

~87,000 profile rebuilds per second against one 10-second upload. Two consequences, and the second is why this is not merely a tuning problem:

1. The allocation churn grew RSS without bound. Over 90 minutes on static musl the leak was 7.4 MiB/h with this layer and 1.0 MiB/h without, which matches the 6.5 MiB/h observed on brefwiz-spiffe in production, where it OOM-killed both replicas roughly every 5.5 hours against a 512Mi cgroup.
2. collector_entries=0 at every upload: the collector was cleared far faster than the 100 Hz sampler could fill it, so the profiles this layer existed to enrich were arriving essentially empty. The correlation feature destroyed the very data it annotated.

Sampling itself is not implicated — with tagging off, 63,254 samples over 420 seconds moved RSS by 0.03 MiB/h.

What replaces it

Nothing, on this backend: there is no bounded form. The cost is per tag call, so sampling spans or tagging only roots still buys full profile rebuilds at a fraction of the span rate, and each rebuild still truncates the sample window. Trace/profile correlation returns with the native OTLP profiles exporter this bridge is already sunset-bound against.

The type is kept, registered, and doing nothing so the subscriber stack and the public surface are unchanged; it is removed in the next major.

Trait Implementations

impl<S> Layer<S> for ProfilingTagLayer

where S: Subscriber + for<'a> LookupSpan<'a>,

Available on crate feature profiling-bridge-pyroscope-rs only.

fn on_register_dispatch(&self, subscriber: &Dispatch)

Performs late initialization when installing this layer as a Subscriber.

fn on_layer(&mut self, subscriber: &mut S)

Performs late initialization when attaching a Layer to a Subscriber.

fn register_callsite(&self, metadata: &'static Metadata<'static>) -> Interest

Registers a new callsite with this layer, returning whether or not the layer is interested in being notified about the callsite, similarly to Subscriber::register_callsite.

fn enabled(&self, metadata: &Metadata<'_>, ctx: Context<'_, S>) -> bool

Returns true if this layer is interested in a span or event with the given metadata in the current Context, similarly to Subscriber::enabled.

fn on_new_span(&self, attrs: &Attributes<'_>, id: &Id, ctx: Context<'_, S>)

Notifies this layer that a new span was constructed with the given Attributes and Id.

fn on_record(&self, _span: &Id, _values: &Record<'_>, _ctx: Context<'_, S>)

Notifies this layer that a span with the given Id recorded the given values.

fn on_follows_from(&self, _span: &Id, _follows: &Id, _ctx: Context<'_, S>)

Notifies this layer that a span with the ID span recorded that it follows from the span with the ID follows.

fn event_enabled(&self, _event: &Event<'_>, _ctx: Context<'_, S>) -> bool

Called before on_event, to determine if on_event should be called.

fn on_event(&self, _event: &Event<'_>, _ctx: Context<'_, S>)

Notifies this layer that an event has occurred.

fn on_enter(&self, _id: &Id, _ctx: Context<'_, S>)

Notifies this layer that a span with the given ID was entered.

fn on_exit(&self, _id: &Id, _ctx: Context<'_, S>)

Notifies this layer that the span with the given ID was exited.

fn on_close(&self, _id: Id, _ctx: Context<'_, S>)

Notifies this layer that the span with the given ID has been closed.

fn on_id_change(&self, _old: &Id, _new: &Id, _ctx: Context<'_, S>)

Notifies this layer that a span ID has been cloned, and that the subscriber returned a different ID.

fn and_then<L>(self, layer: L) -> Layered<L, Self, S>

where L: Layer<S>, Self: Sized,

Composes this layer around the given Layer, returning a Layered struct implementing Layer.

fn with_subscriber(self, inner: S) -> Layered<Self, S>

where Self: Sized,

Composes this Layer with the given Subscriber, returning a Layered struct that implements Subscriber.

fn with_filter<F>(self, filter: F) -> Filtered<Self, F, S>

where Self: Sized, F: Filter<S>,

Combines self with a Filter, returning a Filtered layer.

fn boxed(self) -> Box<dyn Layer<S> + Send + Sync>

where Self: Sized + Layer<S> + Send + Sync + 'static, S: Subscriber,

Erases the type of this Layer, returning a Boxed dyn Layer trait object.