Does Temporarity::Cumulative is just a memory leak? Where else this can happen?

[Ddystopia]

From the opentelemetry_sdk::metrics:

/// Defines the window that an aggregation was calculated over.
#[derive(Debug, Copy, Clone, Default, PartialEq, Eq, Hash)]
#[non_exhaustive]
pub enum Temporality {
    /// A measurement interval that continues to expand forward in time from a
    /// starting point.
    ///
    /// New measurements are added to all previous measurements since a start time.
    #[default]
    Cumulative,

    /// A measurement interval that resets each cycle.
    ///
    /// Measurements from one cycle are recorded independently, measurements from
    /// other cycles do not affect them.
    Delta,

    /// Configures Synchronous Counter and Histogram instruments to use
    /// Delta aggregation temporality, which allows them to shed memory
    /// following a cardinality explosion, thus use less memory.
    LowMemory,
}

Reading those docs it seems like with Cumulative data are just always appended and only Delta and LowMemory every remove data points. Do I understand it correctly? With Cumulative this memory won't be freed? Or is there a bound?

If it is indeed a leak... I read those docs by a coincidence, thus there must be similar design decisions. Could you please point me where I should change which defaults (Cumulative is the default) to make sure opentelemetry-rust won't leak anything? My service can't tolerate leaks and downtimes needed to reset the heap.

[cijothomas]

It is not really "leak". Cumulative is intended for systems like Prometheus, which expects them only.

Is there a bound
Cardinality capping is precisely for this (default 2000 metrics points per metric)

It is one-line to change from Cumulative to Delta https://github.com/open-telemetry/opentelemetry-rust/blob/main/examples/metrics-basic/src/main.rs#L9-L10
But this is often determined by the backend - if you use Prometheus like, then Cumulative is mandatory.

See the below doc which has a lot more detail on the topic:
https://github.com/open-telemetry/opentelemetry-rust/blob/main/docs/metrics.md