Enum ProbeHoldUnavailableReason 

pub enum ProbeHoldUnavailableReason {
    Exhausted,
    Disabled,
    StakeLaneReserved,
}

Why a probe for a present blob got no eviction hold, as the reason label on decdn_probe_hold_unavailable_total.

Holds are best-effort, so this is not the same as “answered has_blob: false” — exhausted and stake_lane_reserved still advertise.

The three values are not interchangeable — each has a different operator remedy, which is why the reference DecdnProbeHoldViolations alert filters on reason="exhausted" alone. The derive renders variants in snake_case, so these encode as reason="exhausted" / "disabled" / "stake_lane_reserved".

Not to be confused with decdn_cache::ProbeHoldOutcome::Unavailable, which is the one probe-hold outcome that emits no metric at all — a blob genuinely absent is a true negative, not a refusal. The shared word is inverted between the two types: here it selects for the counter, there it selects against it.

Variants

Exhausted

Blob present, but all hold slots were live (max_probe_holds reached) — genuine budget pressure. The node still advertises has_blob: true and forgoes only the hold, so the blob may be LRU-evicted before the pull lands. This is the “raise max_probe_holds” signal and the only value the DecdnProbeHoldViolations alert fires on.

Disabled

Blob present, but the eviction-hold path is disabled by config (max_probe_holds == 0) — an intentional operator choice, not budget pressure (#739). The one reason that also suppresses the advertisement: the node answers has_blob: false for store-backed content (origin-held content takes no hold and is unaffected). Raising max_probe_holds is the remedy only if the disable was unintended; alerting on it would be nonsensical.

StakeLaneReserved

An end-client probe (a requester that is not a registered operator) hit the stake-lane-reserved end-client ceiling (max_probe_holds - cache.stake_lane_reserved_holds), keeping hold headroom for node-to-node cache-miss probes per ADR 003 §Admission and Priority (#757). The reservation is a content-independent admission decision, so unlike the two above it is decided before any hold attempt — but the handler still consults the cache afterwards to answer honestly, and advertises the blob if it is present. Zero unless cache.stake_lane_reserved_holds > 0.

Trait Implementations

impl Clone for ProbeHoldUnavailableReason

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for ProbeHoldUnavailableReason

impl Debug for ProbeHoldUnavailableReason

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for ProbeHoldUnavailableReason

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl EncodeLabelValue for ProbeHoldUnavailableReason

fn encode_label_value(&self) -> LabelValue<'_>

Borrows or copies self into a LabelValue.

impl Eq for ProbeHoldUnavailableReason

impl Hash for ProbeHoldUnavailableReason

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for ProbeHoldUnavailableReason

fn cmp(&self, other: &Self) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

fn clamp_to<R>(self, range: R) -> Self

where Self: Sized, R: ClampBounds<Self>,

🔬This is a nightly-only experimental API. (clamp_to)

Restrict a value to a certain range.

impl PartialEq for ProbeHoldUnavailableReason

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl PartialOrd for ProbeHoldUnavailableReason

fn partial_cmp(&self, other: &Self) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl Serialize for ProbeHoldUnavailableReason

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for ProbeHoldUnavailableReason