Context
The estimate output mode (transmit_sketch = false, added in the msgpack-wire-format work) emits typed metric rows instead of sketch bytes:
- DDSketch / KLL → one Gauge per configured quantile (
quantile label)
- HLL → one cardinality Gauge
CMS and CountSketch emit nothing — their FrequencySketch::top_k() returns an empty slice (src/sketches/cms.rs, src/sketches/countsketch.rs).
Why
CMS / CountSketch are hash-counter matrices: they answer "estimate the count for a given key" but do not record which keys were seen, so they cannot enumerate the top-K highest-frequency keys.
What's needed
Attach a heavy-hitter tracker (Space-Saving / a Top-K heap) that maintains candidate hot keys at insert time, then have top_k(k) read it. asap_sketchlib already has building blocks (e.g. CountL2HH, and the hh_keys channel on the delta types) that could back this.
Until then, estimate mode is quantile + cardinality only; frequency sketches stay on the empty default (documented in Sketch::estimate).
Scope
asap-precompute-rs: wire a tracker into CMSWrapper / CountSketchWrapper, implement top_k, map to EstimatePoint { labels: [("key", …)], value } (see the docs/df-processor-topology.md "OTel convention" row).- Possibly a small
asap_sketchlib addition for the tracker.
Context
The estimate output mode (
transmit_sketch = false, added in the msgpack-wire-format work) emits typed metric rows instead of sketch bytes:quantilelabel)CMS and CountSketch emit nothing — their
FrequencySketch::top_k()returns an empty slice (src/sketches/cms.rs,src/sketches/countsketch.rs).Why
CMS / CountSketch are hash-counter matrices: they answer "estimate the count for a given key" but do not record which keys were seen, so they cannot enumerate the top-K highest-frequency keys.
What's needed
Attach a heavy-hitter tracker (Space-Saving / a Top-K heap) that maintains candidate hot keys at insert time, then have
top_k(k)read it.asap_sketchlibalready has building blocks (e.g.CountL2HH, and thehh_keyschannel on the delta types) that could back this.Until then,
estimatemode is quantile + cardinality only; frequency sketches stay on the empty default (documented inSketch::estimate).Scope
asap-precompute-rs: wire a tracker intoCMSWrapper/CountSketchWrapper, implementtop_k, map toEstimatePoint { labels: [("key", …)], value }(see thedocs/df-processor-topology.md"OTel convention" row).asap_sketchlibaddition for the tracker.