BloomFilterStat
Bloom filter - probabilistic set-membership test with no false negatives. bits bits are split across hashes positions per insert, derived from the hasher (default SplitMix64) via the Kirsch-Mitzenmacher double-hashing scheme.
False-positive rate is approximately (1 - e^(-hashes * n / bits))^hashes where n is the number of distinct inserts. Memory is bits / 64 Longs; mergeable element-wise via bitwise OR when bits and hashes match.
bits must be a power of two and a multiple of 64.
Use cases: membership queries with bounded memory; feature flags, deduplication of seen keys, "have we seen this user before". Tolerates false positives but never false negatives.
Memory: O(bits / 64) Longs, plus a totalSeen counter.
Update: O(hashes) per observation; hashes independent atomic OR ops.
Concurrency: Atomic OR on a striped Long array. Lock-free and exact under every Concurrency level; bit sets are idempotent and commutative.
Constructors
Properties
The thread-safety contract this stat was constructed with. Each stat picks the cell-encoding and lock strategy that honours this contract for its mathematical structure:
Mixer seeding the double-hashing scheme; defaults to SplitMix64.
Functions
Spawn a fresh accumulator with the same configuration. Optionally override the Concurrency; useful for materialising a wire spec at a different concurrency level than the source.
Fold another accumulator's snapshot into this one. The unit of merge is the immutable Result; not a live Stat; which is what lets the merge cross a process boundary. Many workers track slices of the same stream, call read periodically, ship snapshots to a coordinator, and the coordinator merges them in.
Materialise the current state as an immutable Result. Reads never mutate, so the caller can read as often as it likes without affecting the stream.
Reset the stat to its prior-seeded baseline. Equivalent to constructing a fresh stat with the same configuration, but in place; keeps the same Concurrency and any per-stat tunables.
Record an observation with the given weight, stamped at the current time.
Record an observation at timestampNanos with the given weight. Time matters for rate-shaped discrete stats; for cardinality / sketch stats the stamp is dropped.
BloomFilterStat
bits
concurrency
The thread-safety contract this stat was constructed with. Each stat picks the cell-encoding and lock strategy that honours this contract for its mathematical structure:
Concurrency.None: single-threaded; no synchronisation. Cheapest path.
Concurrency.Relaxed: lock-free best-effort. Multi-cell stats (Welford-style MeanStat, VarianceStat, MomentsStat) may drift under contention but never throw.
Concurrency.Strict: serialised when needed for full correctness across coupled cells. Sketches always self-serialise; Welford stats lock per update.
Concurrency.HighWrite: optimised for many concurrent writers; JVM uses striped adders for naively additive stats.
Picked at construction; immutable after.
create
Spawn a fresh accumulator with the same configuration. Optionally override the Concurrency; useful for materialising a wire spec at a different concurrency level than the source.
The returned stat is independent: its state starts at the configured baseline, not at the source's current state. Each modality subtype narrows the return type so chaining doesn't lose the modality.
hasher
Mixer seeding the double-hashing scheme; defaults to SplitMix64.
hashes
merge
Fold another accumulator's snapshot into this one. The unit of merge is the immutable Result; not a live Stat; which is what lets the merge cross a process boundary. Many workers track slices of the same stream, call read periodically, ship snapshots to a coordinator, and the coordinator merges them in.
Most stat families implement merge exactly (Chan-style parallel formulas for Welford, cell-wise additions for histograms, cell-wise max for HLL). SGD-based regressors merge approximately; they have no second-moment information for the principled combine. Each stat's KDoc documents its merge semantics.
read
Materialise the current state as an immutable Result. Reads never mutate, so the caller can read as often as it likes without affecting the stream.
Snapshot consistency depends on the configured Concurrency. Under Concurrency.Strict / Concurrency.HighWrite a read locks against writers so coupled cells stay consistent. Under Concurrency.Relaxed the cells race and the snapshot may drift by ULPs of the workload under heavy contention; the drift is bounded and the read never throws.
timestampNanos is the read timestamp. Stats that don't care about time silently drop it; stats that do (rates, decay families, recency, windowed wrappers) use it as the ordering signal.
reset
Reset the stat to its prior-seeded baseline. Equivalent to constructing a fresh stat with the same configuration, but in place; keeps the same Concurrency and any per-stat tunables.