docs(effect-otel): design the flush-shape counters and batch-size histogram (RIG-3694) - #1224
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…togram (RIG-3694)
Design only; the implementation follows against this frozen record.
RIG-3694 asks whether turn coalescing produces many tiny batches or
saturates the cap. No existing instrument answers it: the twelve metrics in
Decision 2 count losses, retries, and depths, and a raw batch rate is
uninterpretable without knowing WHY each batch flushed.
The filed size/timer/shutdown taxonomy does not survive contact with the
code. The spine has no timed flush: pumpLoop's only idle wait is the wake
latch, the sole Effect.sleep is the priority-retry backoff, and takeBatch
never waits for a fuller batch. A reason="timer" label could never be
incremented, and an inert label is forbidden, so it is excluded.
The code-true taxonomy is four reasons, not three: full (the cap closed the
batch), drain (teardown residue), short (1..255 queued, the coalescing signal),
and empty. The empty case is reachable and was missed in drafting: a stale
coalesced wake exits the idle loop with both lanes empty, and the terminal
guard returns only when `ended`, so takeBatch produces a zero-frame batch and
the spine opens a stream carrying nothing. takeBatch has no empty guard.
Counting it separately keeps the other three honest -- folded into short it
would inflate the tiny-batch rate that is precisely the signal this issue
wants, making a wasted round trip look like aggressive coalescing.
Adds a batch-size histogram, the first in this module. Effect requires an
explicit boundary spec; MetricBoundaries.exponential({start:1,factor:2,
count:10}) gives [1,2,4,8,16,32,64,128,256] plus +Inf, verified by executing
it rather than reading the types. Power-of-two buckets hold constant relative
resolution where the variation is, the top boundary lands exactly on
PUBLISH_BATCH_MAX so saturation is one bucket delta, and +Inf stays
structurally empty as an invariant check.
Purely additive: Decision 2's rows and prose are untouched, following the
Decision 3a precedent in compass-agent-loop-otel. The freeze protects decision
content, and this rewrites none.
Ledger-impact: none
Co-authored-by: Matt Wilkinson <matt@rigel.build>
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Design only; the implementation follows against this frozen record.
RIG-3694 asks whether turn coalescing produces many tiny batches or
saturates the cap. No existing instrument answers it: the twelve metrics in
Decision 2 count losses, retries, and depths, and a raw batch rate is
uninterpretable without knowing WHY each batch flushed.
The filed size/timer/shutdown taxonomy does not survive contact with the
code. The spine has no timed flush: pumpLoop's only idle wait is the wake
latch, the sole Effect.sleep is the priority-retry backoff, and takeBatch
never waits for a fuller batch. A reason="timer" label could never be
incremented, and an inert label is forbidden, so it is excluded.
The code-true taxonomy is four reasons, not three: full (the cap closed the
batch), drain (teardown residue), short (1..255 queued, the coalescing signal),
and empty. The empty case is reachable and was missed in drafting: a stale
coalesced wake exits the idle loop with both lanes empty, and the terminal
guard returns only when
ended, so takeBatch produces a zero-frame batch andthe spine opens a stream carrying nothing. takeBatch has no empty guard.
Counting it separately keeps the other three honest -- folded into short it
would inflate the tiny-batch rate that is precisely the signal this issue
wants, making a wasted round trip look like aggressive coalescing.
Adds a batch-size histogram, the first in this module. Effect requires an
explicit boundary spec; MetricBoundaries.exponential({start:1,factor:2,
count:10}) gives [1,2,4,8,16,32,64,128,256] plus +Inf, verified by executing
it rather than reading the types. Power-of-two buckets hold constant relative
resolution where the variation is, the top boundary lands exactly on
PUBLISH_BATCH_MAX so saturation is one bucket delta, and +Inf stays
structurally empty as an invariant check.
Purely additive: Decision 2's rows and prose are untouched, following the
Decision 3a precedent in compass-agent-loop-otel. The freeze protects decision
content, and this rewrites none.
Ledger-impact: none
Co-authored-by: Matt Wilkinson matt@rigel.build