Metric & Arrow Schema

Exact schema used when exporting Micrometer metrics as Apache Arrow.

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Supported Meter Types

All core Micrometer meters are supported:

• Counter
• Gauge
• Timer
• DistributionSummary
• LongTaskTimer
• FunctionCounter
• FunctionTimer

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Arrow Schema (Authoritative)

Each published metric is written as one Arrow row using the following schema:

name               STRING   NOT NULL
type               STRING   NOT NULL
application_id     STRING
application_name   STRING
application_host   STRING
tags               MAP<STRING, STRING> NOT NULL
value              DOUBLE
min                DOUBLE
max                DOUBLE
mean               DOUBLE

This schema is defined in ArrowMetricSchema and is stable across releases.

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Field Semantics

Field	Description
name	Metric name
type	Meter type (counter, timer, gauge, ...)
application_id	Logical application identifier
application_name	Human‑readable service name
application_host	Hostname or node id
tags	Micrometer tags as key‑value map
value	Primary metric value (count, gauge value, active tasks)
min	Minimum observed value (when applicable)
max	Maximum observed value
mean	Mean / average value

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Type‑Specific Mapping

Meter Type	value	min	max	mean
Counter	count	0	0	0
Gauge	value	0	0	0
Timer	count	0	max(sec)	mean(sec)
DistributionSummary	count	0	max	mean
LongTaskTimer	active tasks	0	total(sec)	avg(sec)
Function meters	computed	0	computed	computed

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Deterministic Output

The registry guarantees:

• Stable schema
• Deterministic ordering (sorted by type and name)
• Repeatable snapshots

This enables:

• CI regression checks
• Release comparisons
• Diff‑based validation