meldotel

Meldbase OpenTelemetry metrics

meldotel bridges the latest immutable admin.Sampler snapshot to the stable OpenTelemetry Go Metrics API. It accepts an application-owned MeterProvider; it never constructs an SDK/exporter, uses the global provider, opens a network connection, starts a goroutine or calls DB.Stats() from an OTel callback.

sampler, err := admin.NewSampler(db, admin.SamplerOptions{
    Interval: time.Second,
    Server:   handler, // optional aggregate server/RPC/Worker metrics
})
if err != nil {
    log.Fatal(err)
}
defer sampler.Close()

adapter, err := meldotel.New(sampler, meldotel.Options{
    MeterProvider:          applicationMeterProvider,
    InstrumentationVersion: "0.1.0",
})
if err != nil {
    log.Fatal(err)
}
defer adapter.Close()

SchemaVersion and Instruments() expose the fixed contract. Instrument names start with meldbase. and have no attributes containing database paths, collection/index names, query text, document IDs, errors, actors or workspaces. Server instruments are simply not observed when the sampler has no server source. Values above the OTel API's signed int64 range saturate monotonically; Adapter.Stats() reports that condition.

Contract version 7 includes the aggregate meldbase.index.build.retention_lease.active and meldbase.index.build.retention.pressure gauges. They carry no dynamic attributes; the latter is set only when the build watermark is the binding Commit Log retention boundary, distinguishing normal online-build lag from a budget that needs operator attention.

Contract version 8 adds physical-generation and external rollback-anchor sequence/generation, lag, failure, timeout and synchronous-latency instruments. These remain fixed-cardinality engine aggregates and expose no database or anchor-service identity.

These are embedded-engine aggregates, so the adapter deliberately does not emit db.client.*. The OpenTelemetry database semantic conventions describe calls as observed by a database client, while this adapter observes the engine itself.

The package targets OpenTelemetry Go Metrics API v1.38, the newest stable release in the supported Go 1.23 toolchain line. Applications own SDK, reader, exporter, resource and collection interval choices.