Increase metric name maximum length from 63 to 255 characters

[trask]

Addresses part of #3422

Changes

Increases metric name maximum length from 63 to 255 characters.

Rationale

This limitation has been problematic in the Java and .NET communities (at least) where longer metric names are not uncommon:

• OpenTelemetryMeterRegistry is registered despite instrumentation being disabled opentelemetry-java-instrumentation#6300
• Instrument name is invalid with Spring Security 6 opentelemetry-java-instrumentation#7448 (comment)
• Agent limits metric name length to 63 opentelemetry-java#5656
• [Instrumentation.EventCounters] Support long event source names better in EventCounters instrumentation opentelemetry-dotnet-contrib#740

As @aabmass mentions in #3422 (comment)

Looks like this [the 63 character limitation] was introduced in #1557 by @reyang

but I didn't see any rationale in that PR for why that number was chosen.

Is this a breaking change?

I don't think so, since it's a loosening (as opposed to strengthening) of the requirement, but you could also argue the alternative, since it's a "strengthening" of the requirement on telemetry consumers.

Alternatively, we could introduce a configurable setting for the metric name maximum length, but this would essentially add an (unbounded) strengthening of the requirement on telemetry consumers, so I'm not sure it's preferable.

[reyang]

Is this a breaking change?

I don't think so, since it's a loosening (as opposed to strengthening) of the requirement, but you could also argue the alternative, since it's a "strengthening" of the requirement on telemetry consumers.

Alternatively, we could introduce a configurable setting for the metric name maximum length, but this would essentially add an (unbounded) strengthening of the requirement on telemetry consumers, so I'm not sure it's preferable.

+1

[reyang]

I think this change is non-controversial (very small change, not breaking, doesn't require prototyping, sufficient demand), and can be included in 1.24.0 release? #3644 - FYI @carlosalberto

[joaopgrassi]

I did some looking on what most o11y vendors tell on their public pages about metric name/key size just as an FYI

• Dynatrace: 250 source
• Lightstep: 100 (I think?) source
• Datadog: 200 source
• New Relic: 255 (I think?) source

I think it should be fine since we are increasing the limit. If a back-end that accepted less than 255 truncated the metric name to fit their limit, would still continuing truncating as usual.

[reyang]

@trask would you update the changelog by moving the entry from 1.24.0 to unreleased?

[nayaniabhishek]

This is still not fixed for Java: https://github.com/open-telemetry/opentelemetry-java/blob/b3376a25d06bca773cfd16f600b660a0badf37a8/sdk/metrics/src/main/java/io/opentelemetry/sdk/metrics/SdkMeter.java#L49

[trask]

hi @nayaniabhishek, here's the Java PR: open-telemetry/opentelemetry-java#5697 (I'm also looking forward to this change)

but please note that it won't be merged until there has been a specification release that includes this spec change (see #2728 (comment))

[kalkibhagavanmeda]

Hi team
Any expectations like when will be releasing latest version of opentelemetry-api with increased metrics name length limitation

[trask]

hi @kalkibhagavanmeda, I'd suggest asking this in the language repository for the SDK you are using, e.g. this is implemented in the latest released Java SDK version (open-telemetry/opentelemetry-java#5697)