feature: prometheus histogram metrics

[sbilello]

Describe the Feature Request

Add Histogram metrics support https://prometheus.io/docs/practices/histograms/

Describe Preferred Solution

Annotation-based approach.

[berngp]

Hi @sbilello, we are using Micrometer as the mechanism to capture the metrics and they meters can be configured to export percentiles. Its a matter of just setting management.metrics.distribution.percentiles-histogram.gql=true.

[berngp]

@sbilello I think unless there is a specific feature that you suggest for the DGS framework, this looks more like a Q&A discussion.

[sbilello]

This is cool! Thanks, @berngp!
Yes, we can move this as Q&A but I was wondering if it would make sense to specify the percentiles as part of the configuration to reduce the number of buckets. See something like https://github.com/micrometer-metrics/micrometer/blob/main/micrometer-core/src/main/java/io/micrometer/core/annotation/Timed.java#L54

I was also wondering why we have different labels for the metrics:

gql_query_seconds_bucket{gql_queryComplexity="25",outcome="success",le="0.001",} 0.0
gql_resolver_seconds_bucket{gql_field="Query.getUserByUserIdInput",outcome="success",le="7.158278826",} 20.0

I will work on a custom tag as described in the doc unless we can not make consistent the tags between these 2 metrics.

I would like to show the duration in percentiles by query name for the gql_resolver* and the gql_query* metrics

[berngp]

Not sure I understand which labels are you referring to on gql.query vs gql.resolver.
The gql.query captures the entire scope of the GraphQL Query. Since each GraphQL Query can have multiple fields we can't capture them as part of the gql.query tag, I don't believe there is a way to express an array of values associated to a tag puls the cardinality will be problematic. The gql.resolver on the other hand can capture the GraphQL Field and therefore is able to include it.

[sbilello]

So a proposal would be to have 2 tags:

• tag for the query root name
• tag for hash of the payload
  It looks to be a hash prefix the one shown in their UI

Other question:
Is there any interest to limit the Percentiles collected in the histogram with some extra percentiles array?
https://github.com/micrometer-metrics/micrometer/blob/main/micrometer-core/src/main/java/io/micrometer/core/annotation/Timed.java#L54

[berngp]

I'm working on adding additional tags that will do what you mentioned. Regarding the percentiles, the idea was to have developers limit that via configuration instead of fixing it via de annotation.

[sbilello]

Thanks, @berngp. Configuration => Java Bean or Annotation or application.yml ?

[berngp]

We are talking about two different things.

1. The Percentiles in Micrometer. Configuring the percentiles in micrometer is better done via its supported configuration instead of having the annotation express that explicitly. Ref Micrometer's Adding percentiles, histograms, and SLA boundaries documentation

2. Adding a GQL Query identifier to the tags. This is a work in progress.

[sbilello]

Thanks for clarifying :)