Add support for custom attributes function

[urdarinda]

Sometimes we want to add custom attributes to metrics in order to give better context with the application.

Example,
I want to identify which API is responsible for calling this redis command and group by the calling API

[urdarinda]

@ofekshenawa Please take a look at this one

[ofekshenawa]

Can you please add some tests?

[urdarinda]

Can you please add some tests?

Added tests for metrics and custom attributes

[urdarinda]

@ofekshenawa Added tests but something weird is happening with the tests. It was passing tests yesterday and failing now. It should only fail on 1.19 afaik because the metric sdk version I am using requires 1.20 and above ( not able to find a working version before that)

[urdarinda]

@ofekshenawa Fixed the tests, but it is failing on 1.19 ( the test setup for metrics require 1.20+) , before those not able to find test functions for metric testing. How can we proceed?

[urdarinda]

@ndyakov can you please take a look at this one?

Thanks

[ndyakov]

@urdarinda I do not have a lot of context on the redisotel, but don't see a breaking change. Would you mind updating the example in the examples as well?

[urdarinda]

@ndyakov added

[ndyakov]

@urdarinda please resolve conflicts and request a review from @monkey92t since maybe he has more background with the otel package than me.

[urdarinda]

@monkey92t please review

[monkey92t]

1、In the example, the demonstration is for tracing, but the actual implementation only includes metrics. Would you like to add tracing?

2、Based on the example and the code, the custom attributes seem to be global and cannot be changed based on execution commands or any conditions. In the go-redis hook, the ctx does not contain much useful information, making it difficult to modify custom variables through ctx.

3、

attrs := make([]attribute.KeyValue, 0, len(mh.attrs)+2)
attrs = append(attrs, mh.attrsFunc(ctx)...)
attrs = append(attrs, mh.attrs...)
attrs = append(attrs, attribute.String("type", "command"))
attrs = append(attrs, statusAttr(err))

This is a Go-related issue. Obviously, a slice expansion will occur here, and we should avoid it.

[urdarinda]

@monkey92t

1、In the example, the demonstration is for tracing, but the actual implementation only includes metrics. Would you like to add tracing?

Added for tracing, updated test as well

2、Based on the example and the code, the custom attributes seem to be global and cannot be changed based on execution commands or any conditions. In the go-redis hook, the ctx does not contain much useful information, making it difficult to modify custom variables through ctx.

This can be actually to augment the metrics/traces when used with other frameworks. I can add things like rpc.method etc to attribute the calling API to redis calls and create dashboards on top of that. Updated the example demonstrating that ( very crude)

3、

attrs := make([]attribute.KeyValue, 0, len(mh.attrs)+2)
attrs = append(attrs, mh.attrsFunc(ctx)...)
attrs = append(attrs, mh.attrs...)
attrs = append(attrs, attribute.String("type", "command"))
attrs = append(attrs, statusAttr(err))

This is a Go-related issue. Obviously, a slice expansion will occur here, and we should avoid it.

How do you suggest we do it? I believe this is the only way to expand a slice into individual values for now

[monkey92t]

For custom parameters, should we customize the parameters based on the form of a command or a key?

Regarding the Go slice issue, we should first calculate the length of the slice and then allocate memory. In the PR, only elements were appended to the slice without recalculating the slice length and allocating memory.