feat: add metrics with msg size histogram

[alrevuelta]

closes #1626

• Add a new metric waku_histogram_message_size containing the message size histogram.
• This allows to have better observability on the message distribution size.

Suggested usage:

• 98% of the messages are between 5 and 15 kBytes
• 0.7% of the messages are between 50 and 100 kBytes.
• 99% of the messages are lower than 37.6 kBytes.

[jm-clius]

LGTM

[jm-clius]

Perhaps I'm missing something about how nim-metrics work, but should the Inf bucket be declared?

[alrevuelta]

Indeed, added in e27702c to be explicit.

But looks like its automatically added. Have seen examples that both provide Inf and not, but seems that even without it its automatically added. Example without having Inf in bucket.

$ curl localhost:8004/metrics | grep histogram
...
waku_histogram_message_size_sum 0.0
waku_histogram_message_size_count 0.0
waku_histogram_message_size_created 1681987077.0
waku_histogram_message_size_bucket{le="0.0"} 0.0
waku_histogram_message_size_bucket{le="5.0"} 0.0
waku_histogram_message_size_bucket{le="15.0"} 0.0
waku_histogram_message_size_bucket{le="50.0"} 0.0
waku_histogram_message_size_bucket{le="100.0"} 0.0
waku_histogram_message_size_bucket{le="300.0"} 0.0
waku_histogram_message_size_bucket{le="700.0"} 0.0
waku_histogram_message_size_bucket{le="1000.0"} 0.0
waku_histogram_message_size_bucket{le="+Inf"} 0.0   <---

[jm-clius]

Thanks! I thought it may be added automatically, but wasn't sure.

[vpavlin]

Awesome! LGTM