Openmetrics label truncation

[Daniel Sabotta]

Hi Aki thanks for your reply,

I am using some dovecots behind a dovecot smtp proxy. Now I want to use OpenMetrics (with Pormetheus) to get metrics on 
which destination hosts the mails are delivered to. And my hostnames are longer than 32 characters.

I hope that explains my use case enough.


On 03.06.22 10:16 Aki Tuomi wrote:
>> On 03/06/2022 11:13 Daniel Sabotta <daniel.sabotta at securepoint.de> wrote:
>>
>>   
>> Hello,
>>
>> I'm using dovecot 2.3.18 and want to collect metrics with prometheus via openmetrics.
>>
>> I need to label the metrics with the destination host name.
>> The configuration works fine, but the label value is truncated after 32 chars (and a '...' is added).
>>
>> My config:
>>
>> service stats {
>>     inet_listener http {
>>       port = 9323
>>     }
>> }
>>
>> metric my_metric {
>>     filter = event=smtp_client_transaction_finished
>>     group_by = dest_host status_code
>> }
>>
>> I wrote a simple patch, that fixes that for me:
>>
>> diff --git a/src/stats/stats-metrics.c b/src/stats/stats-metrics.c
>> index 877c142546..30126563ff 100644
>> --- a/src/stats/stats-metrics.c
>> +++ b/src/stats/stats-metrics.c
>> @@ -357,7 +357,7 @@ stats_metric_sub_metric_alloc(struct metric *metric, const char *name, pool_t po
>>    	array_append_zero(&fields);
>>    	sub_metric = stats_metric_alloc(pool, metric->name, metric->set,
>>    					array_idx(&fields, 0));
>> -	sub_metric->sub_name = p_strdup(pool, str_sanitize_utf8(name, 32));
>> +	sub_metric->sub_name = p_strdup(pool, str_sanitize_utf8(name, 63));
>>    	array_append(&metric->sub_metrics, &sub_metric, 1);
>>    	return sub_metric;
>>    }
>>
>>
>> Why are labels truncated after 32?
>> Is there a reason I do not see?
>> I found no reasons in the openmetrics specification [1].
>>
>>
>> Thanks in advance
>>
>> Daniel
> 
> Can you epxlain us the usecase where you need such long labels?
> 
> Aki Tuomi