Better usability for mongodb_collstats_storageStats_indexSizes_.* metrics #882
Description
#97 introduce index sizes metrics years ago, which is useful for huge indexes monitoring.
However, similar to no.3 in #97 (comment), for every index, there will be a separate metric for every single index. For example, mongodb_collstats_storageStats_indexSizes_user_id_1 and mongodb_collstats_storageStats_indexSizes_id_1 could be the same metric (index size) for a same collection.
The number of indexes, or to be more precisely, the number of series is not a major concern from our side.
The problem is it's not of good usability. Here's the argue:
To query the index sizes, we have to perform a regex __name__ query, like {__name__=~"mongodb_collstats_storageStats_indexSizes_.*"}. This works but IMO is against the normal usage pattern of prometheus. A quote from their best practice:
should represent the same logical thing-being-measured across all label dimensions.
Therefor I propose we change the metric format from mongodb_collstats_storageStats_indexSizes_keya_1_keyb_1 to mongodb_collstats_storageStats_indexSizes{name="keya_1_keyb_1"}.The name of index will be a label instead of being included in the metric name.Since it's a backward break change, there should be a flag control this incompatible change. I'm ok with it being default old format.
Any thoughts?