I am so confused about _sum part of histogram metric.
Please explain me how to read and understand following metrics (all unrelated labels are same and omitted for briefness):
prometheus_http_response_size_bytes_bucket
prometheus_http_response_size_bytes_bucket{le="+Inf"} 1
prometheus_http_response_size_bytes_bucket{le="100"} 1
prometheus_http_response_size_bytes_bucket{le="1000"} 1
prometheus_http_response_size_bytes_bucket{le="10000"} 1
prometheus_http_response_size_bytes_bucket{le="100000"} 1
prometheus_http_response_size_bytes_bucket{le="1e+06"} 1
prometheus_http_response_size_bytes_bucket{le="1e+07"} 1
prometheus_http_response_size_bytes_bucket{le="1e+08"} 1
prometheus_http_response_size_bytes_bucket{le="1e+09"} 1
prometheus_http_response_size_bytes_sum
prometheus_http_response_size_bytes_sum 29
Shouldn't prometheus_resposnse_size_bytes_sum, be the sum of prometheus_reponse_size_bytes_bucket? If it is yes, as you see there are only nine with the result of 1. So what about value 29?