etcd_debugging_mvcc_db_total_size_in_bytes metric freeze

[mwf]

Hi guys, maybe it's already fixed, but I decided to ask anyway.

etcd server version 3.1.5

I've run a compaction + defrag on cluster and found out that etcd_debugging_mvcc_db_total_size_in_bytes metrics is "frozen" somehow.

It returns old DB size, before the defrag.
It returns the real size only after etcdctl endpoint status is called for the particular node.

curl http://<host>:4001/metrics | grep db_total 
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:--  0:00:01 --:--:--     0# HELP etcd_debugging_mvcc_db_total_size_in_bytes Total size of the underlying database in bytes.
# TYPE etcd_debugging_mvcc_db_total_size_in_bytes gauge
etcd_debugging_mvcc_db_total_size_in_bytes 2.19680768e+09

ETCDCTL_API=3 etcdctl -w=table endpoint status
+----------------+------------------+---------+---------+-----------+-----------+------------+
|    ENDPOINT    |        ID        | VERSION | DB SIZE | IS LEADER | RAFT TERM | RAFT INDEX |
+----------------+------------------+---------+---------+-----------+-----------+------------+
| 127.0.0.1:2379 | e273c0dc9c7d588b | 3.1.5   | 807 kB  | false     |      1999 | 2023933200 |
+----------------+------------------+---------+---------+-----------+-----------+------------+

curl http://<host>:4001/metrics | grep db_total 
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
 58 41876   58 24248    0     0  32760      0  0:00:01 --:--:--  0:00:01 32723# HELP etcd_debugging_mvcc_db_total_size_in_bytes Total size of the underlying database in bytes.
# TYPE etcd_debugging_mvcc_db_total_size_in_bytes gauge
etcd_debugging_mvcc_db_total_size_in_bytes 806912

Is it fixed already?

[mwf]

On some of our clusters it got "unfrozen" by itself after ~20 minutes.
On some - it showed old data for 40+ minutes and only manual endpoint status call fixed the metrics data.

So the bug may not be easy to reproduce. But we found the time-lag on every cluster we have.