After fbba5dae54e0396d859a7e32872d60e9909213a9, pingback was supposed to send a monthly heartbeat ping. Due to an implementation error, on DBMSs other than MySQL, the timestamp is not updated, so the rate of pings is only limited by the lock feature, producing one ping per hour assuming ObjectCache is configured appropriately.
A new installation ID is generated each time, because the insertion of the ID is rolled back when the query error occurs.
The effect on our statistics is shown in the graph below.
We should probably do a minor release, and also filter out all pings which have an MW version and DBMS known to be affected.