This is an implementation of Query mirroring in PgCat (outlined here #302)
In configs, we match mirror hosts with the servers handling the traffic. A mirror host will receive the same protocol messages as the main server it was matched with.
This is done by creating an async task for each mirror server, it communicates with the main server through two channels, one for the protocol messages and one for the exit signal. The mirror server sends the protocol packets to the underlying PostgreSQL server. We receive from the underlying PostgreSQL server as soon as the data is available and we immediately discard it. We use bb8 to manage the life cycle of the connection, not for pooling since each mirror server handler is more or less single-threaded.
We don't have any connection pooling in the mirrors. Matching each mirror connection to an actual server connection guarantees that we will not have more connections to any of the mirrors than the parent pool would allow.
Connection to the CI databases is viewed by Postgres as coming from localhost. The pg_hba.conf file generated by the docker image uses trust for these connections, that's why we had no test coverage on SASL and md5 branches.
This PR fixes this issue. There was also an issue with under-reporting code coverage. This should be fixed now
We have encountered a case where PgCat pools were stuck following a database incident. Our best understanding at this point is that the PgCat -> Postgres connections died silently and because Tokio defaults to disabling keepalives, connections in the pool were marked as busy forever. Only when we deployed PgCat did we see recovery.
This PR introduces tcp_keepalives to PgCat. This sets the defaults to be
keepalives_idle: 5 # seconds
keepalives_interval: 5 # seconds
keepalives_count: 5 # a count
These settings can detect the death of an idle connection within 30 seconds of its death. Please note that the connection can remain idle forever (from an application perspective) as long as the keepalive packets are flowing so disconnection will only occur if the other end is not acknowledging keepalive packets (keepalive packet acks are handled by the OS, the application does not need to do anything). I plan to add tcp_user_timeout in a follow-up PR.
* create a hyper server and add option to enable it in config
* move prometheus stuff to its own file; update format
* create metric type and help lookup table
* finish the metric help type map
* switch to a boolean and a standard port
* dont emit unimplemented metrics
* fail if curl returns a non 200
* resolve conflicts
* move log out of config.show and into main
* terminating new line
* upgrade curl
* include unimplemented stats
