The TL;DR for the change is that we allow QueryRouter to set the active shard to None. This signals to the Pool::get method that we have no shard selected. The get method follows a no_shard_specified_behavior config to know how to route the query.
Original PR description
Ruby-pg library makes a startup query to SET client_encoding to ... if Encoding.default_internal value is set (Code). This query is troublesome because we cannot possibly attach a routing comment to it. PgCat, by default, will route that query to the default shard.
Everything is fine until shard 0 has issues, Clients will all be attempting to send this query to shard0 which increases the connection latency significantly for all clients, even those not interested in shard0
This PR introduces no_shard_specified_behavior that defines the behavior in case we have routing-by-comment enabled but we get a query without a comment. The allowed behaviors are
random: Picks a shard at random
random_healthy: Picks a shard at random favoring shards with the least number of recent connection/checkout errors
shard_<number>: e.g. shard_0, shard_4, etc. picks a specific shard, everytime
In order to achieve this, this PR introduces an error_count on the Address Object that tracks the number of errors since the last checkout and uses that metric to sort shards by error count before making a routing decision.
I didn't want to use address stats to avoid introducing a routing dependency on internal stats (We might do that in the future but I prefer to avoid this for the time being.
I also made changes to the test environment to replace Ruby's TOML reader library, It appears to be abandoned and does not support mixed arrays (which we use in the config toml), and it also does not play nicely with single-quoted regular expressions. I opted for using yj which is a CLI tool that can convert from toml to JSON and back. So I refactor the tests to use that library.
* Add a new exec_simple_query method
This adds a new `exec_simple_query` method so we can make 'out of band'
queries to servers that don't interfere with pools at all.
In order to reuse startup code for making these simple queries,
we need to set the stats (`Reporter`) optional, so using these
simple queries wont interfere with stats.
* Add auth passthough (auth_query)
Adds a feature that allows setting auth passthrough for md5 auth.
It adds 3 new (general and pool) config parameters:
- `auth_query`: An string containing a query that will be executed on boot
to obtain the hash of a given user. This query have to use a placeholder `$1`,
so pgcat can replace it with the user its trying to fetch the hash from.
- `auth_query_user`: The user to use for connecting to the server and executing the
auth_query.
- `auth_query_password`: The password to use for connecting to the server and executing the
auth_query.
The configuration can be done either on the general config (so pools share them) or in a per-pool basis.
The behavior is, at boot time, when validating server connections, a hash is fetched per server
and stored in the pool. When new server connections are created, and no cleartext password is specified,
the obtained hash is used for creating them, if the hash could not be obtained for whatever reason, it retries
it.
When client authentication is tried, it uses cleartext passwords if specified, it not, it checks whether
we have query_auth set up, if so, it tries to use the obtained hash for making client auth. If there is no
hash (we could not obtain one when validating the connection), a new fetch is tried.
Once we have a hash, we authenticate using it against whathever the client has sent us, if there is a failure
we refetch the hash and retry auth (so password changes can be done).
The idea with this 'retrial' mechanism is to make it fault tolerant, so if for whatever reason hash could not be
obtained during connection validation, or the password has change, we can still connect later.
* Add documentation for Auth passthrough
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
