This is the base for Smart Router. Review and TODO comments are in the
code. This commit will be squashed several times so don't pay attention to this
specific commit message. I will add and remove TODO's in the code, rather
than save them in git commits. RBCommons will contain the history.
By iterating over the servers and sending the master's charset we are
guaranteed a "known good" charset. This also solves the problem where a
deactivated server reference would be used as the charset and server
version source.
If the execution of a session command fails on a master, it is retried
again. If the master is not available, the response will be returned from
one of the slaves.
The retrying of a read on a slave should only be done when the failing
server is waiting for a result and it was the last server from which a
result was expected.
If the master fails when a session command is being executed with
delayed_retry enabled, a null query would get placed into the query
queue. This change simply prevents the crash and closes the session even
though the query could be retried.
A query should not be queued if no responses are expected. The code that
executes queued queries should be dead code and this assertion would catch
it.
Older clients assume the plugin used for authentication is
mysql_native_password. If the client doesn't request plugin
authentication, don't treat it as an error.
The functionality is more a part of the provider than the context so it
should be defined in it. It also doesn't use any parts of the SSLContext
which makes it somewhat more clear that it doesn't belong there.
The monitor queries for logged in users with super-privileges and kicks them out to
prevent writes to master. Normal users can stay since their writes are prevented by
read_only. Also, the master-status is removed from the master manually to signal to
routers that no more writes should go to master.
If the authentication process fails due to an inability to start a
session, it should not be counted towards the number of failed
authentication attempts.
Plugins may send additional messages during authentication. These messages
often contain notifications such as password expiration dates. Both the client
and backend side authenticators now handle such messages. The messages are not
sent to the user, only the log. The requirement that only "Password: " is queried
still stands.
