Due to the fact that both client connections and listeners use sessions in
2.3, the client_count tracking must be done inside the client DCB. In
addition to this, the max_connections check didn't take the current
pending connection into account which caused an off-by-one error.
This commit fixes the connection_limit test failure that was introduced by
commit 6306519e5e75575ba083ee2f0edfe7e624da5d26.
By incrementing the counters when the session is created, we know that the
counter will always be decremented correctly. This does cause the listener
session to be counted as an actual session but this is already present in
the statistics calculations and is something we have to live with in 2.3
This change also makes it possible to overshoot the connection count
limitation as the session creation is delayed until authentication
fails. Both of these problems are fixed in 2.4.
The FakeEventTask called the actual DCB handler with a fake task but it
didn't set the fake event flag. This caused KILL queries to be treated as
if they were network errors.
The hangup and error handlers now have unique messages. Although the
behavior in the handlers is practically the same in both cases, the cause
of the error is not the same.
If a socket error is present, it is added to the error message. If an
error is present, it should clearly show the reason why the TCP socket was
closed.
The is_fake_event boolean helps distinguish fake events from real
ones. This makes figuring out the real source of hangup events easier.
When fake hangup events are delivered via DCBs, the current DCB would not
be updated. This would cause error messages without a session ID which
makes failure analysis harder.
SSLContext is now used everywhere except the binlogrouter which still
allocates the contexts itself. Fixing the binlogrouter's misuse of
internal structures is a rather large undertaking and for this reason the
SSLContext will be taken into use there in a separate commit.
The code that selects which worker to assign the DCB to is now completely
in the Listener class. This removes the need to change the ownership of a
DCB after it has been allocated.
Given the assumption that queries are rarely 16MB long and that
realistically the only time that happens is during a large dump of data,
we can limit the size of a single read to at most one MariaDB/MySQL packet
at a time. This change allows the network throttling to engage a lot
sooner and reduces the maximum overshoot of throtting to 16MB.
The function allocated a constant-sized chunk of memory for all messages
which was excessive as well as potentially dangerous when used with large
strings.
If a DCB was closed and a hangup event was sent to it via
dcb_hangup_foreach shortly after it was closed, the DCB would still
receive it even if it was closed. To prevent this, events must only be
delivered to DCBs if they haven't been closed.
