# MariaDB MaxScale 2.4.0 Release Notes

Release 2.4.0 is a Beta release.

This document describes the changes in release 2.4.0, when compared to
release 2.3.

For any problems you encounter, please consider submitting a bug
report at [Jira](https://jira.mariadb.org).

## Changed Features

### Section and object names

Section and object names starting with `@@` are now reserved for
use by MaxScale itself. If any such names are encountered in
configuration files, then MaxScale will not start.

Whitespace in section names that was deprecated in 2.2 will now be
rejected and cause the startup of MaxScale to fail.

### Binding on network ports

MaxScale 2.4.0 will now use the SO_REUSEPORT capability offered by newer kernels
that allows reuse of network listener ports. In practice this means improved
connection creation speed with more dynamic balancing of connections.

As a side-effect of this, it is possible for two MaxScale instances to bind on
the same listener port on systems that have Linux kernels newer than 3.9. This
can only happen if the MaxScale instances use completely different directory
structures (i.e. different `--basedir` arguments). Normal use of MaxScale still
detects multiple MaxScales trying to bind to the same ports. Almost always, this
will not have any negative side-effects.

### Maintenance mode and Readwritesplit

Readwritesplit now allows open transactions to finish if the master is put into
maintenance mode. To forcefully close all connections to a server use the
`maxctrl set server <name> maintenance --force` command.

### Stronger hashing algorithm for admin user passwords

The administrative user passwords are now stored as SHA2-512 hashes which is an
improvement over the older MD5 hashing algorithm. New users will use the
stronger algorithm but old users will continue using the weaker one. To upgrade
administrative users, recreate the user.

## Dropped Features

### `debugcli` and `telnetd`

The `debugcli` router and the `telnetd` protocol module it uses have been
removed.

### `ndbclustermon`

The `ndbclustermon` module has been removed.

### `mmmon`

The `mmmon` module has been removed as the `mariadbmon` monitor largely does
what it used to do.

## New Features

### Servers can be drained

It is now possible to drain a server, which means that existing
connections to the server can continue to be used but new connections
are no longer created to the server.

In the output of `maxctrl`, the fact that a server is being drained
is visible in the `State` column as the value `Draining`.
```
┌─────────┬─────────────────┬──────┬─────────────┬───────────────────────────────┬───────┐
│ Server  │ Address         │ Port │ Connections │ State                         │ GTID  │
├─────────┼─────────────────┼──────┼─────────────┼───────────────────────────────┼───────┤
│ Server1 │ 192.168.121.159 │ 3306 │ 2           │ Master, Running               │ 0-1-6 │
├─────────┼─────────────────┼──────┼─────────────┼───────────────────────────────┼───────┤
│ Server2 │ 192.168.121.80  │ 3306 │ 1           │ Draining, Slave, Running      │ 0-1-6 │
├─────────┼─────────────────┼──────┼─────────────┼───────────────────────────────┼───────┤
│ Server3 │ 192.168.121.122 │ 3306 │ 2           │ Slave, Running                │ 0-1-6 │
├─────────┼─────────────────┼──────┼─────────────┼───────────────────────────────┼───────┤
│ Server4 │ 192.168.121.144 │ 3306 │ 2           │ Slave, Running                │ 0-1-6 │
└─────────┴─────────────────┴──────┴─────────────┴───────────────────────────────┴───────┘
```
A server is set in the _Draining_ state the same way as it is
set in the _Maintenance_ state:
```
$ maxctrl set server Server2 drain
```
Note that although the state is displayed as `Draining`, when setting
and clearing the state, the word `drain` is used.

Note that the full implication of draining a server depends upon
both on the role of the server and on the router being used, and its
configuration.

For instance, if readwritesplit is used and the server being drained
is a slave, then from a client's perspective there will be no difference;
readwritesplit will simply not use that server. However, if the server
being drained is the master, then it will not be possible to connect
unless `master_failure_mode` has been set to something else but the
default `fail_instantly`.

Once the server has been drained, the state will be `Drained`.

### Cluster

The servers a service uses can now be specified using the `cluster`
parameter of the service.
```
[TheService]
...
cluster=TheMonitor
```
In this case, the servers of the service will be defined by the
referred to monitor. Note that the parameters `servers` and `cluster`
are mutually exclusive.

### Durations

In the MaxScale configuration file, durations can now be suffixed with
`h`, `m`, `s` or `ms` to indicate that the duration is specified as
hours, minutes, seconds or milliseconds.

Please see the
[configuration guide](../Getting-Started/Configuration-Guide.md#durations)
for details.

_Not_ providing an explicit unit has been deprecated in MaxScale 2.4.

### Query Classifier Cache

It is now possible to examine the contents of the query classifier cache.
The REST-API endpoint is
```
/v1/maxscale/query_classifier/cache
```
and the equivalent _maxctrl_ command
```
maxctrl show qc_cache
```
The output shows the statements (the canonical version) in the cache,
the number of times they have been encountered and how they have been
classified.

### REST API & MaxCtrl: Hard maintenance mode

The new `--force` option for the `set server` command in MaxCtrl allows all
connections to the server in question to be closed when it is set into
maintenance mode. This causes idle connections to be closed immediately.

For more information, read the
[REST-API](../REST-API/Resources-Server.md#set-server-state) documentation for
the `set` endpoint.

## Bug fixes

[Here is a list of bugs fixed in MaxScale 2.4.0.](https://jira.mariadb.org/issues/?jql=project%20%3D%20MXS%20AND%20issuetype%20%3D%20Bug%20AND%20status%20%3D%20Closed%20AND%20fixVersion%20%3D%202.4.0)

## Known Issues and Limitations

There are some limitations and known issues within this version of MaxScale.
For more information, please refer to the [Limitations](../About/Limitations.md) document.

## Packaging

RPM and Debian packages are provided for the Linux distributions supported
by MariaDB Enterprise.

Packages can be downloaded [here](https://mariadb.com/resources/downloads).

## Source Code

The source code of MaxScale is tagged at GitHub with a tag, which is identical
with the version of MaxScale. For instance, the tag of version X.Y.Z of MaxScale
is X.Y.Z. Further, *master* always refers to the latest released non-beta version.

The source code is available [here](https://github.com/mariadb-corporation/MaxScale).
