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MXS-2168 Add documentation on "assume_unique_hostnames"

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Esa Korhonen 2018-11-16 18:10:48 +02:00
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commit c61aaee0ba
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Documentation/Monitors/MariaDB-Monitor.md
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@ -8,6 +8,7 @@ Table of Contents
* [Configuration](#configuration)
* [Common Monitor Parameters](#common-monitor-parameters)
* [MariaDB Monitor optional parameters](#mariadb-monitor-optional-parameters)
* [assume_unique_hostnames](#assume_unique_hostnames)
* [detect_replication_lag](#detect_replication_lag)
* [detect_stale_master](#detect_stale_master)
* [detect_stale_slave](#detect_stale_slave)
@ -137,6 +138,33 @@ These are optional parameters specific to the MariaDB Monitor. Failover,
switchover and rejoin-specific parameters are listed in their own
[section](#cluster-manipulation-operations).
### `assume_unique_hostnames`
Boolean, default: ON. When active, the monitor assumes that server hostnames and
ports are consistent between the MaxScale configuration file server definitions
and the "SHOW ALL SLAVES STATUS" outputs of the servers. Specifically, the
monitor assumes that if server A is replicating from server B, then A must have
a slave connection with `Master_Host` and `Master_Port` equal to B's address and
port in the configuration file. If this is not the case, e.g. an IP is used in
the server while a hostname is given in the file, the monitor will misinterpret
the topology.
This setting must be ON to use any cluster operation features such as failover
or switchover, because MaxScale uses the addresses and ports in the
configuration file when issuing "CHANGE MASTER TO"-commands.
If the network configuration is such that the addresses MaxScale uses to connect
to backends are different from the ones the servers use to connect to each
other, `assume_unique_hostnames` should be set to OFF. In this mode, MaxScale
uses server id:s it queries from the servers and the `Master_Server_Id` fields
of the slave connections to deduce which server is replicating from which. This
is not perfect though, since MaxScale doesn't know the id:s of servers it has
never connected to (e.g. server has been down since MaxScale was started). Also,
the `Master_Server_Id`-field may have an incorrect value if the slave connection
has not been established. MaxScale will only trust the value if the monitor has
seen the slave connection IO thread connected at least once. If this is not the
case, the slave connection is ignored.
### `detect_replication_lag`
Deprecated and unused as of MaxScale 2.3. Can be defined but is ignored.