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MariaDB MaxScale is a dynamic data routing platform that sits between a database layer and the clients of that database, the binlog router described here is somewhat different to that original concept, moving MariaDB MaxScale down to play a role within the database layer itself.
In a traditional MySQL replication setup a single master server is created and a set of slaves MySQL instances are configured to pull the binlog files from that master to the slaves.
There are some problems, however, in this setup; when the number of slaves grows an increasing load is placed on the master, to serve the binlogs to each slave.
When the master server fails, some action must be performed on every slave server before a new server can become the master server. Introducing a proxy layer between the master server and the slave servers can improve the situation, by reducing the load on the master to simply serving the proxy layer rather than all of the slaves. The slaves only need to be aware of the proxy layer and not of the real master server.
Removing need for the slaves to have knowledge of the master, greatly simplifies the process of replacing a failed master within a replication environment. The most obvious solution to the requirement for a proxy layer within a replication environment is to use a MariaDB or MySQL database instance. The database server is designed to allow this, since a slave server is able to be configured such that it will produce binary logs for updates it has itself received via replication from the master server.
In this case the server is known as an intermediate master, it is simultaneously a slave to the real master and a master to the other slaves in the configuration. Using an intermediate master does not, however, solve all the problems and introduces some new ones, due to the way replication is implemented. A slave server reads the binary log data and creates a relay log from that binary log. This log provides a source of SQL statements, which are executed within the slave in order to make the same changes to the databases on the slaves as were made on the master.
The above means that the data in the binary log of the intermediate master is not a direct copy of the data that was received from the binary log of the real master. The resultant changes to the database will be the same, provided no updates have been performed on the intermediate master that did not originate on the real master, but the steps to achieve those changes may be different.
In particular, if group commit functionality is used, to allow multiple transactions to commit in parallel, these may well be different on the intermediate master. This can cause a reduction in the parallelism of the commits and a subsequent reduction in the performance of the slave servers.
This re-execution of the SQL statements also adds latency to the intermediate master solution, since the full process of parsing, optimization and execution must occur for every statement that is replicated from the master to the slaves must be performed in the intermediate master. This latency introduces lag in the replication chain, with a greater delay being introduced from the time a transaction is committed on the master until the data is available on the slaves.
Use of an intermediate master does improve the process of failover of the master server, since the slaves are only aware of the intermediate master the process of promoting one of the existing slaves to become the new master only involves that slave and the intermediate master.
A slave can become the new master as soon as all the changes from the intermediate master have been processed. The intermediate master then needs to be reset to the correct point in the binary log of the new master and replication can continue. An added complexity that needs to be dealt with is the failure of the intermediate master itself.
If this occurs then the same problem as described earlier exists, all slaves must be updated when a new intermediate master is created. If multiple intermediate masters are used, there is also a restriction that slaves can not be moved from the failed intermediate master to another intermediate master due to the fact that the binlog on the different intermediate nodes are not guaranteed to be the same.
It acts as a slave to the real master and as a master to the slaves, in the same way as an intermediate master does. However, it does not implement any re-execution of the statements within the binary log. MariaDB MaxScale creates a local cache of the binary logs it receives from the master and will serve binary log events to the slaves from this cache of the master's binary log. This means that the slaves will always get binary log events that have a one-to-one correlation to those written by the master.
Parallelism in the binary log events of the master is maintained in the events that are observed by the slaves. In the MariaDB MaxScale approach, the latency that is introduced is mostly the added network latency associated with adding the extra network hop.
There is no appreciable processing performed at the MariaDB MaxScale level, other than for managing the local cache of the binlog files. In addition, every MariaDB MaxScale that is acting as a proxy of the master will have exactly the same binlog events as the master itself.
This means that a slave can be moved between any of the MariaDB MaxScale server or to the real master without a need to perform any special processing. The result is much simpler behavior for failure recovery and the ability to have a very simple, redundant proxy layer with slaves free to both between the proxies. In this case the master server should be considered as the database backend and the slave servers as the clients of MariaDB MaxScale.
As with any MariaDB MaxScale configuration a good starting point is with the service definition with the maxscale. The service requires a name which is the section name in the ini file, a type parameter with a value of service and the name of the router plugin that should be loaded. In the case of replication proxies this router name is binlogrouter.
Other standard service parameters need to be given in the configuration section that are used to retrieve the set of users from the backend master database, also a version string can be given such that the MariaDB MaxScale instance will report this version string to the slave servers that connect to MariaDB MaxScale.
The user and passwd entries in the above example are used in order for MariaDB MaxScale to populate the credential information that is required to allow the slaves to connect to MariaDB MaxScale. The master server details are currently provided by a master. The final configuration requirement is the router specific options.
In the binlog dir there is also the 'cache' directory that contains data retrieved from the master during registration phase and the master.
This is used to set the unique uuid that the binlog router uses when it connects to the master server. If no explicit value is given for the uuid in the configuration file then a uuid will be generated.
As with uuid, MariaDB MaxScale must have a unique server-id for the connection it makes to the master, this parameter provides the value of server-id that MariaDB MaxScale will use when connecting to the master. This may either be the same as the server-id of the real master or can be chosen to be different if the slaves need to be aware of the proxy layer. The real master server-id will be used if the option is not set.
It is a requirement of replication that each slave have a unique UUID value. The MariaDB MaxScale router will identify itself to the slaves using the uuid of the real master if this option is not set.
The MariaDB MaxScale router will identify itself to the slaves using the server version of the real master if this option is not set. The MariaDB MaxScale router will identify itself to the slaves using the server hostname of the real master if this option is not set. This user name must have the rights required for replication as with any other user that a slave uses for replication purposes.
If the user parameter is not given in the router options then the same user as is used to retrieve the credential information will be used for the replication connection, i. This user is also the only one available for Binlog Server administration when the connection with master is not ready yet: The password of the above user. If the password is not explicitly given then the password in the service entry will be used. This defines the value of the heartbeat interval in seconds for the connection to the master.
MariaDB MaxScale requests the master to ensure that a binlog event is sent at least every heartbeat period. If there are no real binlog events to send the master will sent a special heartbeat event. The default value for the heartbeat period is every 5 minutes. The current interval value is reported in the diagnostic output.
This defines whether on off MariaDB MaxScale sends to the slave the heartbeat packet when there are no real binlog events to send. The default value if 'off', no heartbeat event is sent to slave server. If value is 'on' the interval value requested by the slave during registration is reported in the diagnostic output and the packet is send after the time interval without any event to send. This parameter is used to define the maximum amount of data that will be sent to a slave by MariaDB MaxScale when that slave is lagging behind the master.
In this situation the slave is said to be in "catchup mode", this parameter is designed to both prevent flooding of that slave and also to prevent threads within MariaDB MaxScale spending disproportionate amounts of time with slaves that are lagging behind the master.
The default value of burstsize is 1Mb and will be used if burstsize is not given in the router options. When MariaDB MaxScale starts an error message may appear if current binlog file is corrupted or an incomplete transaction is found. This parameter controls whether binlog server could ask Master server to start the Semi-Synchronous replication. This parameter sets the maximum length of the certificate authority chain that will be accepted. Legal values are positive integers.
This applies to SSL connection to master server that could be acivated either by writing options in master. This parameter cannot be modified at runtime, default is 9. Additional informatons about Binlog files encryption can be found here: The minimum set of router options that must be given in the configuration are are server-id and master-id , default values may be used for all other options. As per any service in MariaDB MaxScale a listener section is required to define the address, port and protocol that is used to listen for incoming connections.
The binlog router module of MariaDB MaxScale produces diagnostic output that can be viewed via the maxadmin client application. Running the maxadmin command and issuing a show service command will produce a considerable amount of output that will show both the master connection status and statistics and also a block for each of the slaves currently connected.
In order to use it with MySQL 5. Connected or new slave connections are not affected: When router is configured and it is properly working it is possible to change the master parameters. First step is stop the replication from the master.
Further details about level of encryption or certificates could be found here Configuration Guuide. If there is a master server maintenance and a slave is being promoted as master it should be checked that binlog file and position are valid: This command removes master. MariaDB MaxScale as a Binlog Server MariaDB MaxScale is a dynamic data routing platform that sits between a database layer and the clients of that database, the binlog router described here is somewhat different to that original concept, moving MariaDB MaxScale down to play a role within the database layer itself.
Service Configuration As with any MariaDB MaxScale configuration a good starting point is with the service definition with the maxscale. In the current implementation of the router only a single server can be used. Please note that semi-sync replication is only related to binlog server to Master communication.
A complete example of a service entry for a binlog router service would be as follows. Listener Section As per any service in MariaDB MaxScale a listener section is required to define the address, port and protocol that is used to listen for incoming connections.
Started Master connection DCB: Binlog Dump Binlog directory: Thu Jan 29 Disabled Backend databases Change the Master server configuration When router is configured and it is properly working it is possible to change the master parameters. A successful configuration change results in master.