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Maintenance Mode

Basic Concepts​

When in maintenance mode, Kylin nodes will not be able to modify metadata, and only read operations such as queries will not be affected

Entering maintenance mode​

Run the following command to enter maintenance mode:

${KYLIN_HOME}/bin/kylin.sh org.apache.kylin.tool.MaintainModeTool -on -reason ${reason}

Note:

  • You need to use the argument -reason to explain why you turn on maintenance mode。

    • When it is in maintenance mode, it is not allowed to enter maintenance mode again. You need to manually exit maintenance mode first

  • ${reason} refers to the reason for entering maintenance mode. There are no fixed characters. You can enter any word, such as upgrade

    When in maintenance mode, you will get following prompt:

    maintenance mode

    metadata modification operations, such as create project, load/unload tables, create/update models, etc., can't be executed.

    If you do the above, the following errors will occur:

    forbidden modify metadata promoting during maintenance mode

    forbidden modify metadata during maintenance mode

Exiting Maintenance mode​

Run the following command to exit maintenance mode:

${KYLIN_HOME}/bin/kylin.sh org.apache.kylin.tool.MaintainModeTool -off

Note：While system is already in maintenance mode, the system will prompt you after executing command. In speciality, you can use -f or --force parameter to force to turn off maintenance mode, to release all occupation of project.

After the command was executed, you may not modify metadata immediately. It should be waiting Kylin nodes to get the resources. You can refer following properties: 

kylin.server.leader-race.heart-beat-interval=30

Its unit is seconds. You should wait up to 30 seconds.

During the maintenance, if you try to modify metadata, you will get following prompt:

system recover from maintenance mode

Recommendations for the use of maintenance mode​

Maintenance mode is provided to prevent metadata write conflicts in the system. In principle, users are not recommended to turn on or turn off this function manually. When running the following commands, the system will automatically turn on the maintenance mode, and turn off the maintenance mode after the operation ends.