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  1. MariaDB Server
  2. MDEV-14533

Provide information_schema tables using which hardware information can be obtained.

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    • Sprint:
      10.1.32

      Description

      MaxScale should be able to react when some node of a cluster hits a disk-full situation.

      For instance, if the master in a master-slave cluster hits a disk-full situation, MaxScale should promote some existing slave to master and remove the old master from the cluster. That way, a client connected to MaxScale would not necessarily detect anything special at all.

      In order to do that, MaxScale must be able to detect that a disk-full situation has occurred. It's difficult and unreliable to do that using MariaDB itself, for instance, by trying to create a table and assuming it was a disk-full situation in case the creation fails or the attempt ends with a timeout. Further, that approach would not allow MaxScale to become aware of the situation before the disk actually becomes full.

      A more reliable way would be to actually monitor the disk-space situation on the node and use that for the decision making, but arranging that is rather complex and fragile.

      A robust solution would be if there were a pseudo table or pseudo tables in information_schema using which information about the node could be found out. For instance as follows:

      MariaDB [information_schema]> select * from information_schema.system;
      +------+--------+-----+
      | CPUS | MEMORY | ... |
      +---------------------+
      | 4    | 4096   | ... |
      +---------------------+
      1 row in set (0.00 sec)
       
      MariaDB [information_schema]> select * from information_schema.disks;
      +------------+------------+----------+-----+
      | Filesystem |  1K-blocks |     Used | ... |
      +------------+------------+----------+-----+
      | udev       |    8156512 |        0 |     |
      | tmpfs      |    1635388 |     9820 | ... |
      | /dev/sda3  |   47929956 | 28150612 |     |
      | ...        |        ... |      ... |     |
      +------------+------------+----------+-----+
      10 rows in set (0.00 sec)
      

      With this information available, MaxScale could automatically take corrective action in case the amount of used disk-space grows above, say, 90%.

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              • Assignee:
                holyfoot Alexey Botchkov
                Reporter:
                johan.wikman Johan Wikman
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                • Created:
                  Updated:
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