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Unable to fetch information about flushing


I am new to PMM and I am trying to troubleshoot my database redo log usage, checkpoint age and InnoDB flushing.

I have installed PMM Server 2 in a docker container and connected it to a remote MySQL server, running MariaDB 10.5 on another container, where I created the required user with the permissions as per documentation states.

Most of MySQL metrics are fetched without issues, however for the ones relating to flushing, I only get "No data", as on the following screenshot:

I am not an expert with PMM but tried to explore that chart and see it uses "mysql_info_schema_innodb_metrics_buffer_buffer_flush_adaptive_total_pages". By the name I suppose it should be getting data from information_schema.INNODB_METRICS, by name "buffer_flush_adaptive_total_pages", which I can fetch from my DB:

[code]MariaDB [information_schema]> select * from innodb_metrics WHERE name='buffer_flush_sync_total_pages' \G;

*************************** 1. row ***************************

      NAME: buffer_flush_sync_total_pages

   SUBSYSTEM: buffer

     COUNT: 1763445

   MAX_COUNT: 1763445


   AVG_COUNT: 2988

  COUNT_RESET: 1763445




  TIME_ENABLED: 2020-09-02 21:47:25




    ENABLED: 1

      TYPE: set_owner

    COMMENT: Total pages flushed as part of sync batches

1 row in set (0.001 sec)[/code]

I do not know how to proceed with troubleshooting it, could someone please advise?

Thanks! 😃

Best Answer


  • PeterPeter Percona CEO Percona Moderator Role


    My suggestion to troubleshoot data capture would be to select graph and press X or navigate to Explore Mode

    This will show you what formula is being graphed and when you can see in Advanced Data Exploration Dashboard whenever this metric is being captured

    That can help to see if it is a capture problem or display problem.

    You have the data in the database it is still a question whenever this data is being captured from exporter and stored in the PMM database - sometimes timeouts can cause data capture problems - This can be checked with Prometheus Exporter Status dashboard

    Re your particular MariaDB problem - I'd check if increasing your innodb_io_capacity and innodb_io_capacity_max will improve the situation

  • GorintherGorinther Current User Role Novice


    Thanks for your reply. That "explore" window I already tried going before, that's where I got the "mysql_info_schema_innodb_metrics_buffer_buffer_flush_adaptive_total_pages" name. However if I try to create a new query and start typing "mysql_info_schema_innodb_", after this I only have 10 suggestions as on the screenshot below:

    And none of them starts with "_metrics" - as soon as I type "_m" there is no suggestion anymore.

    I also tried going for that "Advanced Data Exploration" dashboard however there is no "innodb_metrics" at all:

    My Prometheus Exporter Status looks good aswell, I could even find execution times for "collect.info_schema.innodb_metrics" which I think should be what I am looking for:

    Any other ideas on how to proceed?


  • GorintherGorinther Current User Role Novice

    Thanks! This was exactly the issue, I tried changing for MySQL 8.0.21 and it has worked straight away:

    It's so bad to see the change from MySQL codebase causing those issues.

    Thanks again, I learned a lot with it :)

  • PeterPeter Percona CEO Percona Moderator Role

    Thanks @adivinho for finding the root cause.

    I wish MariaDB would have kept compatibility... though this problem should not be hard to fix.

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