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  1. Percona Monitoring and Management
  2. PMM-1805

Available Downtime before SST Required doesn't seem to be accurate

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    Details

    • Type: Bug
    • Status: Done
    • Priority: Medium
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 1.17.0
    • Component/s: Grafana Dashboards
    • Labels:
      None

      Description

      If you check, https://www.percona.com/blog/2014/09/08/calculate-correct-size-percona-xtradb-clusters-gcache/ , the gcache size per minute is calculated as:

      mysql> show global status like 'wsrep_received_bytes';
      show global status like 'wsrep_replicated_bytes';
      select sleep(60);
      show global status like 'wsrep_received_bytes';
      show global status like 'wsrep_replicated_bytes';

      Bytes per minute:

      (second wsrep_received_bytes – first wsrep_received_bytes) + (second wsrep_replicated_bytes – first wsrep_replicated_bytes)

      So, on my end the output is 22.3M where gcache.size is set to 128M:

      mysql> select ((12051007742-12027618634)+(957312-954712))/1024/1024;

      -------------------------------------------------------

      ((12051007742-12027618634)+(957312-954712))/1024/1024

      -------------------------------------------------------

                                                22.30807114

      -------------------------------------------------------

      So, on my end I have less than 5.74 minutes of downtime before SST will be used:

      mysql> select 128/22.30807114;

      -----------------

      128/22.30807114

      -----------------

                5.7378

      -----------------

      1 row in set (0.01 sec)

      But based on the graph, I have 1.2 days as specified on the attachment. But, based on my tests I really have around 5 minutes before SST will be chosen over IST.

      Please check if delta can be a substitute for rate because I get better estimates with it.

      mysql_galera_gcache_size_bytes{instance="pxc1"}/(delta(mysql_global_status_wsrep_replicated_bytes{instance="pxc1"}[5m])+delta(mysql_global_status_wsrep_received_bytes{instance="pxc1"}[5m])) * 300

       

       

       

       

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                • Assignee:
                  Unassigned
                  Reporter:
                  jaime.sicam@percona.com Jaime Sicam
                • Votes:
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                    Updated:
                    Resolved:

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                    Time Spent - 45 minutes
                    45m