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  1. Percona Monitoring and Management
  2. PMM-7924

MySQL Performance Details dashboard: Add "Performance Schema Status Monitoring" chart

Details

    • New Feature
    • Status: Done
    • Medium
    • Resolution: Fixed
    • 2.15.1
    • 2.22.0
    • None
    • None

    Description

      User impact: User can't see statues of Performance schema variables

      TBD: Add "Performance Schema Status Monitoring" chart to MySQL Performance Details dashboard

      Original report: Hi,
       
      I was investigating an issue when queries did not show up in QAN. I was not 100% sure how PMM gets the queries from the Performance Schema, but after some digging it looks like it is using the events_statements_summary_by_digest. So I checked the queries manually and was not there and even if I was running any queries they did not went into that table... more digging etc.. long story short I realized that table has a limitation:
      mysql> select count from performance_schema.events_statements_summary_by_digest;
      ----------

      count

      ----------

      10000

      ----------
      1 row in set (0.04 sec)mysql> show global variables like '%performance_schema_digests_size%'
      -> ;
      --------------------------------------+

      Variable_name Value

      --------------------------------------+

      performance_schema_digests_size 10000

      --------------------------------------+
      1 row in set (0.00 sec)
      So basically QAN was not reporting any new queries because that table was already full. Millions of queries were lost from QAN:
      mysql> show global status like '%Performance_schema_digest_lost%';
      ----------------------------------------+

      Variable_name Value

      ----------------------------------------+

      Performance_schema_digest_lost 53757129

      ----------------------------------------+
      1 row in set (0.00 sec)
      Unfortunately increasing performance_schema_digests_size needs a restart.
      I have also checked PMM and did not find any information regarding to this.. Should not we let our customers now if the events_statements_summary_by_digest table is full they can miss many queries from QAN. This is a specially important table as our whole QAN based on this if I am right.
       

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              vadim.yalovets Vadim Yalovets
              tibor.korocz Tibor Korocz
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