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  1. Percona Monitoring and Management
  2. PMM-5839

PostgreSQL metrics disparity between query time and block read/write time

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    Details

    • Type: Bug
    • Status: Done
    • Priority: Medium
    • Resolution: Fixed
    • Affects Version/s: 2.0.0
    • Fix Version/s: 2.7.0
    • Component/s: PMM Agent
    • Labels:
    • Story Points:
      1
    • Sprint:
      Platform Sprint 17, Platform Sprint 18
    • Needs Review:
      Yes
    • Needs QA:
      Yes

      Description

      As we discovered in  PMM-5698  + Puneet Kala investigation with  PG team : 

      We have metrics in PG and they are cumulative but by the data, we have in QAN - it looks like we treated them as data for current query or something like this  

      • 'blk_read_time',
      • 'blk_write_time',

       

      Because we had 'blk_*_time' metrics bigger than 'query time' 

       

      STR:
      1) Setup PostgreSQL 10.4 version and "create extension pg_stat_statements"
      2) Create database sbtest_pg
      3) run alter database sbtest_pg set track_io_timings=1;
      4) create user sbtest
      5) grant the user all privileges to sbtest_pg
      6) sysbench --db-driver=pgsql --oltp-table-size=100000 --oltp-tables-count=24 --threads=1 --pgsql-db=sbtest_pg --pgsql-user=sbtest --pgsql-host=localhost /usr/share/sysbench/tests/include/oltp_legacy/parallel_prepare.lua run
      7) sysbench --db-driver=pgsql --report-interval=2 --oltp-table-size=100000 --oltp-tables-count=24 --threads=32 --time=60 --pgsql-host=localhost --pgsql-port=5432 --pgsql-user=sbtest --pgsql-db=sbtest_pg /usr/share/sysbench/tests/include/oltp_legacy/oltp.lua run

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          118 kB
          Beata Handzelova
        2. image-2020-06-01-13-10-50-244.png
          118 kB
          Beata Handzelova
        3. image-2020-06-01-13-11-29-055.png
          140 kB
          Beata Handzelova

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              Assignee:
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              Reporter:
              roma.novikov Roma Novikov
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