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  1. Moodle
  2. MDL-20613

Database contention issue because mdl_user table is being continuously written to

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: Major
    • Resolution: Won't Fix
    • Affects Version/s: 1.9.5
    • Fix Version/s: None
    • Component/s: Database SQL/XMLDB
    • Labels:
      None
    • Affected Branches:
      MOODLE_19_STABLE

      Description

      As discussed in http://moodle.org/mod/forum/discuss.php?d=135455#p592874, I have reported that the fact that several fields mdl_user table get written to with updates to login time and ip addresses, database contention happens frequently in Moodle, leading to frequently hangups in the user experience.

      This happens whenever a long query takes place that involves the user table (a great many such queries do). Then if someone logins or has other logable activity, it will hang all access to Moodle until both the read and the update queries have completed. The problem is made worse if there are any corrupt indexes.

      Some developers believe that these things have been moved to other tables, but that is not the case. Some have said it affects only certain DB engines, but I am not sure which ones, and one of the most common ones used with installation instructions is such an engine.

      The solution would seem to be to move updates involving routine changes in the user table to another table as such fields would not be a routine part of many of the queries that take extensive time to execute.

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            Assignee:
            stronk7 Eloy Lafuente (stronk7)
            Reporter:
            ganderson Gary Anderson
            Participants:
            Component watchers:
            Andrew Nicols, Jun Pataleta, Michael Hawkins, Shamim Rezaie, Simey Lameze
            Votes:
            3 Vote for this issue
            Watchers:
            3 Start watching this issue

              Dates

              Created:
              Updated:
              Resolved: