Uploaded image for project: 'MariaDB ColumnStore'
  1. MariaDB ColumnStore
  2. MCOL-4849

Optimize ExeMgr to reduce a number of context switches

    XMLWordPrintable

Details

    • New Feature
    • Status: Closed (View Workflow)
    • Major
    • Resolution: Fixed
    • 6.1.1
    • 6.2.2
    • ExeMgr
    • None

    Description

      MCS generates enourmous amount of context switches that degrades performance a lot. The screenshoot cs.png demonstates this, namely cs number raises from ~80 to 21k once I run a single query(select l_orderkey, count(l_orderkey) from lineitem group by l_orderkey limit 10) in an infinite loop.
      According with the perf tool observations(collected with perf record --call-graph dwarf -e context-switches -p $(pidof ExeMgr) command) there are number of candidates for the optimization:

      • messageqcpp::InetStreamSocket::readToMagic() that both uses poll and reads a byte at a time increasing the number of cs needed.
      • joblist::TupleBPS::receiveMultiPrimitiveMessages() that contains a loop that processes intermediate RGData sent by PP to EM as results of Primitive requests. There are both mutex and conditional_variables widely used in TupleBPS methods's code.
      • joblist::FIFO<rowgroup::RGData>::swapBuffers() that leverages mutexes to save crit section of this RGData queue from TBPS to TAS.
        Plz take a look at perf.png for some details.
        The goal is to reduce a number of context switches produced by ExeMgr code. It is worth to have in mind that othere categories of queries might produce a different pattern. However the three parts mentioned affect every query b/c the are substantial to query processing.

      Attachments

        1. cs.png
          226 kB
          Roman
        2. graph.svg
          23 kB
          Denis Khalikov
        3. perf.png
          485 kB
          Roman
        4. profile.txt
          109 kB
          Denis Khalikov
        5. Screenshot from 2021-09-01 20-22-08.png
          119 kB
          Denis Khalikov

        Issue Links

          Activity

            People

              dleeyh Daniel Lee (Inactive)
              drrtuy Roman
              Votes:
              0 Vote for this issue
              Watchers:
              3 Start watching this issue

              Dates

                Created:
                Updated:
                Resolved:

                Git Integration

                  Error rendering 'com.xiplink.jira.git.jira_git_plugin:git-issue-webpanel'. Please contact your Jira administrators.