Uploaded image for project: 'MariaDB Server'
  1. MariaDB Server
  2. MDEV-7662

Possible perf issue: handler objects are created for merged derived tables

    Details

    • Type: Bug
    • Status: Open (View Workflow)
    • Priority: Minor
    • Resolution: Unresolved
    • Affects Version/s: 5.5.42, 10.0.17
    • Fix Version/s: 10.1
    • Component/s: Optimizer
    • Labels:
      None

      Description

      This is a continuation of MDEV-7586.

      If one takes a basic testcase with a merged derived table (or a view):

      create table t2 (a int);
      insert into t2 values (1),(2),(3);
      create view v2 as select a from t2;
       
      select * from v2;

      they can see that the code calls create_tmp_table(... do_not_open=true. ...) for the derived table (or the merged view). This may add extra overhead (although we are not sure how much ATM).

      This effect was introduced in MariaDB 5.3, in this commit:

      igor@askmonty.org-20100526201818-en2jqo1p1t3hi3ra
      Igor Babaev <igor@askmonty.org>
      maria-5.3-mwl106
      Wed 2010-05-26 13:18:18 -0700
      MWL#106: Backport optimizations for derived tables and views.
      The main consolidated patch.

      MySQL 5.6 doesn't have this optimization, so they dont have this problem.

        Attachments

          Issue Links

            Activity

              People

              • Assignee:
                psergey Sergei Petrunia
                Reporter:
                psergey Sergei Petrunia
              • Votes:
                0 Vote for this issue
                Watchers:
                1 Start watching this issue

                Dates

                • Created:
                  Updated: