Uploaded image for project: 'MariaDB Server'
  1. MariaDB Server
  2. MDEV-38529

Background thread exhaustion upon CREATE GLOBAL TEMPORARY TABLE ... SELECT

    XMLWordPrintable

Details

    • Not for Release Notes

    Description

      INSTALL SONAME 'ha_federated';
      CREATE SERVER srv FOREIGN DATA WRAPPER mysql OPTIONS (SOCKET '../socket.sock', DATABASE 'test', USER 'root@localhost', PASSWORD '');
      CREATE TABLE t (c INT) CONNECTION='srv/t' ENGINE=Federated;
      CREATE GLOBAL TEMPORARY TABLE t1 (c INT) SELECT * FROM t;
      SHOW PROCESSLIST;
      

      Will get temporary stuck on the CREATE GLOBAL TEMPORARY and eventually fail with:

      MDEV-35915-v10b CS 12.2.0 86d9fd540eb171a739b72a4875ae3a92b33c212d (Debug, Clang 21.1.3-20250923) Build 10/01/2026

      12.2.0-dbg>CREATE GLOBAL TEMPORARY TABLE t1 (c INT) SELECT * FROM t;
      ERROR 1159 (08S01): Got timeout reading communication packets
      

      In the background, thousands of similar new background connections are being created:

      MDEV-35915-v10b CS 12.2.0 86d9fd540eb171a739b72a4875ae3a92b33c212d (Debug, Clang 21.1.3-20250923) Build 10/01/2026

      12.2.0-dbg>show processlist;
      +------+----------------------+-----------+------+---------+------+------------+----------------------------------------------------------+----------+
      | Id | User | Host      | db   | Command | Time | State    | Info             | Progress |
      +------+----------------------+-----------+------+---------+------+------------+----------------------------------------------------------+----------+
      ...
      | 2355 | root@localhost       | localhost | test | Query   |    0 |            | SHOW TABLE STATUS LIKE 't'                               |    0.000 |
      | 2356 | root@localhost       | localhost | test | Query   |    0 |            | SHOW TABLE STATUS LIKE 't'                               |    0.000 |
      | 2357 | root@localhost       | localhost | test | Query   |    0 |            | SHOW TABLE STATUS LIKE 't'                               |    0.000 |
      | 2358 | root@localhost       | localhost | test | Query   |    0 |            | SHOW TABLE STATUS LIKE 't'                               |    0.000 |
      | 2359 | root@localhost       | localhost | test | Query   |    0 |            | SHOW TABLE STATUS LIKE 't'                               |    0.000 |
      | 2360 | unauthenticated user | localhost | NULL | Connect |    0 | login      | NULL                                                     |    0.000 |
      +------+----------------------+-----------+------+---------+------+------------+----------------------------------------------------------+----------+
      2357 rows in set (0.016 sec)
      

      The connections do not dissapear and start accumulating time even after the failure. Furthermore, additional ones are constantly created.

      Attachments

        Activity

          People

            nikitamalyavin Nikita Malyavin
            Roel Roel Van de Paar
            Votes:
            0 Vote for this issue
            Watchers:
            2 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.