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  1. MariaDB Server
  2. MDEV-26760

Galera hangs during concurrent updates



    • Type: Bug
    • Status: Closed (View Workflow)
    • Priority: Blocker
    • Resolution: Fixed
    • Affects Version/s: 10.4.18
    • Fix Version/s: 10.5.5, 10.4.22
    • Component/s: Galera
    • Labels:
    • Environment:
      CentOS 7.8



      I have a setup with 3 Galera nodes on MariaDB 10.4.18.
      I have blocking issue with MariaDB stability during concurrent updates on same row (this usually happens for me when multiple client applications tries to modify a record in the database in the same time).

      The issues is the following:
      1. Multiple customers starts the application and tries to perform an update on the same record.
      2. Galera handles a few concurrencies but eventually hangs.

      Now, I understand that we need to retry the transaction in the case of a deadlock, the issue is that Galera hangs before the application retries that.

      In order to replicate this we perform the following test:
      1. Start Galera on 3 nodes
      2. Have a ProxySQL with 3 nodes as writers
      3. We have a tool that connects to Galera start a tool that sends queries continuously to the database

      I'm attaching the script that we use testing and also I'm putting here he Galera configuration:

      • MariaDB validation diagram.png - This is the network topology for testing
      • MariaDB-server.cnf
      • galera-lock-replication.sql - SQLs to create the database and table for testing
      • galera-lock-replication.php - the tool that connects to database and send sql update
      • threads-tool.php - the tool that starts "galera-lock-replication.php" in multithreading mode to simulate concurrency

      Issue replication

      1. Create the database using the galera-lock-replication.sql script provided in attach

      2. Copy the 2 php files (galera-lock-replication.php and threads-tool.php) provided in attach in /galera-test/ folder under apache root

      3. Start a first terminal with:

      # php /path/to/galera-test/threads-tool.php

      • this will start bulks of 100 paralel calls to the frontend webservice in a loop:

      4. Wait few seconds (between 5 and 20)

      5. Galera cluster should start refuse connections


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              jplindst Jan Lindström
              ionut.andras Andras Marinescu
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