Uploaded image for project: 'MariaDB Server'
  1. MariaDB Server
  2. MDEV-7474

Semi-Join's DuplicateWeedout strategy skipped for some values of optimizer_search_depth

    XMLWordPrintable

    Details

      Description

      When "semijoin" is enabled via "optimizer_switch", data can be duplicated with certain values of "optimizer_search_depth".

      According to this documentation page:

      https://mariadb.com/kb/en/mariadb/documentation/managing-mariadb/optimization-and-tuning/query-optimizations/optimization-strategies/duplicateweedout-strategy/

      A DuplicateWeedout strategy is supposed to be implemented using temporary tables for semijoin queries. For some values of "optimizer_search_depth", this duplicate weedout step may not occur.

      Attached is the following:

      optimizer_search_depth_semijoin_data_setup.sql - A script that sets up a database and a few tables.

      optimizer_search_depth_semijoin_query_test.sql - A script that queries the tables to demonstrate the problem.

      optimizer_search_depth_semijoin_output.txt - Example execution of the scripts and their output.

        Attachments

          Activity

            People

            Assignee:
            psergey Sergei Petrunia
            Reporter:
            GeoffMontee Geoff Montee
            Votes:
            0 Vote for this issue
            Watchers:
            4 Start watching this issue

              Dates

              Created:
              Updated:
              Resolved: