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  1. MariaDB Server
  2. MDEV-8872

Performance regressions with utf8mb4 vs utf8 in WordPress

        Details

        • Type: Bug
        • Status: Open
        • Priority: Major
        • Resolution: Unresolved
        • Affects Version/s: 10.0.21-galera
        • Fix Version/s: None
        • Component/s: Character Sets
        • Labels:
          None

          Description

          When switching tables from utf8 to utf8mb4, we're seeing fairly severe performance regressions - queries that used to run in microseconds, now taking 20 seconds to run.

          We've run some tests with query and index variations, or there's a summary here.

          For a direct comparison, see:
          utf8: https://travis-ci.org/tollmanz/utf8mb4-query-time/jobs/82864656
          utf8mb4: https://travis-ci.org/tollmanz/utf8mb4-query-time/jobs/82864660

          Here's the WordPress tracking ticket. Comment #2 notes that reducing the meta_key column length to 191 (to match the length of the prefix index) fixes the performance issue, but the utf8 character set doesn't have the same problem.

          The same behaviour occurs in MySQL, as well.

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                  • Assignee:
                    bar Alexander Barkov
                    Reporter:
                    pento Gary Pendergast
                  • Votes:
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                    • Created:
                      Updated: