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  1. MariaDB Server
  2. MDEV-18698

Show InnoDB's internal background threads in SHOW ENGINE INNODB STATUS

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      Description

      InnoDB uses internal background threads for a few different things. For example:

      • It uses a background thread to update persistent statistics.
      • It uses one or more background threads (determined by innodb_encryption_threads) to encrypt/decrypt tables where ENCRYPTED=DEFAULT.

      https://mariadb.com/kb/en/library/innodb-system-variables/#innodb_encryption_threads

      • It uses one or more background threads (determined by innodb_purge_threads) to purge unneeded undo logs.

      https://mariadb.com/kb/en/library/innodb-system-variables/#innodb_purge_threads

      • It uses one or more background threads (determined by either innodb_mtflush_threads or innodb_page_cleaners) to flush dirty pages from the buffer pool.

      https://mariadb.com/kb/en/library/innodb-system-variables/#innodb_mtflush_threads

      https://mariadb.com/kb/en/library/innodb-system-variables/#innodb_page_cleaners

      • It uses one or more background threads (determined by innodb_read_io_threads) to read pages from disk.

      https://mariadb.com/kb/en/library/innodb-system-variables/#innodb_read_io_threads

      • It uses one or more background threads (determined by innodb_write_io_threads) to write pages to disk.

      https://mariadb.com/kb/en/library/innodb-system-variables/#innodb_write_io_threads

      • Supposedly it uses some kind of background thread to implement some kind of "DROP TABLE" queue (based on the comments of MDEV-8069).

      It would probably make sense to show some or all of these threads in SHOW ENGINE INNODB STATUS output, since they can hold semaphores and cause or exacerbate concurrency issues.

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              Assignee:
              marko Marko Mäkelä
              Reporter:
              GeoffMontee Geoff Montee
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                Created:
                Updated: