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  1. MariaDB Server
  2. MDEV-31227

innodb_flush_method=O_DIRECT causes 3x regression in workload

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Details

    • Bug
    • Status: Closed (View Workflow)
    • Minor
    • Resolution: Not a Bug
    • 10.6.12, 10.6.13
    • N/A
    • None
    • CentOS 7, kernel 3.10

    Description

      Repro procedure is the same as MDEV-30567. Additional details for that in the comments.

      In short, this is the performance discrepancy we're seeing in 10.6.13 (10.6.12 performs similarly but slightly worse)-

      # Default (O_DIRECT)
      # * Q0: real: 14.21  min: 14.21  max: 14.21
       
      # innodb-flush-method = fsync
      # * Q0: real: 4.94  min: 4.94  max: 4.94
       
      # innodb-flush-method = O_DSYNC
      # * Q0: real: 4.92  min: 4.92  max: 4.92
       
      # innodb-flush-method = littlesync
      # * Q0: real: 4.91  min: 4.91  max: 4.91
       
      # innodb-flush-method = nosync
      # * Q0: real: 4.95  min: 4.95  max: 4.95
       
      # innodb-flush-method = O_DIRECT
      # * Q0: real: 14.21  min: 14.21  max: 14.21
       
      # innodb-flush-method = O_DIRECT_NO_FSYNC
      # * Q0: real: 12.81  min: 12.81  max: 12.81

      The customer for whom we are concerned about this issue for is currently using 10.4 where innodb_flush_method=fsync is the default. For 10.6 though, this changes to O_DIRECT. For now, we're advising the customer to hard-specify innodb_flush_method=fsync for 10.6. However, we know that O_DIRECT was made default in 10.6 as it generally improves over fsync, so we'd like to know if the regression we're seeing here is due to a bug that, if fixed, would make O_DIRECT the all-around ideal it is intended to be.

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              midenok Aleksey Midenkov
              rob.schwyzer@mariadb.com Rob Schwyzer
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                Updated:
                Resolved:

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