InnoDB System Variables System Variable innodb_read_ahead_threshold Scope Global Dynamic Yes SET_VAR  Hint Applies No Type Integer Default Value 56 Minimum Value 0 Maximum Value 64 Command-Line Format --innodb-read-io-threads=# System Variable innodb_read_io_threads Scope Global Dynamic No SET_VAR  Hint Applies No Type Integer Default Value 4 Minimum Value 1 Maximum Value 64 Controls the sensitivity of linear read-ahead that  InnoDB  uses to prefetch pages into the buffer pool. If  InnoDB  reads at least  innodb_read_ahead_threshold  pages sequentially from an extent (64 pages), it initiates an asynchronous read for the entire following extent. The permissible range of values is 0 to 64. A value of 0 disables read-ahead. For the default of 56,  InnoDB  must read at least 56 pages sequentially from an extent to initiate an asynchronous read for the following extent. Knowing how many pages are read through the read-ahead mechanism, and how many of these pages are evicted from the buffer pool without ever being accessed, can be useful when fine-tuning the  innodb_read_ahead_threshold  setting.  SHOW ENGINE INNODB STATUS output displays counter information from the  Innodb_buffer_pool_read_ahead  and Innodb_buffer_pool_read_ahead_evicted  global status variables, which report the number of pages brought into the buffer pool by read-ahead requests, and the number of such pages evicted from the buffer pool without ever being accessed, respectively. The status variables report global values since the last server restart. SHOW ENGINE INNODB STATUS  also shows the rate at which the read-ahead pages are read and the rate at which such pages are evicted without being accessed. The per-second averages are based on the statistics collected since the last invocation of  SHOW ENGINE INNODB STATUS  and are displayed in the  BUFFER POOL AND MEMORY  section of the  SHOW ENGINE INNODB STATUS  output. For more information, see Section 15.8.3.4, “Configuring InnoDB Buffer Pool Prefetching (Read-Ahead)” . For general I/O tuning advice, see Section 8.5.8, “Optimizing InnoDB Disk I/O” . The number of I/O threads for read operations in  InnoDB . Its counterpart for write threads is innodb_write_io_threads . For more information, see Section 15.8.5, “Configuring the Number of 3276 • innodb_read_io_threads