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(mysql.info.gz) Shared key cache

Info Catalog (mysql.info.gz) MyISAM key cache (mysql.info.gz) MyISAM key cache (mysql.info.gz) Multiple key caches
 
 7.4.6.1 Shared Key Cache Access
 ...............................
 
 Prior to MySQL 4.1, access to the key cache is serialized: No two
 threads can access key cache buffers simultaneously.  The server
 processes a request for an index block only after it has finished
 processing the previous request. As a result, a request for an index
 block not present in any key cache buffer blocks access by other
 threads while a buffer is being updated to contain the requested index
 block.
 
 Starting from version 4.1.0, the server supports shared access to the
 key cache:
 
    * A buffer that is not being updated can be accessed by multiple
      threads.
 
    * A buffer that is being updated causes threads that need to use it
      to wait until the update is complete.
 
    * Multiple threads can initiate requests that result in cache block
      replacements, as long as they do not interfere with each other
      (that is, as long as they need different index blocks, and thus
      cause different cache blocks to be replaced).
 
 
 Shared access to the key cache allows the server to improve throughput
 significantly.
 
Info Catalog (mysql.info.gz) MyISAM key cache (mysql.info.gz) MyISAM key cache (mysql.info.gz) Multiple key caches
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