Bug #56277 Improve Adaptive hash index scalability
Submitted: 26 Aug 2010 3:02
Reporter: Shannon Wade Email Updates:
Status: Verified Impact on me:
None 
Category:MySQL Server: InnoDB storage engine Severity:S4 (Feature request)
Version: OS:Any
Assigned to: CPU Architecture:Any

[26 Aug 2010 3:02] Shannon Wade
Description:
This bug mentions that adaptive hash scalability is improved in the plugin.

http://bugs.mysql.com/bug.php?id=26442

and is closed. It mentions that this has been addressed somewhat in the plugin. However there are reports that this also is still a point of contention on powerful multi-core , fast storage servers.

 An option was added to --skip-innodb-adaptive-hash-index, however this is a work around for the contention created by the global mutex, from out docs:

"
 adaptive hash index mechanism allows InnoDB to take advantage of large amounts of memory, something typically done only by database systems specifically designed for databases that reside entirely in memory. Normally, the automatic building and use of adaptive hash indexes will improve performance. However, sometimes, the read/write lock that guards access to the adaptive hash index may become a source of contention under heavy workloads, such as multiple concurrent joins.
"

How to repeat:
n/a

Suggested fix:
Re-arcitect how this works so that the read write lock contention is improved and scales in the future instead of disabling.
[19 Feb 2014 8:25] MySQL Verification Team
http://www.mysqlperformanceblog.com/2010/02/25/index-lock-and-adaptive-search-next-two-big