MySQL Performance Periodically Slows Down when using Certain RAID Hardware Controllers (Doc ID 1462128.1)

Last updated on APRIL 02, 2017

Applies to:

MySQL Server - Version 5.1 and later
Information in this document applies to any platform.
Definition of Autolearn feature
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Before a battery backup unit (BBU) can be used, it has to be calibrated. Until this calibration is done, controller will not use the BBU and instead will disable WriteBack cache on any logical drive. The controller does this for data integrity reasons which can also cause performance issues. The calibration process is a simple three step process where the controller determines maximum and minimum voltages and then sets BBU to maximum, fills the cache and then discharges it again. This process is usually done every 30 or 90 days depending on the make and model of the hardware in question.

Symptoms

On : 5.1 version, Other Technical Problem

ACTUAL BEHAVIOR
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Periodically the transactions will be very slow within the MySQL service whereas they are normally quite fast.

EXPECTED BEHAVIOR
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Transactions are expected to be relatively consistent in speed.


BUSINESS IMPACT
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The issue has the following business impact:
Due to this issue, users are held up as queries start to queue and response times lag.

Changes

 System log will show lines similar to the following when the autolearn feature is initiated:

Apr 26 12:55:31 b008 Server Administrator: Storage Service EventID: 2176  The controller battery Learn cycle has started.:  Battery 0 Controller 0
Apr 26 12:56:36 b008 Server Administrator: Storage Service EventID: 2266  Controller log file entry: Battery is discharging:  Battery 0 Controller 0
Apr 26 12:56:36 b008 Server Administrator: Storage Service EventID: 2248  The controller battery is executing a Learn cycle.:  Battery 0 Controller 0
Apr 26 14:21:52 b008 Server Administrator: Storage Service EventID: 2278  The controller battery charge level is below a normal threshold.:  Battery 0 Controller 0
Apr 26 14:21:53 b008 Server Administrator: Storage Service EventID: 2188  The controller write policy has been changed to Write Through.:  Battery 0 Controller 0
Apr 26 14:21:53 b008 Server Administrator: Storage Service EventID: 2199  The virtual disk cache policy has changed.:  Virtual Disk 0 (Virtual Disk 0) Controller 0 (PERC 6/i Adapter)

Cause

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