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Flash Cache Disabled After "Flash Cache: maximum number of slow reads .. exceeded the threshold ..." Messages in Alert Log File (Doc ID 2092059.1)

Last updated on FEBRUARY 18, 2019

Applies to:

Oracle Database - Enterprise Edition - Version to [Release 11.2 to 12.1]
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Backup Service - Version N/A and later
Linux x86
Linux x86-64
Oracle Solaris on x86-64 (64-bit)
Oracle Solaris on SPARC (64-bit)


After the upgrade to database release, in a database that is using flash card, getting in alert log file messages like:

and flash cache is disabled.


The messages were introduced in database code by the fix of:
<Bug 12874937>- Performance affected by faults in flash cache.

There were added in code checks to handle very slow flash I/O (for now at single block flash read as it is the most common place). The default is to disable flash cache after seeing 3 reads more than 2000 ms (2 seconds). Auto disabling of flash cache is a feature to contain the database performance in case there is defective flash cache and it is useless to waste time reading buffer from there when same buffer could have been read faster from the disk.


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