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 JANUARY 14, 2016

Applies to:

Oracle Database - Enterprise Edition - Version 11.2.0.4 to 12.1.0.2 [Release 11.2 to 12.1]
Linux x86
Linux x86-64
Oracle Solaris on x86-64 (64-bit)
Oracle Solaris on SPARC (64-bit)

Symptoms

After the upgrade to 11.2.0.4 database release, in a database that is using flash card, getting in alert log file messages like:

and flash cache is disabled.

Changes

The messages were introduced in 11.2.0.4 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.

Cause

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