db flash cache is not being used

Flash cache can't be 100% fully utilized (Doc ID 1490043.1)

Flash cache is configured, but not 100% used. Only 1% of the configured flash cache size can be used.

Example:
Following settings are configured to make use of 4GB flash cache

*.db_block_size=32768
*.db_flash_cache_file='/dev/md/rdsk/d29'


However, below SQL output indicates that only 22338 flash blocks are used (32KB for every block, so around 700MB in total).

SQL> connect / as sysdba

SQL> select owner || '.' || object_name object,
     sum(case when b.status like 'flash%' then 1 end) flash_blocks,
     sum(case when b.status like 'flash%' then 0 else 1 END) cache_blocks,
     count(*) total_cached_blocks
     from v$bh b JOIN dba_objects o
     ON (objd = object_id)
     where owner NOT LIKE 'SYS%'
     group by owner, object_name
     having sum(case when b.status like 'flash%' then 1 end) > 0
     order by 4 desc;

CAUSE

This issue is due to
Bug 13935151 - ONLY ABLE TO USE 1% OF THE FLASH CACHE CONFIGURED, fixed in 12.1

SOLUTION

Apply Patch 13935151 if available for your DBVersion/platform

- OR -

Modify the below parameters manually in spfile/pfile:

_db_flash_cache_keep_limit=80
_db_flash_cache_write_limit=1