Why do some AA tables have Cache Size as ZERO and unindexed Foreign keys

Document ID : KB000116798
Last Modified Date : 20/10/2018
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Example 1 - Note some sequences such as ARUDSUSERAUDITREFIDSEQ have Cache_Size set 
at 1000 but other tables ARRFCASEIDSEQUENCE have Cache_Size set to 0 - Please explain the reasoning. 

Example 2 - ARADMINCONFIG has a Foreign Key FK_ARADMIN_CFG that has no index defined. Customer requesting information if this is intentional as they would think indexing would benefit performance
Why do some AA tables have Cache_Size as 0 and also have unindexed  Foreign keys  ? 
Riskfort and Webfort
As part of 8.2.02 service pack, ARUDSUSERAUDITREFIDSEQ sequence is not used. The value for this is hard-coded because these are not used for any reports/transactions. Therefore ARUDSUSERAUDITREFIDSEQ sequence can be ignored.

Cache_Size of ZERO has been used for tables that are only rarely used during normal transaction processing. These specific tables are configured in accordance with the CA Risk Authentication rules; setting a non-zero a Cache_Size could lead to a transaction-related performance impact.  Basically such tables are accessed very rarely and there is almost no contention for such tabular data, so a non-zero Cache_Size is not needed. 

For the reasons above the Foreign Keys are not indexed.
Additional Information: