Hash keys are often used as primary keys in Data Vault environments. When loading dimensional data marts from a Data Vault schema, it seems to be obvious to use them as dimension keys, too. At least in combination with Oracle Database In-Memory, this is not a good idea.
With Oracle Database In-Memory, it is possible to populate individual columns of a table into the In-Memory Column Store. This is very useful for large tables, if only the frequently used columns should be populated to safe memory. The SQL syntax to define this seems to be straight-forward, but does not always work as expected.
Virtual Columns in Oracle are a convenient feature to implement derived measures of a fact table. But in combination with Oracle Database In-Memory, it has an impact on performance – unless you use Oracle 12c Release 2.