Using GeoServer 2.7.2. The documentation for controlling ID generation in spatial databases is incorrect in a small but very important detail.
The page in question is http://docs.geoserver.org/latest/en/user/data/database/primarykey.html
I spent hours chasing a problem that was based on the documented name for the Primary Key Metadata Table being listed as gt_pk_metadata_table which is not correct. This name appears in multiple places including example SQL but the actual name should be simply gt_pk_metadata (no _table).
I easily confirm this by creating gt_pk_metadata, while leaving the Primary Key Metadata for my Oracle NG store blank/unspecified. During geoserver startup I see the following message logged:
2015-09-23 07:18:05,345 DEBUG [geotools.jdbc] - Reading metadata table metadata: SELECT * FROM MYSCHEMA.GT_PK_METADATA…
And the settings in the table take effect, using the name gt_pk_metadata but not when using gt_pk_metadata_table.