Variables, Substitution, and Assignment › Vartable Facility › Update Mirrored Vartables

Update Mirrored Vartables

When a new entry is added to the mirrored vartable by an NCL procedure, the new entry is automatically copied into the mirrored copy of the table.

The mirrored copy contains the following:

• A copy of the key (always 16 characters)
• A copy of the first 8 bytes of the DATA1 data field (blank padded if necessary)
• The .AOMID attribute
• An encoded version of the .AOMATTR attribute string
• A counter field .AOMCOUNT

When an existing entry is updated or deleted, the appropriate action is also performed on the mirrored copy. The screening table LOOKUP statement cannot update data in an entry, or delete an entry, but can update the count field in the mirrored entry.

When a screening table LOOKUP statement adds a new entry, the downward mirroring is not performed immediately, but is performed as soon as is necessary. This happens when:

• &VARTABLE GET retrieves an entry with that key value.
• The entry can be sequentially accessed.
• GET OPT=FIRST or LAST is specified. In this instance all pending mirroring is performed immediately.

These rules allow the mirrored copy of the vartable to be accessed with no serialization. This enhances the performance of the screening table.