SQL/MX 2.x Reference Manual (H06.04+)

SQL/MX File Attributes
HP NonStop SQL/MX Reference Manual—540440-003
8-5
CLEARONPURGE
CLEARONPURGE
The CLEARONPURGE file attribute controls erasure of data from the disk when a file
is deleted.
You set the CLEARONPURGE attribute for an SQL/MX table with CREATE TABLE or
ALTER TABLE. You set the CLEARONPURGE attribute for an SQL/MX index with
CREATE INDEX or ALTER INDEX.
The table default is NO CLEARONPURGE. The index default for the
CLEARONPURGE attribute is the table value at index creation. If the
CLEARONPURGE file attribute is changed on the base table, that change is
automatically propagated to the index.
Considerations for CLEARONPURGE
Purpose of CLEARONPURGE
When you drop or purge a table or index with NO CLEARONPURGE,
NonStop SQL/MX deallocates disk space but does not physically destroy the data in
that disk space. This implementation improves performance by reducing writes to the
disk, but when the disk space is allocated to a new file, other users might be able to
read data left by the object that used the space previously.
CLEARONPURGE increases security for sensitive data by causing the system to
overwrite deallocated disk space.
Effect Within Transactions
If you drop or purge a file with the CLEARONPURGE attribute from within a TMF
transaction, the data is not physically erased from the disk until after the transaction
commits.
CLEARONPURGE | NO CLEARONPURGE