IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Hardware & Software Remarks
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S 4.70 Monitoring a database
Initiation responsibility: Head of IT Section, IT Security Management
Implementation responsibility: Administrators
Databases should be monitored regularly to ensure the availability, integrity
and confidentiality of their data. The essential items which need to be
observed in this respect are described briefly in the following.
The database should be checked for fragmentation at regular intervals in order
to permit a timely planning and implementation of any required measures such
as reorganisation of the database.
As a rule, database systems manage the memory available to them in the form
of blocks having a fixed size. If data records are inserted into an empty table,
new blocks are reserved for this table and filled with the data records. These
newly created blocks can be utilised almost fully (with the exception of the
last block).
If data records are deleted during subsequent operation, the memory blocks
which were occupied by them are released. In principle, this memory space
can be used by other data records. However, as the data records have different
lengths, 100% utilisation of the free memory space is usually not possible.
Consequently, modifications to data in the course of time result in an
increasing number of gaps in the database blocks, most of which can no longer
be utilised. Such gaps are created not only by DELETE- and INSERT
operations but also by UPDATEs, as a data record can no longer be stored at
the same location once its length has been changed.
The presence of such gaps not only increases memory requirements but also
retards the operation of the database, as more disk space needs to be covered
in search of data records and free memory.
The degree of fragmentation in the blocks of a table can be ascertained by
comparing the quantity of data in the data records of the table with the
memory space occupied by the blocks of the table. In the case of certain
database management systems, an analysis of the degree of fragmentation is
also supported by the accompanying administration software or add-ons.
If a database becomes excessively fragmented due to the scenario mentioned
above, a reorganisation needs to be performed. This can be done manually, for
example, by exporting all the data out of the database, re-computing and recreating
all the tables, and then importing the data back into the new database.
Auxiliary programs for de-fragmenting tables are also available for some
database management systems.
Similarly, the available space of the database files should be checked regularly
in order to permit a timely planning and implementation of any required
measures such as the extension of the memory capacity. Some database
management systems allow administrators to prevent excessively rapid
fragmentation by already defining certain parameters during the creation of
the tables. For instance, it is possible to reserve a particular number of
consecutive blocks for a table in advance, to save free memory for any
changes required during later operation.
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IT-Baseline Protection Manual: Oktober 2000