4…Choosing a Suitable Partitioning Strategy
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9.5 Self Test Questions
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3. Partitioning Strategy for Load Balancing
Which partitioning type is suited best to achieve fair load-balancing if the
values of the column are non-uniformly distributed?
(a) Partitioning based on the number of attributes used modulo the number of
systems
(b) Range Partitioning
(c) Round Robin Partitioning
(d) All partitioning types will show the same performance.
Reference
[Kar72] R. Karp, Reducibility among combinatorial problems, in Complexity of Computer
Computations, eds. by R. Miller, J. Thatcher (Plenum Press, 1972), pp. 85–103
Part III
In-Memory Database Operators
Chapter 10
Delete
The delete operation terminates the validity of a given tuple. It stores the information in the database that a certain item is no longer valid This operation can
either be of physical or logical nature. A physical delete operation removes an item
from the database so that it is no longer physically accessible. In contrast, a logical
delete operation only terminates the validity of an item in the dataset, but keeps the
tuple still available for temporal queries [Pla09].
The simplified SQL-Syntax for a delete statement looks like the following,
where the predicate may select a single or multiple tuples.
Listing 10.1: Delete syntax
10.1 Example of Physical Delete
In the following example, all persons with the name ‘Jane Doe’ are supposed to be
removed from a database table storing first and last names. Based on the applied
dictionary encoding (see Chap. 6), the table consists of two dictionaries and two
value attribute vectors.
First, the valueIDs for the first and last name need to be identified. Jane corresponds to valueID 23 and Doe to valueID 18, according to their respective dictionary.
H. Plattner, A Course in In-Memory Data Management,
DOI: 10.1007/978-3-642-36524-9_10, Ó Springer-Verlag Berlin Heidelberg 2013
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10
Delete
Next, we scan through the attribute vectors and find the appropriate positions,
which means we look up the recordIDs for these values. In our example, there is
only one tuple with that combination of first and last name.
When finally deleting the two values from the attribute vectors, all subsequent
tuples need to be adjusted to maintain a sequence without gaps and they are moved to
preserve a sequential memory area. This implementation alternative of the delete
operation is therefore very expensive in terms of performance. In Chap. 26, later
during the course, the insert-only approach is presented as a better alternative to
implement deletion in typical enterprise use cases. This approach is of logical nature.
