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parameters
. For example, if the job processes a
file sequentially but from a certain point it will
take much more (or less) time to process a data
block and the analyser will decide that the strategy
has been changed, the new method will be still
increasing sequential
but with different timing
characteristics.
The file access method is determined in the
following way:
•
datablock log size: Determines how pre-
cise the access and intersection ratio will
be. The access and intersection ratios are
calculated by registering (per-file) the past
few datablocks accessed by the job.
Generating Complex
Job Descriptions
The generation of complex job descriptions is
based on two different approaches. These will
be presented in the following subsections along
with the algorithm implemented by the
descrip-
tion repository service
, which combines them.
•
The method is
increasing sequential
if
the maximum position has changed more
times than a threshold value (e.g. if the ac-
cess log size is 10, and the threshold is 7,
the maximum position has to be updated
8 times after processing 10 file operations
related to the given file).
Single Generalized Description
•
The method is
decreasing sequential
if the
minimum position has changed more times
than a threshold value.
The algorithm used by the
analyser sub-component
can be generalized to provide a refined description
that conforms to all previous executions of the
given job. According to the technique of the single
generalized description, the job description cannot
exclude an already completed sequence of opera-
tions. Therefore, the refinement of the description
mostly will lead to the relaxation of the behaviour
description. For example, if sometimes the job
processes a file sequentially and other times the
job processes it randomly, then the job description
cannot state that the file is processed sequentially,
because that would exclude the executions with
random file processing. Therefore the description
must state that the file access strategy is random.
However, the parameters of the random behaviour
description must not contradict with the parameters
of the sequential behaviour (e.g. block size).
The algorithm of refining a ”
simple”
job
description is as follows. Let us presume that we
have a job description that conforms to all previous
job descriptions and reflects the job behaviour as
close as possible. Let us also presume that after
running the job again, the generator provides a
new description that differs from the current one.
The following derivation rules define the basic
elements of job description refining:
•
Otherwise the method is
random
.
After the method has been determined, when-
ever a new file operation is processed, the analy-
ser updates the access log and the characteristic
parameters and checks if the actual file access
method has changed.
The analyser algorithm has several parameters,
which determine how detailed the resulting
file
access description
will be:
•
access log size: Specifies how deeply the
analyser can look into the past. The larger
this parameter the less detailed the descrip-
tion is.
•
progress detection threshold: Specifies
how many times the maximum (minimum)
position has to be changed in order to de-
tect the increasing (decreasing) sequential
access.
•
behaviour parameter variation: Determines
the scale by which the behaviour param-
eters can change.
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