Ludwig-Maximilians-Universität München, Institut für Informatik
Technical Report 94-16
- TITLE:
-
An Analysis of Schedules for Performing Multi-Page Requests
- DATE:
-
August 1994
- AUTHORS:
- Bernhard Seeger
<seeger@informatik.uni-muenchen.de>
- Institut für Informatik
- Universität München
- Leopoldstr. 11B
- D-80802 München (Germany)
- KEYWORDS:
-
I/O performance, multi-page requests, magnetic disk modelling,
cost functions, query optimization, throughput
- ABSTRACT:
-
In this paper, we address the problem of efficiently
reading a set of pages from a file
which is kept on some cylinders of a magnetic disk. It is
assumed that several pages can be read from disk in a single multi-page
request without interfering of other requests.
First, a simple algorithm is presented for computing a schedule how the
required pages are read from disk. Then, the expected cost of the schedules is
analyzed by using a pure analytical model. In addition to the
disk geometry, the analysis takes into account
the three major cost components (seek time, rotational delay and
transfer time) which occur when pages are retrieved from magnetic disk.
% Moreover, only the transfer time is assumed to be constant for all pages.
The derived cost function depends on two parameters:
disk geometry, the analysis takes into account
the three major cost components (seek time, rotational delay and
transfer time) which occur when pages are retrieved from magnetic disk.
The derived cost function depends on two parameters:
the number of required pages and
the degree of clustering of the underlying file.
The cost function demonstrates that
significant performance improvements can be achieved by using
multi-page requests when the required pages are read according to a
well-computed schedule.
In addition to the response time of an individual query,
we also examine the impact of multi-pages request on the throughput.
Results of an experimental performance comparison demonstrate that
the throughput can be improved considerably by several factors when
multi-page requests are used in comparison to reading the required pages
one at a time.
performance comparison demonstrate that
the throughput can be improved considerably by several factors when
multi-page requests are used in comparison to reading the required pages
one at a time.
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For problems and suggestions send an email message to
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Robert Stabl
(30.11.1994)