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Measurement Strategy

In this section we will make some remarks about our measurement strategy and its corresponding implications for the form and type of the test scripts.

As explained in the "Description" section. the measurements are started periodically. However, in a networked environment connections may become slow or even get lost. This may result in a much longer test time and in the worst scenario the test may even hung. We believe that it is important to differentiate between lost and bad connections. Therefore, we allow that the duration of the tests may last for some measurement periods. A just started measurement exits when it is detected that a previous test is still running.

To prevent that the tests will hung forever, the following measures are taken:

The following steps are taken too minimise the chance that a data file is damaged by the killing of a running test:

  1. Data to save are stored in a new data file. To keep the data file open as short as possible, the results of the tests are stored in memory as long as the tests are running. After the tests the data buffer is written as one large block.
  2. The current data file is moved to a backup file. This also allows that still open file descriptors, used in for instance a Web presentation, will keep on functioning correctly.
  3. Immediately after step 2. the new data file is moved to its destination name. This make the time that the data file is unavailable for the Web presentation as short as possible. However, when a data file could not be read the user is informed that the data file probably is unavailable for only a period. He/she is proposed to retry a reload.
  4. The next time a data file is opened by the measurement script to read the old results also in memory, the backup file is used when the original file was not available.

Of course these preventions are not completely failsafe. The data files where the data of the current week and the data of the last 7 days are stored have an acceptable chance of being damaged, because they are only open for a limited period (current week data), or the damages are disappearing soon (data of last 7 days). But in all mean data files the chances are cumulative because new data are always added to the current values. Therefore, there are dedicated scripts to recalculate the mean data files from the data files with weekly data. It is recommended to run these scripts regularly. See the "Scripts" section. See also the description of the available data files in the "Description" section.

To diminish the effects of corrupted data files, data in a bad format are ignored by the measurement scripts and by the Web presentation of the results. However, the existence some incorrect data can not be excluded completely. But in the bulk of the correct data they are probably not very striking.


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