Jade 1.0 Technical Note
Using Jade For Large Measurements
Jade has been designed and implemented to cope with almost any size measurement. However, although Jade Capture has virtually no limitations on the size of a measurement, Jade Viewer's performance with large measurements can be severely affected by the user's hardware. In fact both Jade Capture and Jade Viewer can only cope with a maximum of 1,073,741,824 samples - enough for 18 months' data at 20 samples per second! - (subject to there physically being enough room on the hard disk to store the data, of course!).
This document therefore explains what the performance limitations are on Jade Viewer and gives guidance on the issues concerning long measurements.
The issues described in this technical note are:
Note: This document is only relevant to Jade Viewer, Jade Capture has no performance limitations (other than the maximum limit mentioned above).
The recommendations given in the data sheets is that Jade Viewer requires a 386SX 25MHz processor or better, and a 486SX 33MHz is recommended. These should be taken as the minimum a user can run Jade Viewer on and if measurements are generally short (typically under 12 hours or a day at most), this specification should cause no problems. However, given the availability of much faster processors (for example, Pentium 120s) on cheap computers, users may wish to consider running Jade Viewer on a faster machine. Using the correct processor for the anticipated size of file can have dramatic consequences. For example, a one week measurement will take about two hours to load on the minimum specification of a 386SX 25 but can take less than ten minutes on a 486DX 100.
Length of a Measurement Session
When the user opens one or more measurement periods, Jade Viewer process the data and calculates the statistics. In particular, it has to calculate the Leqs for the chart which involve processor-intensive calculations. The processor speed will therefore have a direct influence on the speed with which the data is loaded, and by implication the amount of data the user is comfortable with loading.
The following table shows typical measurement sessions that can be loaded in under fifteen minutes using various processor speeds (note that figures below assume a sampling rate of ten samples per second).
Although the amount of available RAM has little effect on the time taken to load data, it does affect how much Jade Viewer averages the data on loading.
Before going much further, it is important to understand how Jade Viewer loads the data. If the data is too large to fit in memory (typically, over three hours on a computer with 4Mb or RAM), Jade Viewer averages the data (using Leqs) so that it will fit. For example, a seven-day measurement period represents over six million data samples (at 10 sample per second) and would need over 17Mb of available memory at the raw data (home) level - not an option on most current computers! As a result, the lowest level at which a seven-day period can be viewed is 10 or 15 seconds on a 4Mb computer and 2 seconds on a 16Mb computer. Obviously, the amount of memory has an influence on the detail at which the user can view the data.
The following table shows the highest resolution possible for various periods of data on both a 4Mb and a 16Mb computer.
Adjusting the RAM
By default, Jade Viewer uses only 15% of the available RAM to load the data for a single chart. In normal usage, this means that users can have several charts open simultaneously without running out of memory. However, if a user has a requirement to open charts that contain a large amount of data, this limit can be increased to any amount up to 50%. Obviously, this will restrict the number of charts that can be opened simultaneously, but this may be a price worth paying. The percentage of RAM used to open one chart can be set in the JADE.INI file.
Note: The effect of changing the percentage to 50% is to allow Jade Viewer to hold 2-3 times the number of data samples in memory. For example, a one-day measurement on a 16Mb will now have a maximum resolution of 0.1 second instead of 0.2 second as in the table above.
To change the memory percentage:
Users may find that the minimum size of measurement period offered in the Measurements dialog is too large. This may mean, for example, that opening even one period on a slow computer may take too long.
When the data folder for the measurement is opened in the Measurements dialog, Jade Viewer calculates the size of an individual period. The size of the measurement period is typically the period specified in the measurement profile in Jade Capture. However, two further things affect the actual size chosen by Jade Viewer:
Tip: Try to use small, but sensible, sampling periods in measurement profiles in Jade Capture and specify a count. For example, a sampling period of 1 hour with a count of 168 is preferable to using a single sampling period of 7 days (and it is more flexible too!).
Changing the JADE.INI file to allow more periods
To change the maximum number of periods allowed in one data folder:
A high sampling rate for a long measurement will, of course, generate a large number of data samples. For example, a seven-day measurement period at 10 samples per second would generate over six million data samples and a Jade measurement file of over 12Mb. Users may wish to consider using lower sampling rates - particularly if they prefer longer sampling periods in the measurement profile and are therefore unlikely to actually view the data at its raw (home) level. However, doing this does mean far less flexibility and may not be an option for most users.
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