The number of device feeds and the data buffer
3.1.7 Retry count:
The retry count specifies how many times the Web-Logger should retry obtaining the data from the
device after a timeout has occurred. The Web-Logger will re-request the data from the device
consecutively until a successful data request has occurred or until the number of re-tries are
exceeded.
Click "Save" to add the device.
Repeat these steps for each device feed you want to add.
3.2
Avoiding data request delays:
A data request delay occurs when the time it takes to request data from all the listed device feeds
takes longer to acquire than the set request interval on a single device.
For example, assuming the following configuration has been captured for each device feed:
Number of device feeds
: 10
Request Interval
: 5 seconds
Timeout value
: 500ms (0.5 seconds)
Retry count
: 3
In order to obtain the data for all the listed device feeds, assuming each device responds within
300ms, it would take in total:
10 device feeds x 300ms = 3000ms (3 seconds)
Assuming one of the devices that has 3 device feeds set, is not connected and causes a timeout. The
retry count of 3 has been set. The time it takes to query this specific device will then be:
3 retries x 500ms = 1500ms x 3 feeds = 4500ms (4.5 seconds)
The total time to obtain data from all the devices would then be as follows:
9 device feeds x 100ms
= 900ms
1 time out device
= 4500ms
= 5400ms (5.4 seconds)
The total time exceeds the 5 second interval selected initially. This will cause the Web-logger to take
longer than expected to process the list of device feeds and will result in the data not being sampled
every 5 seconds.
In order to correct this situation:
1. Attend to the non-communication device
2. Lower the timeout
3. Lower the retry count
4. Extend the request interval
4.
The number of device feeds and the data buffer
The number of device feeds as well as their request interval and the upload interval of the Web-
Logger will determine how quickly the Web-Logger buffer will be filled up
As per the above example, if you have 10 device feeds set to request every 5 seconds, a total of 10
data samples will be buffered every 5 seconds. If the upload interval is set to every 1 minute, a total
of 120 data samples will be stored in the buffer:
Total requests per device feed in 1 minute:
