Tracker Examples

This article describes some simple tracker expressions.

Tracked Expression: aggregate("users.*.devices.*", "{env/previous} + ({.:status$connectionStatus} == 1 ? 1 : 0)", 0)

This expression uses aggregate() function to screen all device contexts (i.e. all contexts matching users.*.devices.* mask) and calculate those having connectionStatus field of the status variable equal to 1 (i.e. "online").

It will return number of online devices available to the user who owns the tracker. Thus, if executed with default administrator's permissions, it will return total number of online devices in the system.

Tracked Expression: round(({:status$totalMemory} - {:status$freeMemory}) * 100 / {:status$maxMemory})

First, amount of memory currently used by the Java VM is calculated by taking current allocation size and subtracting its free part.

Second, the above number is divided by the maximum memory size that the JVM is allowed to allocate. This gives the relative memory usage that is multiplied by 100 to calculate the percentage.

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