metricAggregator

The MetricAggregator

In some cases, further combination of metrics or raw values is required. For that strings like foo + 1 with runtime dependent foo need to be evaluated. The MetricAggregator relies on the gval Golang package to perform all expression evaluation. The gval package provides the basic arithmetic operations but the MetricAggregator defines additional ones.

Note: To get an impression which expressions can be handled by gval, see its README

Simple expression evaluation

For simple expression evaluation, the MetricAggregator provides two function for different use-cases:

• EvalBoolCondition(expression string, params map[string]interface{}: Used by the MetricRouter to match metrics like metric.Name() == 'mymetric'
• EvalFloat64Condition(expression string, params map[string]interface{}): Used by the MetricRouter and LikwidCollector to derive new values like (PMC0+PMC1)/PMC3

MetricAggregator extensions for gval

The MetricAggregator provides these functions additional to the Full language in gval:

• sum(array): Sum up values in an array like sum(values)
• min(array): Get the minimum value in an array like min(values)
• avg(array): Get the mean value in an array like avg(values)
• mean(array): Get the mean value in an array like mean(values)
• max(array): Get the maximum value in an array like max(values)
• len(array): Get the length of an array like len(values)
• median(array): Get the median value in an array like mean(values)
• in: Check existence in an array like 0 in getCpuList() to check whether there is an entry 0. Also substring matching works like temp in metric.Name()
• match: Regular-expression matching like match('temp_cores_%d+', metric.Name()). Note all \ in an regex has to be replaced with %
• getCpuCore(cpuid): For a CPU id, the the corresponding CPU core id like getCpuCore(0)
• getCpuSocket(cpuid): For a CPU id, the the corresponding CPU socket id
• getCpuNuma(cpuid): For a CPU id, the the corresponding NUMA domain id
• getCpuDie(cpuid): For a CPU id, the the corresponding CPU die id
• getSockCpuList(sockid): For a given CPU socket id, the list of CPU ids is returned like the CPUs on socket 1 getSockCpuList(1)
• getNumaCpuList(numaid): For a given NUMA node id, the list of CPU ids is returned
• getDieCpuList(dieid): For a given CPU die id, the list of CPU ids is returned
• getCoreCpuList(coreid): For a given CPU core id, the list of CPU ids is returned
• getCpuList: Get the list of all CPUs

Limitations

• Since the metrics are written in JSON files which do not allow "" without proper escaping inside of JSON strings, you have to use '' for strings.
• Since \ is interpreted by JSON as escape character, it cannot be used in metrics. But it is required to write regular expressions. So instead of /, use % and the MetricAggregator replaces them after reading the JSON file.