JoinNode

Warning! This page documents an old version of Kapacitor, which is no longer actively developed. Kapacitor v1.4 is the most recent stable version of Kapacitor.

Joins the data from any number of nodes. As each data point is received from a parent node it is paired with the next data points from the other parent nodes with a matching timestamp. Each parent node contributes at most one point to each joined point. A tolerance can be supplied to join points that do not have perfectly aligned timestamps. Any points that fall within the tolerance are joined on the timestamp. If multiple points fall within the same tolerance window than they are joined in the order they arrive.

Aliases are used to prefix all fields from the respective nodes.

The join can be an inner or outer join, see the JoinNode.Fill property.

Example:

    var errors = stream
        |from()
            .measurement('errors')
    var requests = stream
        |from()
            .measurement('requests')
    // Join the errors and requests streams
    errors
        |join(requests)
            // Provide prefix names for the fields of the data points.
            .as('errors', 'requests')
            // points that are within 1 second are considered the same time.
            .tolerance(1s)
            // fill missing values with 0, implies outer join.
            .fill(0.0)
            // name the resulting stream
            .streamName('error_rate')
        // Both the "value" fields from each parent have been prefixed
        // with the respective names 'errors' and 'requests'.
        |eval(lambda: "errors.value" / "requests.value")
           .as('rate')
        ...

In the above example the errors and requests streams are joined and then transformed to calculate a combined field.

Index

Properties

Chaining Methods

Properties

Property methods modify state on the calling node. They do not add another node to the pipeline, and always return a reference to the calling node. Property methods are marked using the . operator.

As

Prefix names for all fields from the respective nodes. Each field from the parent nodes will be prefixed with the provided name and a '.'. See the example above.

The names cannot have a dot '.' character.

node.as(names ...string)

Fill

Fill the data. The fill option implies the type of join: inner or full outer Options are:

  • none - (default) skip rows where a point is missing, inner join.
  • null - fill missing points with null, full outer join.
  • Any numerical value - fill fields with given value, full outer join.
node.fill(value interface{})

On

Join on specific dimensions. For example given two measurements:

  1. building_power – tagged by building, value is the total power consumed by the building.
  2. floor_power – tagged by building and floor, values is the total power consumed by the floor.

You want to calculate the percentage of the total building power consumed by each floor.

Example:

    var buidling = stream
        |from()
            .measurement('building_power')
            .groupBy('building')
    var floor = stream
        |from()
            .measurement('floor_power')
            .groupBy('building', 'floor')
    building
        |join(floor)
            .as('building', 'floor')
            .on('building')
        |eval(lambda: "floor.value" / "building.value")
            ... // Values here are grouped by 'building' and 'floor'
node.on(dims ...string)

StreamName

The name of this new joined data stream. If empty the name of the left parent is used.

node.streamName(value string)

Tolerance

The maximum duration of time that two incoming points can be apart and still be considered to be equal in time. The joined data point's time will be rounded to the nearest multiple of the tolerance duration.

node.tolerance(value time.Duration)

Chaining Methods

Chaining methods create a new node in the pipeline as a child of the calling node. They do not modify the calling node. Chaining methods are marked using the | operator.

Alert

Create an alert node, which can trigger alerts.

node|alert()

Returns: AlertNode

Bottom

Select the bottom num points for field and sort by any extra tags or fields.

node|bottom(num int64, field string, fieldsAndTags ...string)

Returns: InfluxQLNode

Count

Count the number of points.

node|count(field string)

Returns: InfluxQLNode

Deadman

Helper function for creating an alert on low throughput, aka deadman's switch.

  • Threshold – trigger alert if throughput drops below threshold in points/interval.
  • Interval – how often to check the throughput.
  • Expressions – optional list of expressions to also evaluate. Useful for time of day alerting.

Example:

    var data = stream
        |from()...
    // Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
    data
        |deadman(100.0, 10s)
    //Do normal processing of data
    data...

The above is equivalent to this Example:

    var data = stream
        |from()...
    // Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
    data
        |stats(10s)
        |derivative('emitted')
            .unit(10s)
            .nonNegative()
        |alert()
            .id('node \'stream0\' in task \'{{ .TaskName }}\'')
            .message('{{ .ID }} is {{ if eq .Level "OK" }}alive{{ else }}dead{{ end }}: {{ index .Fields "emitted" | printf "%0.3f" }} points/10s.')
            .crit(lamdba: "emitted" <= 100.0)
    //Do normal processing of data
    data...

The id and message alert properties can be configured globally via the 'deadman' configuration section.

Since the AlertNode is the last piece it can be further modified as normal. Example:

    var data = stream
        |from()...
    // Trigger critical alert if the throughput drops below 100 points per 1s and checked every 10s.
    data
        |deadman(100.0, 10s)
            .slack()
            .channel('#dead_tasks')
    //Do normal processing of data
    data...

You can specify additional lambda expressions to further constrain when the deadman's switch is triggered. Example:

    var data = stream
        |from()...
    // Trigger critical alert if the throughput drops below 100 points per 10s and checked every 10s.
    // Only trigger the alert if the time of day is between 8am-5pm.
    data
        |deadman(100.0, 10s, lambda: hour("time") >= 8 AND hour("time") <= 17)
    //Do normal processing of data
    data...
node|deadman(threshold float64, interval time.Duration, expr ...tick.Node)

Returns: AlertNode

Default

Create a node that can set defaults for missing tags or fields.

node|default()

Returns: DefaultNode

Derivative

Create a new node that computes the derivative of adjacent points.

node|derivative(field string)

Returns: DerivativeNode

Distinct

Produce batch of only the distinct points.

node|distinct(field string)

Returns: InfluxQLNode

Elapsed

Compute the elapsed time between points

node|elapsed(field string, unit time.Duration)

Returns: InfluxQLNode

Eval

Create an eval node that will evaluate the given transformation function to each data point. A list of expressions may be provided and will be evaluated in the order they are given and results of previous expressions are made available to later expressions.

node|eval(expressions ...tick.Node)

Returns: EvalNode

First

Select the first point.

node|first(field string)

Returns: InfluxQLNode

GroupBy

Group the data by a set of tags.

Can pass literal * to group by all dimensions. Example:

    |groupBy(*)
node|groupBy(tag ...interface{})

Returns: GroupByNode

HttpOut

Create an http output node that caches the most recent data it has received. The cached data is available at the given endpoint. The endpoint is the relative path from the API endpoint of the running task. For example if the task endpoint is at "/api/v1/task/<task_name>" and endpoint is "top10", then the data can be requested from "/api/v1/task/<task_name>/top10".

node|httpOut(endpoint string)

Returns: HTTPOutNode

InfluxDBOut

Create an influxdb output node that will store the incoming data into InfluxDB.

node|influxDBOut()

Returns: InfluxDBOutNode

Join

Join this node with other nodes. The data is joined on timestamp.

node|join(others ...Node)

Returns: JoinNode

Last

Select the last point.

node|last(field string)

Returns: InfluxQLNode

Log

Create a node that logs all data it receives.

node|log()

Returns: LogNode

Max

Select the maximum point.

node|max(field string)

Returns: InfluxQLNode

Mean

Compute the mean of the data.

node|mean(field string)

Returns: InfluxQLNode

Median

Compute the median of the data. Note, this method is not a selector, if you want the median point use .percentile(field, 50.0).

node|median(field string)

Returns: InfluxQLNode

Min

Select the minimum point.

node|min(field string)

Returns: InfluxQLNode

Percentile

Select a point at the given percentile. This is a selector function, no interpolation between points is performed.

node|percentile(field string, percentile float64)

Returns: InfluxQLNode

Sample

Create a new node that samples the incoming points or batches.

One point will be emitted every count or duration specified.

node|sample(rate interface{})

Returns: SampleNode

Shift

Create a new node that shifts the incoming points or batches in time.

node|shift(shift time.Duration)

Returns: ShiftNode

Spread

Compute the difference between min and max points.

node|spread(field string)

Returns: InfluxQLNode

Stats

Create a new stream of data that contains the internal statistics of the node. The interval represents how often to emit the statistics based on real time. This means the interval time is independent of the times of the data points the source node is receiving.

node|stats(interval time.Duration)

Returns: StatsNode

Stddev

Compute the standard deviation.

node|stddev(field string)

Returns: InfluxQLNode

Sum

Compute the sum of all values.

node|sum(field string)

Returns: InfluxQLNode

Top

Select the top num points for field and sort by any extra tags or fields.

node|top(num int64, field string, fieldsAndTags ...string)

Returns: InfluxQLNode

Union

Perform the union of this node and all other given nodes.

node|union(node ...Node)

Returns: UnionNode

Where

Create a new node that filters the data stream by a given expression.

node|where(expression tick.Node)

Returns: WhereNode

Window

Create a new node that windows the stream by time.

NOTE: Window can only be applied to stream edges.

node|window()

Returns: WindowNode