Syntax for defining timeInterval windows

The syntax for the timeInterval window clause.

Note: TimeInterval windows do not support partition eviction.

Wname

Specifies the ID of the operator port connected to the window.

timeInterval

Specifies that the window-kind tuples are placed into panes which correspond to equal intervals in the event-time domain. A pane includes tuples with an event time greater or equal to the start time of the pane and lower than the end time.

intervalDuration(value)

Specifies the required duration between the lower and upper interval endpoints. It must be greater than zero (0.0).

creationPeriod(value)

Specifies the duration between adjacent intervals. The default value is equal to intervalDuration. It must be greater than zero (0.0).

discardAge(value)

Defines the duration between the point in time when a window pane becomes complete and the point in time when the window does not accept late tuples any longer. It must be greater or equal to zero (0.0). The default value is zero (0.0).

Note: Tuples which arrive later (with respect to the current watermark) than the discarding age value are ignored. Closed panes are deleted.

intervalOffset(value)

Defines a point-in-time value which coincides with an interval start time. Panes partition the event time domain into intervals of the form:

[N * creationPeriod + intervalOffset, N * creationPeriod + intervalDuration + intervalOffset)

where 0.0 is the Unix Epoch: 1970-01-01T00:00:00Z UTC.

The value must be in the interval [0.0, intervalDuration).

The value parameters above represent seconds, regardless of the type and the resolution of the event-time attribute.

Leap seconds

Calculations of the duration between two points in time take the difference between the two Unix time numbers. Calculations give the wrong result if leap seconds occur. For example, set up the following window clause to calculate one hour aggregates every 20 minutes for events starting at the beginning of the hour:

window W: timeInterval, intervalDuration(3600.0), creationPeriod(1200.0)

The system creates windows 00:00:00 to 01:00:00, 00:20:00 to 01:20:00, 00:40:00 to 01:40:00, and so on. The first window after a leap_second occurs might have a duration of 3601 seconds, although the subtraction of intervalEnd() minus intervalStart() is still 3600 because of the Unix time second adjustment.

Note: If the computer time works on UTC-SLS the extra second is uniformly spread over the last 1000 seconds of a UTC day that ends with a leap second.

Default trigger policy

When the current event time, which is specified by the watermark, becomes greater than or equal to the interval's end, the window pane becomes complete and triggers. If tuples with event times within the pane’s interval arrive after the pane has triggered (late tuples), the pane triggers again and the operator which handles the trigger event re-calculates output taking into account the late data. This means that a window pane which has received late data (late tuples) triggers again when the operator's watermark is updated.

When a pane triggers, the event handler calculates aggregate values based on the pane content.

Example of a traffic flow

The following example defines the maximum traffic flow over each freeway using event-time intervals of 50 seconds which slide every 25 seconds.


// Get maximum traffic flow over each freeway, over event-time intervals of
// size 50 seconds which slide every 25 seconds.
stream<TrafficInfo> MaxFlow = Aggregate(Traffic) {
    window PreWork : timeInterval, intervalDuration(50.0), intervalOffset(0.0), 
                     discardAge(1000.0), creationPeriod(25.0), partitioned;
    param partitionBy : freeway;
    output MaxFlow :
        timeStart = intervalStart(),
        timeEnd = intervalEnd(),
        freeway = ArgMax(laneFlow, freeway),
        eventtime = ArgMax(laneFlow, eventtime),
        laneFlow = Max(laneFlow);
}

Example of an adjacent time intervals of the duration of one hour

The following example defines adjacent time intervals of the duration of one hour, starting at the beginning of the hour:[00:20 .. 01:20), [01:20 .. 02:20), and so on.

Note: Intervals start at 00:30 in time zones with fractional hour offset such as India (+5:30).

window W: timeInterval intervalDuration(3600.0), intervalOffset(1200.0)

Example of intervals of the duration of one hour

The following example defines intervals of the duration of one hour, starting at the beginning of the hour and every 20 minutes after that: [00:00 .. 01:00),

[00:20 ..
01:20)

, and so on.

Note: Intervals start at 00:30 in time zones with fractional hour offset such as Iran (+3:30) or Venezuela (-4:30).

window W: timeInterval intervalDuration(hours(1)), creationPeriod(minutes(20), discardAge(hours(6))

Note:

The parameter values are expressed using functions defined in the com.teracloud.streamsx.datetime toolkit.
The discard age is six hours. If a tuple with time 00:00 arrives at the window before watermark 07:00, the tuple is inserted into interval [00:00 .. 01:00) and others, and processed as a late tuple. The tuple is discarded if it arrives after watermark 07:00.