interpolated_delta()

Early access 1.8.0

Calculate the change in a gauge over the time period covered by a gauge aggregate. Data points at the exact boundaries of the time period aren’t needed. The function interpolates the gauge values at the boundaries from adjacent gauge aggregates if needed.

Samples

Calculate the gauge delta for each 15-minute interval, using interpolation to get the values at the interval boundaries if they don’t exist in the data.

SELECT
    id,
    bucket,
    interpolated_delta(
        summary,
        bucket,
        '15 min',
        LAG(summary) OVER (PARTITION BY id ORDER by bucket),
        LEAD(summary) OVER (PARTITION BY id ORDER by bucket)
    )
FROM (
    SELECT
        id,
        time_bucket('15 min'::interval, ts) AS bucket,
        gauge_agg(ts, val) AS summary
    FROM foo
    GROUP BY id, time_bucket('15 min'::interval, ts)
) t

Arguments

The syntax is:

interpolated_delta(
    summary GaugeSummary,
    start TIMESTAMPTZ,
    interval INTERVAL
    [, prev GaugeSummary]
    [, next GaugeSummary]
) RETURNS DOUBLE PRECISION

Name	Type	Default	Required	Description
summary	GaugeSummary	-	✔	A gauge aggregate created using gauge_agg
start	TIMESTAMPTZ	-	✔	The start of the time period to compute the delta over
interval	INTERVAL	-	✔	The length of the time period to compute the delta over
prev	GaugeSummary	-		The gauge aggregate from the previous interval, used to interpolate the value at start. If NULL, the first timestamp in summary is used as the start of the interval.
next	GaugeSummary	-		The gauge aggregate from the next interval, used to interpolate the value at start + interval. If NULL, the last timestamp in summary is used as the end of the interval.

Returns

Column	Type	Description
interpolated_delta	DOUBLE PRECISION	The delta between the first and last points of the time interval. If exact values are missing in the raw data for the first and last points, these values are interpolated linearly from the neighboring gauge aggregates.