delay

Delays events relative to a given start time, with an optional speedup.

delay by:field, [start=time, speed=double]

Description

The delay operator replays a dataflow according to a time field by introducing sleeping periods proportional to the inter-arrival times of the events.

With the speed option, you can adjust the sleep time of the time series induced by by with a multiplicative factor. This has the effect of making the time series "faster" for values great than 1 and "slower" for values less than 1. Unless you provide a start time with start, the operator will anchor the timestamps in by to begin with the current wall clock time, as if you provided start=now().

The diagram below illustrates the effect of applying delay to dataflow. If an event in the stream has a timestamp the precedes the previous event, delay emits it instanstly. Otherwise delay sleeps the amount of time to reach the next timestamp. As shown in the last illustration, the speed factor has a scaling effect on the inter-arrival times.

The options start and speed work independently, i.e., you can use them separately or both together.

by: field

The field in the event containing the timestamp values.

start = time (optional)

The timestamp to anchor the time values around.

Defaults to the first non-null timestamp in field.

speed = double (optional)

A constant factor to be divided by the inter-arrival time. For example, 2.0 decreases the event gaps by a factor of two, resulting a twice as fast dataflow. A value of 0.1 creates dataflow that spans ten times the original time frame.

Defaults to 1.0.

Examples

Replay the M57 Zeek logs with real-world inter-arrival times from the ts field. For example, if an event arrives at time t and the next event at time u, then the delay operator will wait time u - t between emitting the two events. If t > u then the operator immediately emits next event.

load_http "https://storage.googleapis.com/tenzir-datasets/M57/zeek-all.log.zst"
read_zeek_tsv
delay ts

Replay the M57 Zeek logs at 10.5 times the original speed.

load_http "https://storage.googleapis.com/tenzir-datasets/M57/zeek-all.log.zst"
read_zeek_tsv
delay ts, speed=10.5

Replay as above, but start delaying only after ts exceeds 2021-11-17T16:35 and emit all events prior to that timestamp immediately.

load_file "https://storage.googleapis.com/tenzir-datasets/M57/zeek-all.log.zst"
read_zeek_tsv
delay ts, start=2021-11-17T16:35, speed=10.0

Adjust the timestamp to the present, and then start replaying in 2 hours from now:

load_file "https://storage.googleapis.com/tenzir-datasets/M57/zeek-all.log.zst"
decompress "zstd"
read_zeek_tsv
timeshift ts
delay ts, start=now()+2h