Flow control timeline

The same fifteen events arrive in bursts over a minute. Pick a kind of flow control and change its settings to see which runs start at once, which wait, which are skipped and which are merged.

Flow control

ConcurrencyThrottleRate limitDebounce

Concurrency

At most a number of runs execute at the same time. Others wait for a free slot and start in order. Concurrency in the Inngest docs.

Settings

Limit: 2Run duration: 8s

15 events, 15 runs, 13 delayed by up to 20s.started at oncedelayedskippedmerged into a later run

The numbers

Event arrives	Outcome	Its run starts
0s	started at once	0s
1s	started at once	1s
1.5s	delayed	8s
2s	delayed	9s
3s	delayed	16s
4s	delayed	17s
10s	delayed	24s
11s	delayed	25s
12s	delayed	32s
13s	delayed	33s
25s	delayed	40s
26s	delayed	41s
40s	delayed	48s
41s	delayed	49s
42s	delayed	56s

Throttle

At most a number of runs start per period. Others are queued and start later, spread out evenly. Throttle in the Inngest docs.

Settings

Limit: 3Period: 10sBurst: 0

15 events, 15 runs, 13 delayed by up to 17.0s.started at oncedelayedskippedmerged into a later run

The numbers

Event arrives	Outcome	Its run starts
0s	started at once	0s
1s	delayed	3.3s
1.5s	delayed	6.7s
2s	delayed	10s
3s	delayed	13.3s
4s	delayed	16.7s
10s	delayed	20s
11s	delayed	23.3s
12s	delayed	26.7s
13s	delayed	30.0s
25s	delayed	33.3s
26s	delayed	36.7s
40s	started at once	40s
41s	delayed	43.3s
42s	delayed	46.7s

Rate limit

At most a number of runs start per period. Events beyond that are skipped and never run. Rate limit in the Inngest docs.

Settings

Limit: 3Period: 10s

15 events, 11 runs, 4 skipped.started at oncedelayedskippedmerged into a later run

The numbers

Event arrives	Outcome	Its run starts
0s	started at once	0s
1s	started at once	1s
1.5s	started at once	1.5s
2s	skipped	never
3s	skipped	never
4s	started at once	4s
10s	started at once	10s
11s	started at once	11s
12s	skipped	never
13s	skipped	never
25s	started at once	25s
26s	started at once	26s
40s	started at once	40s
41s	started at once	41s
42s	started at once	42s

Debounce

One run starts once events stop arriving for a period, with the last event. A timeout caps the wait. Debounce in the Inngest docs.

Settings

Period: 5sTimeout (0 for none): 15s

15 events, 4 runs, 11 merged into a later event's run.started at oncedelayedskippedmerged into a later run

The numbers

Event arrives	Outcome	Its run starts
0s	merged into a later run	9s
1s	merged into a later run	9s
1.5s	merged into a later run	9s
2s	merged into a later run	9s
3s	merged into a later run	9s
4s	started at once	9s
10s	merged into a later run	18s
11s	merged into a later run	18s
12s	merged into a later run	18s
13s	started at once	18s
25s	merged into a later run	31s
26s	started at once	31s
40s	merged into a later run	47s
41s	merged into a later run	47s
42s	started at once	47s

Reading the timeline

Each dot on the top line is an event. Each bar below is a run, from when it starts to when it ends, and the line from an event leads to the run that handles it. A slanted line means the run started later than its event arrived.

The model is simple on purpose: one key, every run is a single step, and timings are in seconds. Inngest’s scheduler works with more detail, for example concurrency limits steps rather than whole runs, and rate limiting uses the generic cell rate algorithm with the period starting at the first event. Inngest has its own flow control simulator for exact behavior.

In code

Each of these is one attribute on the function class, or one property of FunctionOptions:

Attributes

[Concurrency(2)]
[Throttle(3, "10s", Burst = 1)]
[RateLimit(3, "10s")]

A debounce takes a period and an optional timeout:

[Debounce("5s", Timeout = "15s")]

Code first

Concurrency = [new ConcurrencyLimit(2)],
Throttle = new Throttle(3, TimeSpan.FromSeconds(10)) { Burst = 1 },
RateLimit = new RateLimit(3, TimeSpan.FromSeconds(10)),

A debounce takes a period and an optional timeout:

Debounce = new Debounce(TimeSpan.FromSeconds(5)) { Timeout = TimeSpan.FromSeconds(15) },

Flow control covers every option, including keys that give each customer a limit of its own.