Go by Example: Rate Limiting
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Rate limiting is an important mechanism for controlling resource utilization and maintaining quality of service. Go elegantly supports rate limiting with goroutines, channels, and tickers. |
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package main
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import "time"
import "fmt"
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func main() {
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First we’ll look at basic rate limiting. Suppose we want to limit our handling of incoming requests. We’ll serve these requests off a channel of the same name. |
requests := make(chan int, 5)
for i := 1; i <= 5; i++ {
requests <- i
}
close(requests)
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This |
limiter := time.Tick(time.Millisecond * 200)
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By blocking on a receive from the |
for req := range requests {
<-limiter
fmt.Println("request", req, time.Now())
}
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We may want to allow short bursts of requests in
our rate limiting scheme while preserving the
overall rate limit. We can accomplish this by
buffering our limiter channel. This |
burstyLimiter := make(chan time.Time, 3)
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Fill up the channel to represent allowed bursting. |
for i := 0; i < 3; i++ {
burstyLimiter <- time.Now()
}
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Every 200 milliseconds we’ll try to add a new
value to |
go func() {
for t := range time.Tick(time.Millisecond * 200) {
burstyLimiter <- t
}
}()
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Now simulate 5 more incoming requests. The first
3 of these will benefit from the burst capability
of |
burstyRequests := make(chan int, 5)
for i := 1; i <= 5; i++ {
burstyRequests <- i
}
close(burstyRequests)
for req := range burstyRequests {
<-burstyLimiter
fmt.Println("request", req, time.Now())
}
}
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Running our program we see the first batch of requests handled once every ~200 milliseconds as desired. |
$ go run rate-limiting.go
request 1 2012-10-19 00:38:18.687438 +0000 UTC
request 2 2012-10-19 00:38:18.887471 +0000 UTC
request 3 2012-10-19 00:38:19.087238 +0000 UTC
request 4 2012-10-19 00:38:19.287338 +0000 UTC
request 5 2012-10-19 00:38:19.487331 +0000 UTC
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For the second batch of requests we serve the first 3 immediately because of the burstable rate limiting, then serve the remaining 2 with ~200ms delays each. |
request 1 2012-10-19 00:38:20.487578 +0000 UTC
request 2 2012-10-19 00:38:20.487645 +0000 UTC
request 3 2012-10-19 00:38:20.487676 +0000 UTC
request 4 2012-10-19 00:38:20.687483 +0000 UTC
request 5 2012-10-19 00:38:20.887542 +0000 UTC
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Previous example: Worker Pools.
Next example: Atomic Counters.