Slides for the talk given by Bryan Boreham at DotGoEU 2019.

1. Tune Your Garbage-Collector!
@bboreham

2. Stack vs Heap
2http://www.clipartpanda.com/clipart_images/stack-files-max-39545601 Photo: JohnNyberg, rgbstock.com

3. GC Tuning Options
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-Xmsn
-Xmxn
-XX:-UseConcMarkSweepGC
-XX:-UseParallelGC
-XX:-UseParallelOldGC
-XX:-UseSerialGC
-XX:+UseG1GC
-XX:+UseGCOverheadLimit
-XX:MaxGCPauseMillis=n
-XX:InitiatingHeapOccupancyPercent
-XX:MaxTenuringThreshold=n
-XX:+ScavengeBeforeFullGC
-XX:ParallelGCThreads=n
-XX:ConcGCThreads=n
-XX:G1ReservePercent=n
-XX:G1HeapRegionSize=n
-XX:MaxHeapFreeRatio=n
-XX:MaxNewSize=size
-XX:MaxPermSize=n
-XX:MinHeapFreeRatio=n
-XX:NewSize=n
-XX:NewRatio=n
-XX:SurvivorRatio=n
-XX:TargetSurvivorRatio=n
-XX:+HandlePromotionFailure

4. GOGC
Go GC Options
4

5. The Go heap.
5

6. Allocate some more memory
6

7. Garbage-Collect!
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8. Allocate more memory
8

9. Garbage collect!
9

10. Allocate much more memory!
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11. Garbage collect!
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12. Allocate!
12

13. Garbage collect!
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14. Chart it!
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Growth
before
next GC
Heap size
after GC

15. GOGC
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100%
Heap size
after GC

16. Situation: large stable data set
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GOGC=50
20 GBytes

17. Situation: small heap, very rapid GC
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GOGC=400
10 MBytes

18. GOGC=off
What if we turn off GC completely?
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19. GOGC=off go build ./...
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Normal
7.3 seconds
5.3 seconds
GOGC=off

20. Try it out!
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Situation Action + -
Large static
data set
GOGC ➡ Smaller heap More CPU
Tiny heap,
rapid GC
GOGC Lower latency More RAM
One-shot
execution
GOGC=off Runs faster May explode

21. THANK YOU!
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@bboreham

22. More information
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Good explanation of GOGC and other settings
https://dave.cheney.net/tag/gogc
Really detailed history https://blog.golang.org/ismmkeynote