Memory in go
- 1. Memory in Go Jakarta, 16 November 2017 Meetup: GO-JEK and Go [email protected]
- 2. About Me ● 7++ year code experience at various language including java, ruby, go, c++, javascript, etc. ● 1++ year code in Go ● ~2 year on Gojek ● Fraud Engineer: working on fraud detection/prevention platform
- 3. Memory Management "The memory management on the PowerPC can be used to frighten small children." - Linus Torvalds
- 4. Address Space Stack Heap Program Text Free Memory 0x000000 0x7ffffff ● LIFO ● Last Allocate First Deallocate ● Cheaper and Faster ● Local variable and function parameter ● Free Store ● Free to allocate/deallocate ● Long life variable Literally your code
- 5. A variable allocated on the heap or the stack? ● You don't need to know; it’s handle by compiler. ● When possible, variable will be allocate on the stack ● If variable is very large, allocate on the heap ● If variable is still referenced after the function returns, allocate to heap. ● Escape Analysis is a method to check whether variable escape to another initial scope.
- 6. Escape Analysis Because localVar still referenced after end of function
- 7. Pointers “My address is like my shoes. It travel with me” - Mary Harris Jones
- 9. Operator & Pointer is Data Type Address of value Nil Pointers is pointer that no referencing any value
- 10. Operator * Value of pointer This is known as "dereferencing" or "indirecting"
- 11. Pointers and Function Everything in Go is passed by value. Function always gets a copy of the thing being passed
- 12. Slice/Map Map and slice values behave like pointers
- 13. Pointer Receiver For big struct because cheaper For basic type, slice, or small struct because efficient and clean Not modify field on MyStruct Be consistent
- 14. Garbage Collector “C programmers think memory management is too important to be left to the computer. Lisp programmers think memory management is too important to be left to the user.” - Bjarne Stroustrup “Go is building a garbage collector (GC) not only for 2015 but for 2025” - Richard Hudson
- 15. GC on General ● Garbage = memory occupied by objects that are no longer in use ● Mark - Sweep: ○ Mark – identifies which pieces of memory are in use and which are not ○ Sweep – removes objects identified during the “mark” phase ● GC Strategy: ○ Stop The World - completely halt execution of the program ○ Incremental - perform in discrete phases, with program execution permitted between each phase ○ Concurrent - do not stop program execution at all, except perhaps briefly when the program's execution stack is scanned
- 16. Why Go GC can probably better than Java? Go Java Thousands of Goroutines Tens of Java Threads Synchronization via channels Synchronization via objects/locks Runtime written in Go Runtime written in C Control of spatial locality; Objects can be embedded Interior pointers (&foo.field) Objects linked with pointers
- 17. GC on Go ● Prioritizing low latency and simplicity ● Concurrent, tri-color, mark-sweep collector
- 18. GC Latency on Go ● 300 ms (Go 1.4) ● 40 ms (Go 1.5) ● 3 ms (Go 1.6) ● ~1 ms (Go 1.7) ● < 100 μs (Go 1.8) ● < 100 μs even for very large heap (Go 1.9)
- 19. GC Optimization ● GOGC Variable = the ratio of freshly allocated data to live data remaining after the previous collection reaches (percentage) ● The default is 100, mean triggered when total heap size is now 100% bigger than (i.e., twice) the size of the reachable objects after the last collection ● If you want to lower the total time spent in GC, increase GOGC. ● If you want to trade more GC time for less memory, lower GOGC. ● GOGC=off disables the garbage collector entirely. ● You may trigger a garbage collection "manually" with runtime.GC().
- 20. Never Stop Learning ● https://golang.org/doc/faq ● https://talks.golang.org/2015/go-gc.pdf ● https://dave.cheney.net/2014/06/07/five-things-that-make-go-fast ● https://making.pusher.com/golangs-real-time-gc-in-theory-and-practice/ ● https://dougrichardson.org/2016/01/23/go-memory-allocations.html
- 21. QUESTION? We are hiring! Contact [email protected] Shortcut contact: [email protected] [email protected]