What kind of Garbage Collection does Go use?

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Plans for Go 1.4+ garbage collector:

  • hybrid stop-the-world/concurrent collector
  • stop-the-world part limited by a 10ms deadline
  • CPU cores dedicated to running the concurrent collector
  • tri-color mark-and-sweep algorithm
  • non-generational
  • non-compacting
  • fully precise
  • incurs a small cost if the program is moving pointers around
  • lower latency, but most likely also lower throughput, than Go 1.3 GC

Go 1.3 garbage collector updates on top of Go 1.1:

  • concurrent sweep (results in smaller pause times)
  • fully precise

Go 1.1 garbage collector:

  • mark-and-sweep (parallel implementation)
  • non-generational
  • non-compacting
  • mostly precise (except stack frames)
  • stop-the-world
  • bitmap-based representation
  • zero-cost when the program is not allocating memory (that is: shuffling pointers around is as fast as in C, although in practice this runs somewhat slower than C because the Go compiler is not as advanced as C compilers such as GCC)
  • supports finalizers on objects
  • there is no support for weak references

Go 1.0 garbage collector:

  • same as Go 1.1, but instead of being mostly precise the garbage collector is conservative. The conservative GC is able to ignore objects such as []byte.

Replacing the GC with a different one is controversial, for example:

  • except for very large heaps, it is unclear whether a generational GC would be faster overall
  • package “unsafe” makes it hard to implement fully precise GC and compacting GC

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