Golang : How to get garbage collection data?

Problem :

You have read the previous tutorial on recovering memory and you want to trigger garbage collection manually with runtime/debug.FreeOSMemory() or calculate the percentage to use with runtime/debug.SetGCPercent() function, but you need to figure out what are the parameters to take into account and other information such as the last garbage collection time, available heap size, the number of garbage collection and etc.

Solution :

Use runtime.ReadMemStats() and runtime/debug.ReadGCStats() functions to gather the garbage collection data.

 package main

 import (
 "fmt"
 "runtime"
 "runtime/debug"
 )

 func main() {
 s := new(runtime.MemStats)
 runtime.ReadMemStats(s)

 fmt.Println("Alloc : ", s.Alloc)
 fmt.Println("Total Alloc : ", s.TotalAlloc)
 fmt.Println("Sys : ", s.Sys)
 fmt.Println("Lookups : ", s.Lookups)

 // Garbage Collection data
 fmt.Println("HeapAlloc : ", s.HeapAlloc)
 fmt.Println("Next Garbage Collection : ", s.NextGC)
 fmt.Println("Auto garbage collection will happen when HeapAlloc >= NextGC")
 fmt.Println("Last Garbage Collection : ", s.LastGC)
 fmt.Println("Total number of GC pause : ", s.PauseTotalNs)

 // [256]uint64 array
 // we will take the first element for this example...you might want to loop the array
 fmt.Println("Most recent pause : ", s.PauseNs[0])
 fmt.Println("Recent pause end times : ", s.PauseEnd[0])

 fmt.Println("Number of Garbage Collections : ", s.NumGC)
 fmt.Println("Is Garbage Collection enabled? : ", s.EnableGC)

 fmt.Println("Is Garbage Collection debug enabled? : ", s.DebugGC)

 // ---------------------------

 gcs := new(debug.GCStats)
 debug.ReadGCStats(gcs)

 fmt.Println("Last Garbage Collection : ", gcs.LastGC)

 fmt.Println("Number of Garbage Collection : ", gcs.NumGC)
 fmt.Println("Total pause for all collections : ", gcs.PauseTotal)

 // []time.Duration array
 fmt.Println("Most recent pause history : ", gcs.Pause)

 // []time.Time array
 fmt.Println("Most recent pause end times history : ", gcs.PauseEnd)

 // []time.Duration array
 // Pause Quantiles == values taken at regular interval
 fmt.Println("Most recent pause quantiles history : ", gcs.PauseQuantiles)
 }

References :

http://golang.org/pkg/runtime/debug/#FreeOSMemory

http://golang.org/pkg/runtime/debug/#ReadGCStats

http://golang.org/pkg/runtime/#ReadMemStats

http://golang.org/pkg/runtime/debug/#SetGCPercent