main: Limit garbage collection percentage. (#686)

This reduces the target ratio of freshly allocated data to live data to
10% in order to limit excessive overallocations by the garbage collector
during data bursts such as processing complex blocks or rapidly
receiving a lot of large transactions.

btcd.go

@@ -11,6 +11,7 @@ import (
 	_ "net/http/pprof"
 	"os"
 	"runtime"
+	"runtime/debug"
 	"runtime/pprof"
 
 	"github.com/btcsuite/btcd/blockchain/indexers"
@@ -150,6 +151,12 @@ func main() {
 	// Use all processor cores.
 	runtime.GOMAXPROCS(runtime.NumCPU())
 
+	// Block and transaction processing can cause bursty allocations.  This
+	// limits the garbage collector from excessively overallocating during
+	// bursts.  This value was arrived at with the help of profiling live
+	// usage.
+	debug.SetGCPercent(10)
+
 	// Up some limits.
 	if err := limits.SetLimits(); err != nil {
 		fmt.Fprintf(os.Stderr, "failed to set limits: %v\n", err)