Record size of snapshot persist

snapshot/snapshot.go

@@ -1,6 +1,7 @@
 package snapshot
 
 import (
+	"expvar"
 	"fmt"
 	"io"
 	"os"
@@ -38,7 +39,8 @@ func (s *Snapshot) Persist(sink raft.SnapshotSink) error {
 	}
 	defer stream.Close()
 
-	_, err = io.Copy(sink, stream)
+	n, err := io.Copy(sink, stream)
+	stats.Get(persistSize).(*expvar.Int).Set(n)
 	return err
 }
 

snapshot/store.go

@@ -3,6 +3,7 @@ package snapshot
 import (
 	"encoding/json"
 	"errors"
+	"expvar"
 	"fmt"
 	"io"
 	"log"
@@ -19,6 +20,11 @@ import (
 	"github.com/rqlite/rqlite/db"
 )
 
+func init() {
+	stats = expvar.NewMap("snapshot")
+	ResetStats()
+}
+
 const (
 	minSnapshotRetain = 2
 
@@ -32,6 +38,10 @@ const (
 	tmpSuffix         = ".tmp"
 )
 
+const (
+	persistSize = "persist_size"
+)
+
 var (
 	// ErrRetainCountTooLow is returned when the retain count is too low.
 	ErrRetainCountTooLow = errors.New("retain count must be >= 2")
@@ -43,6 +53,15 @@ var (
 	ErrSnapshotBaseMissing = errors.New("snapshot base SQLite file missing")
 )
 
+// stats captures stats for the Store.
+var stats *expvar.Map
+
+// ResetStats resets the expvar stats for this module. Mostly for test purposes.
+func ResetStats() {
+	stats.Init()
+	stats.Add(persistSize, 0)
+}
+
 // Meta represents the metadata for a snapshot.
 type Meta struct {
 	raft.SnapshotMeta