[#373] metabase: Add metrics

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/local_object_storage/metabase/exists.go

@@ -3,6 +3,7 @@ package meta
 import (
 	"context"
 	"fmt"
+	"time"
 
 	objectV2 "git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/object"
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/internal/metaerr"
@@ -45,6 +46,14 @@ func (p ExistsRes) Exists() bool {
 // Returns an error of type apistatus.ObjectAlreadyRemoved if object has been placed in graveyard.
 // Returns the object.ErrObjectIsExpired if the object is presented but already expired.
 func (db *DB) Exists(ctx context.Context, prm ExistsPrm) (res ExistsRes, err error) {
+	var (
+		startedAt = time.Now()
+		success   = false
+	)
+	defer func() {
+		db.metrics.AddMethodDuration("Exists", time.Since(startedAt), success)
+	}()
+
 	_, span := tracing.StartSpanFromContext(ctx, "metabase.Exists",
 		trace.WithAttributes(
 			attribute.String("address", prm.addr.EncodeToString()),
@@ -65,7 +74,7 @@ func (db *DB) Exists(ctx context.Context, prm ExistsPrm) (res ExistsRes, err err
 
 		return err
 	})
-
+	success = err == nil
 	return res, metaerr.Wrap(err)
 }