diff --git a/src/main.rs b/src/main.rs
index 7eeab3e..b8ec2df 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -246,12 +246,12 @@ impl From<&SourceQuestionsBatch> for BatchInfo {
     }
 }
 
-impl Into<Vec<Question>> for SourceQuestionsBatch {
-    fn into(self) -> Vec<Question> {
-        let mut result = Vec::<Question>::with_capacity(self.questions.len());
-        self.questions.iter().for_each(|item| {
+impl From<SourceQuestionsBatch> for Vec<Question> {
+    fn from(src: SourceQuestionsBatch) -> Self {
+        let mut result = Vec::<Question>::with_capacity(src.questions.len());
+        src.questions.iter().for_each(|item| {
             let mut question: Question = item.clone().into();
-            question.batch_info = BatchInfo::from(&self);
+            question.batch_info = BatchInfo::from(&src);
             result.push(question);
         });
 
@@ -264,7 +264,7 @@ pub fn measure<F: FnOnce()>(func: F) -> f64 {
     let start = Instant::now();
     func();
     let elapsed = start.elapsed();
-    (elapsed.as_secs() as f64) + (elapsed.subsec_nanos() as f64 / 1000_000_000.0)
+    (elapsed.as_secs() as f64) + (elapsed.subsec_nanos() as f64 / 1_000_000_000.0)
 }
 
 pub fn measure_and_print<F: FnOnce()>(func: F) {
@@ -308,19 +308,18 @@ fn writer_v4() {
             (String::from(name_str), data)
         })
         .filter(|(_, data)| data.is_ok())
-        .map(|(filename, data)| {
+        .flat_map(|(filename, data)| {
             let mut data = data.unwrap();
-            data.filename = filename.clone();
+            data.filename = filename;
             let questions: Vec<Question> = data.into();
             questions
         })
-        .flatten()
         .for_each(|question| {
             let result = collection.insert(&question);
             if result.is_err() {
                 println!(
                     "Error: {:?} \n\
-                         On: {:?}",
+                     On: {:?}",
                     result, question
                 );
             } else {
@@ -329,6 +328,11 @@ fn writer_v4() {
         });
 
     println!("inserted {}", count);
+    storage.sync(true).unwrap();
+    print!("stats: ");
+    let stats = storage.stat().unwrap();
+    println!("{:?}", stats);
+    drop(storage);
 }
 
 fn print_question(q: Question) {
@@ -347,13 +351,7 @@ fn reader_v1() -> Option<Question> {
     let data = data.unwrap();
     let questions: Vec<Question> = data.into();
 
-    let ret = questions.iter().choose(&mut rng);
-
-    if let Some(question) = ret {
-        Some(question.clone())
-    } else {
-        None
-    }
+    questions.into_iter().choose(&mut rng)
 }
 
 fn compact_db() {
@@ -367,13 +365,11 @@ fn compact_db() {
     .unwrap();
 
     let storage = Storage::new("db", options).unwrap();
-    //let collection = storage.collection("questions").unwrap();
 
-    //query!(index for collection
-    //    num int,
-    //    batch_info.filename str,
-    //)
-    //.unwrap();
+    storage.sync(true).unwrap();
+    let stats = storage.stat().unwrap();
+    println!("{:?}", stats);
+    drop(storage);
 }
 
 fn reader_v4() -> Option<Question> {