Write stage optimizations (#1534)

- Testnet dashboard shows that channel pressure for write stage
  is incrementing on every iteration of write.
- This change optimizes ledger writing by removing cloning of map
  and reducing calls to flush

src/ledger.rs

@@ -368,7 +368,7 @@ impl LedgerWriter {
         Ok(LedgerWriter { index, data })
     }
 
-    fn write_entry_noflush(&mut self, entry: &Entry) -> io::Result<()> {
+    pub fn write_entry_noflush(&mut self, entry: &Entry) -> io::Result<()> {
         let len = serialized_size(&entry).map_err(err_bincode_to_io)?;
 
         serialize_into(&mut self.data, &len).map_err(err_bincode_to_io)?;
@@ -395,23 +395,25 @@ impl LedgerWriter {
         Ok(())
     }
 
-    pub fn write_entry(&mut self, entry: &Entry) -> io::Result<()> {
-        self.write_entry_noflush(&entry)?;
+    pub fn flush(&mut self) -> io::Result<()> {
         self.index.flush()?;
         self.data.flush()?;
         Ok(())
     }
 
+    pub fn write_entry(&mut self, entry: &Entry) -> io::Result<()> {
+        self.write_entry_noflush(&entry)?;
+        self.flush()
+    }
+
     pub fn write_entries<I>(&mut self, entries: I) -> io::Result<()>
     where
         I: IntoIterator<Item = Entry>,
     {
         for entry in entries {
             self.write_entry_noflush(&entry)?;
         }
-        self.index.flush()?;
-        self.data.flush()?;
-        Ok(())
+        self.flush()
     }
 }
 

src/write_stage.rs

@@ -166,15 +166,15 @@ impl WriteStage {
 
         let start = Instant::now();
         for entries in ventries {
-            for e in &entries {
-                num_txs += e.transactions.len();
-            }
             let cluster_info_votes_start = Instant::now();
             let votes = &entries.votes();
             cluster_info.write().unwrap().insert_votes(&votes);
             cluster_info_votes_total += duration_as_ms(&cluster_info_votes_start.elapsed());
 
-            ledger_writer.write_entries(entries.clone())?;
+            for e in &entries {
+                num_txs += e.transactions.len();
+                ledger_writer.write_entry_noflush(&e)?;
+            }
             // Once the entries have been written to the ledger, then we can
             // safely incement entry height
             *entry_height += entries.len() as u64;
@@ -196,6 +196,7 @@ impl WriteStage {
 
             entries_send_total += duration_as_ms(&entries_send_start.elapsed());
         }
+        ledger_writer.flush()?;
         inc_new_counter_info!(
             "write_stage-time_ms",
             duration_as_ms(&now.elapsed()) as usize