fix: ensure WAL is atomic for each write batch (#84)

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm/src/mem_table.rs

@@ -91,6 +91,7 @@ impl MemTable {
     ///
     /// In week 1, day 1, simply put the key-value pair into the skipmap.
     /// In week 2, day 6, also flush the data to WAL.
+    /// In week 3, day 5, modify the function to use the batch API.
     pub fn put(&self, key: &[u8], value: &[u8]) -> Result<()> {
         let estimated_size = key.len() + value.len();
         self.map
@@ -103,6 +104,11 @@ impl MemTable {
         Ok(())
     }
 
+    /// Implement this in week 3, day 5.
+    pub fn put_batch(&self, _data: &[(KeySlice, &[u8])]) -> Result<()> {
+        unimplemented!()
+    }
+
     pub fn sync_wal(&self) -> Result<()> {
         if let Some(ref wal) = self.wal {
             wal.sync()?;

mini-lsm/src/wal.rs

@@ -79,6 +79,11 @@ impl Wal {
         Ok(())
     }
 
+    /// Implement this in week 3, day 5.
+    pub fn put_batch(&self, _data: &[(&[u8], &[u8])]) -> Result<()> {
+        unimplemented!()
+    }
+
     pub fn sync(&self) -> Result<()> {
         let mut file = self.file.lock();
         file.flush()?;