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

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

mini-lsm-starter/src/mem_table.rs

@@ -76,10 +76,16 @@ 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<()> {
         unimplemented!()
     }
 
+    /// 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-starter/src/wal.rs

@@ -27,6 +27,11 @@ impl Wal {
         unimplemented!()
     }
 
+    /// Implement this in week 3, day 5.
+    pub fn put_batch(&self, _data: &[(&[u8], &[u8])]) -> Result<()> {
+        unimplemented!()
+    }
+
     pub fn sync(&self) -> Result<()> {
         unimplemented!()
     }