*: add an option to disable write-ahead-log.

src/rocksdb.rs

@@ -434,6 +434,12 @@ impl DB {
         self.write_opt(batch, &WriteOptions::default())
     }
 
+    pub fn write_withou_wal(&self, batch: WriteBatch) -> Result<(), String> {
+        let mut wo = WriteOptions::new();
+        wo.disable_wal(true);
+        self.write_opt(batch, &wo)
+    }
+
     pub fn get_opt(&self,
                    key: &[u8],
                    readopts: &ReadOptions)

src/rocksdb_options.rs

@@ -334,11 +334,22 @@ impl WriteOptions {
     pub fn new() -> WriteOptions {
         WriteOptions::default()
     }
+
     pub fn set_sync(&mut self, sync: bool) {
         unsafe {
             rocksdb_ffi::rocksdb_writeoptions_set_sync(self.inner, sync);
         }
     }
+
+    pub fn disable_wal(&mut self, disable: bool) {
+        unsafe {
+            if disable {
+                rocksdb_ffi::rocksdb_writeoptions_disable_WAL(self.inner, 1);
+            } else {
+                rocksdb_ffi::rocksdb_writeoptions_disable_WAL(self.inner, 0);
+            }
+        }
+    }
 }
 
 impl Default for WriteOptions {