Add RocksDB options for in memory configurations.

When you set the path to rocksdb directory in memory like in /dev/shm,
you need to set the wal_dir and WAL_ttl_seconds options if you want to
recover your in-memory RocksDB database after a machine reboot.

See: https://github.com/facebook/rocksdb/wiki/How-to-persist-in-memory-RocksDB-database

librocksdb_sys/src/lib.rs

@@ -263,6 +263,9 @@ extern "C" {
     pub fn crocksdb_options_set_stats_dump_period_sec(options: *mut DBOptions, v: usize);
     pub fn crocksdb_options_set_num_levels(options: *mut DBOptions, v: c_int);
     pub fn crocksdb_options_set_db_log_dir(options: *mut DBOptions, path: *const c_char);
+    pub fn crocksdb_options_set_wal_dir(options: *mut DBOptions, path: *const c_char);
+    pub fn crocksdb_options_set_WAL_ttl_seconds(options: *mut DBOptions, ttl: u64);
+    pub fn crocksdb_options_set_WAL_size_limit_MB(options: *mut DBOptions, limit: u64);
     pub fn crocksdb_options_set_prefix_extractor(options: *mut DBOptions,
                                                  prefix_extractor: *mut DBSliceTransform);
     pub fn crocksdb_options_set_memtable_insert_with_hint_prefix_extractor(options: *mut DBOptions,

src/rocksdb_options.rs

@@ -654,6 +654,25 @@ impl Options {
         }
     }
 
+    pub fn set_wal_dir(&mut self, path: &str) {
+        let path = CString::new(path.as_bytes()).unwrap();
+        unsafe {
+            crocksdb_ffi::crocksdb_options_set_wal_dir(self.inner, path.as_ptr());
+        }
+    }
+
+    pub fn set_wal_ttl_seconds(&mut self, ttl: u64) {
+        unsafe {
+            crocksdb_ffi::crocksdb_options_set_WAL_ttl_seconds(self.inner, ttl as u64);
+        }
+    }
+
+    pub fn set_wal_size_limit_mb(&mut self, limit: u64) {
+        unsafe {
+            crocksdb_ffi::crocksdb_options_set_WAL_size_limit_MB(self.inner, limit as u64);
+        }
+    }
+
     pub fn set_max_log_file_size(&mut self, size: u64) {
         unsafe {
             crocksdb_ffi::crocksdb_options_set_max_log_file_size(self.inner, size as size_t);