Don't keep too much LOG.old.* files

src/store.rs

@@ -44,6 +44,7 @@ impl DBStore {
         let mut db_opts = rocksdb::DBOptions::default();
         db_opts.create_if_missing(true);
         db_opts.increase_parallelism(2);
+        db_opts.set_keep_log_file_num(10);
 
         let mut cf_opts = rocksdb::rocksdb_options::ColumnFamilyOptions::new();
         cf_opts.set_compaction_style(rocksdb::DBCompactionStyle::Level);