update comments

src/lib/homestore_backend/hs_shard_manager.cpp

@@ -180,8 +180,9 @@ bool HSHomeObject::do_shard_message_pre_commit(int64_t lsn, ReplicationMessageHe
     switch (header.msg_type) {
     case ReplicationMessageType::SEAL_SHARD_MSG: {
         // we can not release chunk here, since if rollback happens, we can not make sure we can get the same chunk.
-        // it might be selected by other creat_shard after we release it.
-        // we need to wait for the commit phase to release chunk;
+        // chunk selector will always return the a chunk of least used, and GC will happen at the time window
+        // we can not make sure we can get the same chunk as before, so we need to wait for the commit phase to release
+        // chunk;
         update_shard_in_map(shard_info);
         if (ctx) { ctx->promise_.setValue(ShardManager::Result< ShardInfo >(shard_info)); }
         break;