And waits for them. That's pointless.
MergeTreeData::MutableDataPartPtr & new_data_part,
    const MergeTreeData::DataPartsVector & parts,
    MergeTreeData::Transaction * out_transaction)
{
    
    auto replaced_parts = data.renameTempPartAndReplace(new_data_part, nullptr, out_transaction);
    
    if (replaced_parts.size() != parts.size())
    {
        /** This is normal, although this happens rarely.
         *
         * The situation - was replaced 0 parts instead of N can be, for example, in the following case
         * - we had A part, but there was no B and C parts;
         * - A, B -> AB was in the queue, but it has not been done, because there is no B part;
         * - AB, C -> ABC was in the queue, but it has not been done, because there are no AB and C parts;
         * - we have completed the task of downloading a B part;
         * - we started to make A, B -> AB merge, since all parts appeared;
         * - we decided to download ABC part from another replica, since it was impossible to make merge AB, C -> ABC;
         * - ABC part appeared. When it was added, old A, B, C parts were deleted;
         * - AB merge finished. AB part was added. But this is an obsolete part. The log will contain the message `Obsolete part added`,
         *   then we get here.
         *
         * When M > N parts could be replaced?
         * - new block was added in ReplicatedMergeTreeBlockOutputStream;