Statistics
https://play.clickhouse.com/play?user=play#c2VsZWN0IAp0b1N0YXJ0T2ZIb3VyKGNoZWNrX3N0YXJ0X3RpbWUpIGFzIGQsCmNvdW50KCksICBncm91cFVuaXFBcnJheShwdWxsX3JlcXVlc3RfbnVtYmVyKSwgIGFueShyZXBvcnRfdXJsKQpmcm9tIGNoZWNrcyB3aGVyZSAnMjAyMi0wNi0wMScgPD0gY2hlY2tfc3RhcnRfdGltZSBhbmQgdGVzdF9uYW1lIGxpa2UgJyUwMjQ5MV9wYXJ0X2xvZ19oYXNfdGFibGVfdXVpZCUnIGFuZCB0ZXN0X3N0YXR1cyBpbiAoJ0ZBSUwnLCAnRkxBS1knKSBncm91cCBieSBkIG9yZGVyIGJ5IGQgZGVzYw==

Some times there are not output from requests.
{
    if (getSettings()->in_memory_parts_enable_wal)
        return;
    auto metadata_snapshot = getInMemoryMetadataPtr();
    DataPartsVector parts = getDataPartsVectorForInternalUsage();
    for (const auto & part : parts)
    {
        if (auto part_in_memory = asInMemoryPart(part))
        {
            part_in_memory->flushToDisk(part_in_memory->getDataPartStorage().getPartDirectory(), metadata_snapshot);
        }
    }
}
size_t MergeTreeData::clearOldPartsFromFilesystem(bool force)
{
    DataPartsVector parts_to_remove = grabOldParts(force);
    clearPartsFromFilesystem(parts_to_remove);
    removePartsFinally(parts_to_remove);
    
    
    if (!parts_to_remove.empty())
        getContext()->dropMMappedFileCache();
    return parts_to_remove.size();
}
void MergeTreeData::clearPartsFromFilesystem(const DataPartsVector & parts, bool throw_on_error, NameSet * parts_failed_to_delete)