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

Some times there are not output from requests.
{
    std::lock_guard lock(query_id_set_mutex);
    removeQueryIdNoLock(query_id);
}
void MergeTreeData::removeQueryIdNoLock(const String & query_id) const
{
    if (query_id_set.find(query_id) == query_id_set.end())
        LOG_WARNING(log, "We have query_id removed but it's not recorded. This is a bug");
    else
        query_id_set.erase(query_id);
}
ReservationPtr MergeTreeData::balancedReservation(
    const StorageMetadataPtr & metadata_snapshot,
    size_t part_size,
    size_t max_volume_index,
    const String & part_name,
    const MergeTreePartInfo & part_info,
    MergeTreeData::DataPartsVector covered_parts,
    std::optional<CurrentlySubmergingEmergingTagger> * tagger_ptr,
    const IMergeTreeDataPart::TTLInfos * ttl_infos,
    bool is_insert)