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

Some times there are not output from requests.
{
        auto old_header = old_metadata.getSampleBlock();
        performRequiredConversions(old_header, columns_to_check_conversion, getContext());
    }
    if (old_metadata.hasSettingsChanges())
    {
        const auto current_changes = old_metadata.getSettingsChanges()->as<const ASTSetQuery &>().changes;
        const auto & new_changes = new_metadata.settings_changes->as<const ASTSetQuery &>().changes;
        for (const auto & changed_setting : new_changes)
        {
            const auto & setting_name = changed_setting.name;
            const auto & new_value = changed_setting.value;
            MergeTreeSettings::checkCanSet(setting_name, new_value);
            const Field * current_value = current_changes.tryGet(setting_name);
            if ((!current_value || *current_value != new_value)
                && MergeTreeSettings::isReadonlySetting(setting_name))
            {
                throw Exception{"Setting '" + setting_name + "' is readonly for storage '" + getName() + "'",
                                 ErrorCodes::READONLY_SETTING};
            }
            if (!current_value && MergeTreeSettings::isPartFormatSetting(setting_name))
            {
                MergeTreeSettings copy = *getSettings();
                copy.applyChange(changed_setting);
                String reason;
                if (!canUsePolymorphicParts(copy, &reason) && !reason.empty())
                    throw Exception("Can't change settings. Reason: " + reason, ErrorCodes::NOT_IMPLEMENTED);
            }
            if (setting_name == "storage_policy")
                checkStoragePolicy(getContext()->getStoragePolicy(new_value.safeGet<String>()));