Агрегация группы серверов DNS
Если SQL Server будет думать, что будет менее дорого использовать некластерный индекс при поиске крайнего левого столбца затем, это будет. Проблема в Вашем случае (я предполагаю) состоит в том, что Вы делаете ВЫБОР * вместо того, чтобы указать только столбцы, которые Вы хотите назад. При определении столбцов, которые не являются в некластерном индексе затем, SQL Server должен будет сделать ключевой поиск после того, как индекс будет искать и возвращается к кластерному индексу (или "куча", если нет никакого кластерного индекса) получить остальную часть столбцов.
Если Вам только нужны несколько столбцов, тогда указывают их и добавляют их как включенные столбцы в существующем индексе, и SQL Server начнет использовать индекс.
This sounds like a job for dnsmasq ( http://www.thekelleys.org.uk/dnsmasq/doc.html ) which makes it easy to define authoritative servers for different domains. For example, if example1.com DNS is on 192.168.1.2 you could tell dnsmasq --server=/example2.com/192.168.1.2.
dnsmasq provides various methods for aliasing addresses - it can convert internal addresses into external addresses (which I don't think is likely needed here). It can act as a general resolver, or just as an authoritative server. And, you can bind it to various interfaces or ports. For example, we use dnsmasq on port 53 as a front end to our internal bind/named servers on 5353 to do various inserttions and translations.
dnsmasq is used in many firewalls and gateways, and is (one might say) the DNS Swiss army knife.
You could probably set up your DNS server to use conditional forwarders, pointing at the other DNS servers, for the domains you want it to resolve. This is not completely transparent, but it will pass the queries through and the results back.
Otherwise, you would have to configure a load balancer to inspect the queries and send them to the right server. I don't know of any load balancer which would support this, though you could construct one with iptables and layer 7 filtering, using DNAT to redirect the queries and SNAT to "proxy" them.
Assuming Unix/Linux boxes (Windows should be similar):
- In the world-facing DNS server, include only the information that you want the outside world to see.
- The gateway machine should use the internal DNS servers for resolving (i.e., put the internal DNS servers in /etc/resolv.conf).
- The internal DNS servers should use the gateway machine in their "forwarders" statement.
It would be better if the world-facing DNS server was not also your gateway as you're risking exposure of your internal DNS data. Why not host your external zone elsewhere, such as at your service provider? If you can move the world-facing DNS server to a different box (or even a different network), the DNS server on the gateway should only listen on port 53 on the internal NIC.