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I am building a test crawler and wanted to know if Go (golang) caches DNS queries. I don't see anything about caching in the dnsclient. This seems like an important thing to add to any crawler to prevent lots of extra DNS queries.
Does Go (1.4+) cache DNS lookups?
If not, does debian/ubuntu/linux, windows, or darwin/OSX do any caching at the network level Go benefits from?
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The DNS cache is a local storage of DNS records maintained by the operating system. The DNS cache contains the Resource Records (RR) of the domains you have previously visited and their IP address translations. When you access a web page, your computer's OS initiates a DNS lookup for the domain.
Windows: Open your command prompt and enter the command “ipconfig /displaydns.” You should then be able to see the records. Mac: Open the Terminal app, enter the command “sudo discoveryutil udnscachestats,” and input your password. This will display the Unicast DNS cache.
DNS cache, as discussed, is not only cached by an operating system like Windows; the browser you're using may also be caching DNS records. We have the option to clear the same. For Chrome, open a new tab and enter chrome://net-internals/#dns in the address bar and press Enter .
A DNS cache (sometimes called a DNS resolver cache) is a temporary database, maintained by a computer's operating system, that contains records of all the recent visits and attempted visits to websites and other internet domains.
To display the contents of the DNS cache, you need to execute the following command in an elevated Command Prompt: 1 Press the Win + S shortcut key ... 2 Click on Run as administrator on the right pane. 3 On the Command Prompt window, type the following command and press Enter: ipconfig /displaydns
Modern web browsers are designed by default to cache DNS records for a set quantity of time. The function here is obvious; the more detailed the DNS caching in the web internet browser, the fewer processing steps must be taken to inspect the cache and make the appropriate requests to an IP address.
Since clearing the DNS cache removes all the entries, it deletes any invalid records too and forces your computer to repopulate those addresses the next time you try accessing those websites. These new addresses are taken from the DNS server your network is set up to use.
Domain Name System information can be cached in a variety of locations, each of which will store DNS records for a set amount of time determined by a time-to-live (TTL). Modern web browsers are designed by default to cache DNS records for a set quantity of time.
The answer to your question is no. There is no built-in dns caching in the std lib resolver. Would it be helpful? Maybe in some cases. Our org runs a local dns cache on each server and points resolv.conf there. So it wouldn't necessarily help us much to have caching in the language.
There are some solutions that could help you. This package seems to have a pretty good solution. From the snippet in their readme you could even do:
http.DefaultClient.Transport = &http.Transport {
MaxIdleConnsPerHost: 64,
Dial: func(network string, address string) (net.Conn, error) {
separator := strings.LastIndex(address, ":")
ip, _ := dnscache.FetchString(address[:separator])
return net.Dial("tcp", ip + address[separator:])
},
}
To enable it for all http requests from http.Get and friends.
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