Add histograms to measure DNS lookups for different configurations.

net/base/host_resolver_impl.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/base/host_resolver_impl.h"
 
 #if defined(OS_WIN)
 #include <Winsock2.h>
 #elif defined(OS_POSIX)
 #include <netdb.h>
@@ skipping 642 matching lines @@
 
     base::TimeDelta duration = base::TimeTicks::Now() - start_time;
     if (error == OK) {
       if (had_non_speculative_request_) {
         category = RESOLVE_SUCCESS;
         DNS_HISTOGRAM("DNS.ResolveSuccess", duration);
       } else {
         category = RESOLVE_SPECULATIVE_SUCCESS;
         DNS_HISTOGRAM("DNS.ResolveSpeculativeSuccess", duration);
       }
+
+      // Log DNS lookups based on address_family.  This will help us determine
+      // if IPv4 or IPv4/6 lookups are faster or slower.
+      switch(key_.address_family) {
+        case ADDRESS_FAMILY_IPV4:
+          DNS_HISTOGRAM("DNS.ResolveSuccess_FAMILY_IPV4", duration);
+          break;
+        case ADDRESS_FAMILY_IPV6:
+          DNS_HISTOGRAM("DNS.ResolveSuccess_FAMILY_IPV6", duration);
+          break;
+        case ADDRESS_FAMILY_UNSPECIFIED:
+          DNS_HISTOGRAM("DNS.ResolveSuccess_FAMILY_UNSPEC", duration);
+          break;

[jar (doing other things), 2011/06/09 18:30:00]

nit: perchance add a default: NOT_REACHED.

The style guide suggests this for non-enumerated cases, but also claims that in
enumerated cases the compiler will warn.... but I doubt our compiler provides
such a warning.

[cbentzel, 2011/06/09 18:47:03]

I've had compiler warnings for that case [I believe gcc on Linux does, perhaps
others]. 

+      }
     } else {
       if (had_non_speculative_request_) {
         category = RESOLVE_FAIL;
         DNS_HISTOGRAM("DNS.ResolveFail", duration);
       } else {
         category = RESOLVE_SPECULATIVE_FAIL;
         DNS_HISTOGRAM("DNS.ResolveSpeculativeFail", duration);
       }
+      // Log DNS lookups based on address_family.  This will help us determine
+      // if IPv4 or IPv4/6 lookups are faster or slower.
+      switch(key_.address_family) {
+        case ADDRESS_FAMILY_IPV4:
+          DNS_HISTOGRAM("DNS.ResolveFail_FAMILY_IPV4", duration);
+          break;
+        case ADDRESS_FAMILY_IPV6:
+          DNS_HISTOGRAM("DNS.ResolveFail_FAMILY_IPV6", duration);
+          break;
+        case ADDRESS_FAMILY_UNSPECIFIED:
+          DNS_HISTOGRAM("DNS.ResolveFail_FAMILY_UNSPEC", duration);
+          break;
+      }
       UMA_HISTOGRAM_CUSTOM_ENUMERATION(kOSErrorsForGetAddrinfoHistogramName,
                                        std::abs(os_error),
                                        GetAllGetAddrinfoOSErrors());
     }
     DCHECK_LT(category, static_cast<int>(RESOLVE_MAX));  // Be sure it was set.
 
     UMA_HISTOGRAM_ENUMERATION("DNS.ResolveCategory", category, RESOLVE_MAX);
 
     static const bool show_speculative_experiment_histograms =
         base::FieldTrialList::TrialExists("DnsImpact");
@@ skipping 924 matching lines @@
     additional_resolver_flags_ |= HOST_RESOLVER_LOOPBACK_ONLY;
   } else {
     additional_resolver_flags_ &= ~HOST_RESOLVER_LOOPBACK_ONLY;
   }
 #endif
   AbortAllInProgressJobs();
   // |this| may be deleted inside AbortAllInProgressJobs().
 }
 
 }  // namespace net