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      1 // Copyright 2014 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "chrome/common/variations/uniformity_field_trials.h"
      6 
      7 #include <string>
      8 
      9 #include "base/metrics/field_trial.h"
     10 #include "base/strings/stringprintf.h"
     11 #include "base/time/time.h"
     12 #include "components/variations/variations_associated_data.h"
     13 
     14 namespace chrome_variations {
     15 
     16 namespace {
     17 
     18 const int MINIMIUM_ID = 3300000;
     19 
     20 const int UNIFORMITY_1_PERCENT_BASE  = MINIMIUM_ID;
     21 const int UNIFORMITY_1_PERCENT_LIMIT = UNIFORMITY_1_PERCENT_BASE + 100;
     22 const int UNIFORMITY_5_PERCENT_BASE  = UNIFORMITY_1_PERCENT_LIMIT;
     23 const int UNIFORMITY_5_PERCENT_LIMIT = UNIFORMITY_5_PERCENT_BASE + 20;
     24 const int UNIFORMITY_10_PERCENT_BASE  = UNIFORMITY_5_PERCENT_LIMIT;
     25 const int UNIFORMITY_10_PERCENT_LIMIT = UNIFORMITY_10_PERCENT_BASE + 10;
     26 const int UNIFORMITY_20_PERCENT_BASE  = UNIFORMITY_10_PERCENT_LIMIT;
     27 const int UNIFORMITY_20_PERCENT_LIMIT = UNIFORMITY_20_PERCENT_BASE + 5;
     28 const int UNIFORMITY_50_PERCENT_BASE  = UNIFORMITY_20_PERCENT_LIMIT;
     29 // A uniformity trial used to compare one-time-randomized and
     30 // session-randomized FieldTrials.
     31 const int UNIFORMITY_SESSION_RANDOMIZED_5_PERCENT_BASE  = 3300139;
     32 
     33 // Set up a uniformity field trial. |one_time_randomized| indicates if the
     34 // field trial is one-time randomized or session-randomized. |trial_name_string|
     35 // must contain a "%d" since the percentage of the group will be inserted in
     36 // the trial name. |num_trial_groups| must be a divisor of 100 (e.g. 5, 20)
     37 void SetupSingleUniformityFieldTrial(
     38     base::FieldTrial::RandomizationType randomization_type,
     39     const std::string& trial_name_string,
     40     const variations::VariationID trial_base_id,
     41     int num_trial_groups) {
     42   // Probability per group remains constant for all uniformity trials, what
     43   // changes is the probability divisor.
     44   static const base::FieldTrial::Probability kProbabilityPerGroup = 1;
     45   const std::string kDefaultGroupName = "default";
     46   const base::FieldTrial::Probability divisor = num_trial_groups;
     47 
     48   DCHECK_EQ(100 % num_trial_groups, 0);
     49   const int group_percent = 100 / num_trial_groups;
     50   const std::string trial_name = base::StringPrintf(trial_name_string.c_str(),
     51                                                     group_percent);
     52 
     53   DVLOG(1) << "Trial name = " << trial_name;
     54 
     55   scoped_refptr<base::FieldTrial> trial(
     56       base::FieldTrialList::FactoryGetFieldTrial(
     57           trial_name, divisor, kDefaultGroupName, 2015, 1, 1,
     58           randomization_type, NULL));
     59   variations::AssociateGoogleVariationID(variations::GOOGLE_UPDATE_SERVICE,
     60                                          trial_name, kDefaultGroupName,
     61                                          trial_base_id);
     62 
     63   // Loop starts with group 1 because the field trial automatically creates a
     64   // default group, which would be group 0.
     65   for (int group_number = 1; group_number < num_trial_groups; ++group_number) {
     66     const std::string group_name =
     67           base::StringPrintf("group_%02d", group_number);
     68     DVLOG(1) << "    Group name = " << group_name;
     69     trial->AppendGroup(group_name, kProbabilityPerGroup);
     70     variations::AssociateGoogleVariationID(
     71         variations::GOOGLE_UPDATE_SERVICE, trial_name, group_name,
     72         static_cast<variations::VariationID>(trial_base_id + group_number));
     73   }
     74 
     75   // Now that all groups have been appended, call group() on the trial to
     76   // ensure that our trial is registered. This resolves an off-by-one issue
     77   // where the default group never gets chosen if we don't "use" the trial.
     78   const int chosen_group = trial->group();
     79   DVLOG(1) << "Chosen Group: " << chosen_group;
     80 }
     81 
     82 // Setup a 50% uniformity trial for new installs only. This is accomplished by
     83 // disabling the trial on clients that were installed before a specified date.
     84 void SetupNewInstallUniformityTrial(const base::Time install_date) {
     85   const base::Time::Exploded kStartDate = {
     86     2012, 11, 0, 6,  // Nov 6, 2012
     87     0, 0, 0, 0       // 00:00:00.000
     88   };
     89   scoped_refptr<base::FieldTrial> trial(
     90       base::FieldTrialList::FactoryGetFieldTrial(
     91           "UMA-New-Install-Uniformity-Trial", 100, "Disabled",
     92           2015, 1, 1, base::FieldTrial::ONE_TIME_RANDOMIZED, NULL));
     93   trial->AppendGroup("Control", 50);
     94   trial->AppendGroup("Experiment", 50);
     95   const base::Time start_date = base::Time::FromLocalExploded(kStartDate);
     96   if (install_date < start_date)
     97     trial->Disable();
     98   else
     99     trial->group();
    100 }
    101 
    102 }  // namespace
    103 
    104 void SetupUniformityFieldTrials(const base::Time install_date) {
    105   // The 100 percent field trial in which everyone is a member is a special
    106   // case. It is useful to create as it permits viewing all UMA data in UIs
    107   // and tools that require a field trial.
    108   base::FieldTrial* trial =
    109       base::FieldTrialList::CreateFieldTrial("UMA-Uniformity-Trial-100-Percent",
    110                                              "group_01");
    111   // Call |group()| on the trial to ensure its reported in metrics.
    112   trial->group();
    113 
    114   // One field trial will be created for each entry in this array. The i'th
    115   // field trial will have |trial_sizes[i]| groups in it, including the default
    116   // group. Each group will have a probability of 1/|trial_sizes[i]|.
    117   const int num_trial_groups[] = { 100, 20, 10, 5, 2 };
    118 
    119   // Declare our variation ID bases along side this array so we can loop over it
    120   // and assign the IDs appropriately. So for example, the 1 percent experiments
    121   // should have a size of 100 (100/100 = 1).
    122   const variations::VariationID trial_base_ids[] = {
    123     UNIFORMITY_1_PERCENT_BASE,
    124     UNIFORMITY_5_PERCENT_BASE,
    125     UNIFORMITY_10_PERCENT_BASE,
    126     UNIFORMITY_20_PERCENT_BASE,
    127     UNIFORMITY_50_PERCENT_BASE
    128   };
    129 
    130   const std::string kOneTimeRandomizedTrialName =
    131       "UMA-Uniformity-Trial-%d-Percent";
    132   for (size_t i = 0; i < arraysize(num_trial_groups); ++i) {
    133     SetupSingleUniformityFieldTrial(base::FieldTrial::ONE_TIME_RANDOMIZED,
    134                                     kOneTimeRandomizedTrialName,
    135                                     trial_base_ids[i], num_trial_groups[i]);
    136   }
    137 
    138   // Setup a 5% session-randomized uniformity trial.
    139   const std::string kSessionRandomizedTrialName =
    140       "UMA-Session-Randomized-Uniformity-Trial-%d-Percent";
    141   SetupSingleUniformityFieldTrial(
    142       base::FieldTrial::SESSION_RANDOMIZED, kSessionRandomizedTrialName,
    143       UNIFORMITY_SESSION_RANDOMIZED_5_PERCENT_BASE, 20);
    144 
    145   SetupNewInstallUniformityTrial(install_date);
    146 }
    147 
    148 }  // namespace chrome_variations
    149