This describes how to write client code to collect UKM data. Before you add new metrics, you should file a proposal. See go/ukm for more information.
Any events and metrics you collect need to be documented in //tools/metrics/ukm/ukm.xml
owner: the email of someone who can answer questions about how this metric is recorded, what it means, and how it should be used. Can include multiple people.summary of the event about which you are recording details, including a description of when the event will be recorded.summary of the data and what it means.enum type if the metric is enumerated. The enum uses the //tools/metrics/histograms/enums.xml file for definitions. Note this is the same file for UMA histogram definitions so these can ideally be reused.unit should be included.singular="true".<event name="Goat.Teleported"> <owner>teleporter@chromium.org</owner> <summary> Recorded when a page teleports a goat. </summary> <metric name="Duration" unit="ms"> <summary> How long it took to teleport. </summary> </metric> <metric name="GoatType" enum="GoatType"> <summary> The type of goat that was teleported. </summary> </metric> </event>
Control of which metrics are included in the History table is done via the same tools/metrics/ukm/ukm.xml file in the Chromium codebase. To have a metric aggregated, <aggregation> and <history> tags need to be added.
<event name="Goat.Teleported"> <metric name="Duration"> ... <aggregation> <history> <index fields="profile.country"/> <statistics> <quantiles type="std-percentiles"/> </statistics> </history> </aggregation> ... </metric> </event>
Supported statistic types are:
<quantiles type="std-percentiles"/>: Calculates the “standard percentiles” for the values which are 1, 5, 10, 25, 50, 75, 90, 95, and 99%ile.<enumeration/>: Calculates the proportions of all values individually. The proportions indicate the relative frequency of each bucket and are calculated independently for each metric over each aggregation. (Details below.)There can also be one or more index tags which define additional aggregation keys. These are a comma-separated list of keys that is appended to the standard set. These additional keys are optional but, if present, are always present together. In other words, “fields=profile.county,profile.form_factor” will cause all the standard aggregations plus each with both country and form_factor but not with all the standard aggregations (see above) plus only one of them. If individual and combined versions are desired, use multiple index tags.
Currently supported additional index fields are:
profile.countryprofile.form_factorprofile.system_ramWARNING: This feature is still under development and isn't ready for use.
Proportions are calculated against the number of “page loads” (meaning per “source” which is usually but not always the same as a browser page load) that emitted one or more values for the enumeration. The proportions will sum to 1.0 for an enumeration that emits only one result per page-load if it emits anything at all. An enumeration emitted more than once per source will result in proportions that total greater than 1.0 but are still relative to the total number of loads. If an individual value is emitted more than once per source, that value's proportion will be greater than 1.0.
For example, Security.SiteEngagement emits one value (either 4 or 2) per source:
A proportion calculated over all sources would sum to 1.0:
In contrast, VirtualKeyboard.Open:TextInputType emits multiple values per source, and can emit the same value multiple times per source. The sum of the proportions for VirtualKeyboard.Open:TextInputType will be greater that 1.0, and some proportions will be greater than 1.0. In the following example, TextInputType is emitted multiple times per source, and TextInputType=4 is emitted more than once per source:
A proportion calculated over all sources would be:
The denominator for each is 3 because there were 3 sources reporting the metric. The numerator for each enum value is the count of how many times the value was emitted.
In order to record UKM events, your code needs a UkmRecorder object, defined by //services/metrics/public/cpp/ukm_recorder.h
There are two main ways of getting a UkmRecorder instance.
Use ukm::UkmRecorder::Get(). This currently only works from the Browser process.
Use a service connector and get a UkmRecorder.
std::unique_ptr<ukm::UkmRecorder> ukm_recorder = ukm::UkmRecorder::Create(context()->connector()); ukm::builders::MyEvent(source_id) .SetMyMetric(metric_value) .Record(ukm_recorder.get());
UKM identifies navigations by their source ID and you'll need to associate an ID with your event in order to tie it to a main frame URL. Preferably, get an existing ID for the navigation from another object.
The main method for doing this is by getting a navigation ID:
ukm::SourceId source_id = GetSourceIdForWebContentsDocument(web_contents); ukm::SourceId source_id = ukm::ConvertToSourceId( navigation_handle->GetNavigationId(), ukm::SourceIdType::NAVIGATION_ID);
Some events however occur in the background, and a navigation ID does not exist. In that case, you can use the ukm::UkmBackgroundRecorderService to check whether the event can be recorded. This is achieved by using the History Service to determine whether the event's origin is still present in the user profile.
// Add the service as a dependency in your service's constructor. DependsOn(ukm::UkmBackgroundRecorderFactory::GetInstance()); // Get an instance of the UKM service using a Profile. auto* ukm_background_service = ukm::UkmBackgroundRecorderFactory::GetForProfile(profile); // Check if recording a background event for |origin| is allowed. ukm_background_service->GetBackgroundSourceIdIfAllowed(origin, base::BindOnce(&DidGetBackgroundSourceId)); // A callback will run with an optional source ID. void DidGetBackgroundSourceId(base::Optional<ukm::SourceId> source_id) { if (!source_id) return; // Can't record as it wasn't found in the history. // Use the newly generated source ID. ukm::builders::MyEvent(*source_id) .SetMyMetric(metric_value) .Record(ukm_recorder.get()); }
For the remaining cases you may need to temporarily create your own IDs and associate the URL with them. However we currently prefer that this method is not used, and if you need to setup the URL yourself, please email us first at ukm-team@google.com. Example:
ukm::SourceId source_id = ukm::UkmRecorder::GetNewSourceID(); ukm_recorder->UpdateSourceURL(source_id, main_frame_url);
You will also need to add your class as a friend of UkmRecorder in order to use this private API.
Helper objects for recording your event are generated from the descriptions in ukm.xml. You can use them like so:
#include "services/metrics/public/cpp/ukm_builders.h" void OnGoatTeleported() { ... ukm::builders::Goat_Teleported(source_id) .SetDuration(duration.InMilliseconds()) .SetType(goat_type) .Record(ukm_recorder); }
If the event name in the XML contains a period (.), it is replaced with an underscore (_) in the method name.
Build Chromium and run it with ‘--force-enable-metrics-reporting --metrics-upload-interval=N’. You may want some small N if you are interested in seeing behavior when UKM reports are emitted. Trigger your event locally and check chrome://ukm to make sure the data was recorded correctly.
You can pass your code a TestUkmRecorder (see //components/ukm/test_ukm_recorder.h) and then use the methods it provides to test that your data records correctly.