:jbake-type: page
:jbake-status: published

= Apache Tamaya - Extension: Usage Tracking

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[[UsageTracker]]
== Tamaya Usage Tracking (Extension Module)

Tamaya _UsageTracker_ is an extension module. Refer to the link:../extensions.html[extensions documentation] for further details.


=== What functionality this module provides ?

Tamaya _UsageTracker_ allows to record and count the configuration access and consumer locations in your local
VM.


=== Compatibility

The module is based on Java 8.


=== Installation

To use Tamaya _usagetracker_ you only must add the corresponding dependency to your module:

[source, xml, subs=attributes+]
-----------------------------------------------
<dependency>
  <groupId>org.apache.tamaya.ext</groupId>
  <artifactId>tamaya-usagetracker</artifactId>
  <version>{tamaya_version}</version>
</dependency>
-----------------------------------------------


=== Tracking Configuration Access

The model module also allows tracking which code accesses configuration properties or configuration parameters.
It checks the stacktrace to evaluate the calling code location, hereby any unwanted packages can be implicitly
ommitted from the stacktrace. Also the maximal length of the stacktrace retained can be constraint in length.
The usages are recorded as +Usage+ instances. Hereby for each parameter accessed a corresponding +Usage+
instance is created. It can be accessed by calling +Usage ConfigUsageStats.getUsage(String key)+. Usage
statistics for calling +Configuration.getProperties()+ can be obtained calling +Usage getUsageAllProps();+.

Usage tracking is disabled by default. It can be enabled by calling +ConfigUsageStats.enableUsageTracking(true);+.
+ConfigUsageStats.isUsageTrackingEnabled()+ returns the current tracking status.

The +Usage+ class itself provides access to further fainer grained usage data (+AccessDetail+) containing:

* the access point (+fqn.ClassName#method(line: xxx)+).
* the number of accesses
* the first an last access
* the values read
* the access stacktrace (filtered by ignored packages).

[source,java]
-----------------------------------------------------------
public final class Usage {
    [...]
    public String getKey();
    public void clearMetrics();
    public int getReferenceCount();
    public int getUsageCount();
    public Collection<AccessDetail> getAccessDetails(Class type);
    public Collection<AccessDetail> getAccessDetails(Package pack);
    public Collection<AccessDetail> getAccessDetails(String lookupExpression);
    public Collection<AccessDetail> getAccessDetails();
    public void trackUsage(String value);
    public void trackUsage(String value, int maxTraceLength);


    public static final class AccessDetail {
        [...]
        public void clearStats();
        public long trackAccess(String value);
        public long getAccessCount();
        public String getAccessPoint();
        public long getFirstAccessTS();
        public long getLastAccessTS();
        public String[] getStackTrace();
        public Map<Long, String> getTrackedValues();
    }

}
-----------------------------------------------------------

With +ConfigUsageStats.clearUsageStats()+ the collected statistics can be reset at any time. Summarizing the main
singleton for configuration statistics is defined as follows:

[source,java]
-----------------------------------------------------------
public final class ConfigUsage{
    public static ConfigUsage getInstance();
    public static ConfigUsage getInstance(ClassLoader classLoader);

    public Set<String> getIgnoredUsagePackages();
    public void addIgnoredUsagePackages(String... packageName);
    public void enableUsageTracking(boolean enabled);
    public Usage getUsage(String key);
    public Collection<Usage> getUsages();
    public void clearUsageStats();
    public Usage getUsageAllProperties();
    public boolean isUsageTrackingEnabled();
    public String getUsageInfo();
}
-----------------------------------------------------------


==== Customizing the Stacktrace for Usage Reporting

The stacktrace tracked by the system can be customized in several ways:

* +ConfigUsageStats.addIgnoredPackageNames(String...)+ allows to add additional ignored package names.
* With +Usage.setMaxTraceLength(int)+ the maximal size of the stacktraces logged can be set. Setting a
  negative value will disable stacktrace logging completelely.


=== Accessing Usage Statistics

Bascially usage statistics are available in two forms:

* The +Usage/AccessDetail+ object tree can be accessed programmatically from the +ConfigUsageStats+
  singleton.
* With +ConfigUsageStats.getUsageInfo()+ also a textual representation of the usage statistics
  can be obtained, as illustrated below (a snipped from the current test output):

[source,listing]
-----------------------------------------------------------
Apache Tamaya Configuration Usage Metrics
=========================================
DATE: Sat Apr 30 21:51:09 CEST 2016

220    <<all>>:
  - 220   <unknown/filtered/internal>                       , first=Sat Apr 30 21:51:09 CEST 2016, last=Sat Apr 30 21:51:09 CEST 2016
3      java.version:
  - 2     test.model.TestConfigAccessor#readProperty(line:43), first=Sat Apr 30 21:51:09 CEST 2016, last=Sat Apr 30 21:51:09 CEST 2016
  - 1     <unknown/filtered/internal>                       , first=Sat Apr 30 21:51:09 CEST 2016, last=Sat Apr 30 21:51:09 CEST 2016

-----------------------------------------------------------


=== Auto-Documentation of Classes with Configuration Injection

A special feature of this module is that it observes +ConfigEvent+ published through Tamaya'as event channel
(+tamaya-events+ module). If no metaconfiguration model is found the model manager by default automatically creates
models for all injected instances on the fly. In the case of CDI integration this happens typically during deployment
time, since CDI initializes during deployment time. Other runtime platforms, such as OSGi, may have rather different
behaviour. Nevertheless this means that after your system has been started you should have access to a complete
set of +ConfigModel+ instances that automatically document all the classes in your system that consume configuration
(through injection).


== UsageTracker Module SPI

=== The ConfigUsageStatsSpi

The methods for managing and tracking of configuration changes are similarly delegated to an
implementation of the +org.apache.tamaya.model.spi.ConfigUsageStatsSpi+ SPI.
By implementing this SPI and registerting it with the +ServiceContext+ the usage tracking
logic can be adapted or replaced.