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Examples of custom metric usages

• Some useful metrics may not be provided yet and user registers own.
• Metrics for load balancing.
• Various metrics of business processes or related to user application.
• Security-related metrics.

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• Custom Metrics are based on the New Metric System.
• Custom metric name always begins with the prefix "custom.".

• GridMetricManager handles custom metrics.

• Allow registration of simple metrics like LongMetric, DoubleMetric, ObjectMetric which is can be exported by the existing metric exporters (like JMX )exporter.
• Custom metrics management requires might require a permission.
• We should document examples of effecient metrics implementations like LongAdder.

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package org.apache.ignite;
public interface IgniteMetrics {
     

/

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*

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*

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<T extends Metric> T metric(T metric);
/**
 * Custom metric manager. Allows to add own metrics in registers with names starting with "custom.".
 */
public interface IgniteMetrics {
    /**
     * Registers metric in register 'custom.' + {@code registryName}. Adds new register if absent.
     *
     * @return New {@code metric} or previous metric if it already exists with the same name.
     */
    <T extends Metric> T metric(String registryName, String metricName, T metric);

    /** Removes metric from register 'custom.' + {@code registryName}. */
    void removeMetric(String registryName, String metricName);

    /** @return Metric registry named '"custom." + {@code registryName}'. */
    ReadOnlyMetricRegistry registry(String registryName);

    /** @return Removes registry named '"custom." + {@code registryName}'. */
    ReadOnlyMetricRegistry removeRegistry(String registryName);


    // Simple type metrics.

    /**
     * Registers a {@link LongMetric} in register 'custom.' + {@code registryName}. Adds registry if absent.
     *
     * @return New or previously registered long value setter.
     */
    LongConsumer longMetric(String registryName, String metricName, @Nullable String description);

    /**
     * Registers a {@link DoubleMetric} in register 'custom.' + {@code registryName}. Adds registry if absent.
     *
     * @return New or previously registered double value setter.
     */
    DoubleConsumer doubleMetric(String registryName, String metricName, @Nullable String description);

    /**
     * Registers a {@link BooleanMetric} in register 'custom.' + {@code registryName}. Adds registry if absent.
     *
     * @return New or previously registered boolean value setter.
     */
    Consumer<Boolean> booleanMetric(String registryName, String metricName, @Nullable String description);

    /**
     * Registers a {@link ObjectMetric} in register 'custom.' + {@code registryName}. Adds registry if absent.
     *
     * @return New or previously registered object setter.
     */
    <T> Consumer<T> objectMetric(String registryName, String metricName, Class<T> valueType, @Nullable String description);


    // Might be useful the gauges:

    /**
     * Registers a {@link LongMetric} metric in register 'custom.' + {@code registryName} with long value supplier {@code valueSupplier}. 
     * Adds registry if absent.
     *
     * @return {@code True} if metric was added. {@code False} if another meric already exists under the same name.  
     */
    boolean longMetric(String registryName, String metricName, LongSupplier valueSupplier, @Nullable String description);

    /**
     * Registers a {@link DoubleMetric} metric in register 'custom.' + {@code registryName} with double value supplier {@code valueSupplier}. 
     * Adds registry if absent.
     *
     * @return {@code True} if metric was added. {@code False} if another meric already exists under the same name.  
     */
    boolean doubleMetric(String registryName, String metricName, DoubleSupplier valueSupplier, @Nullable String description);

    /**
     * Registers a {@link BooleanMetric} metric in register 'custom.' + {@code registryName} with boolean value supplier {@code valueSupplier}. 
     * Adds registry if absent.
     *
     * @return {@code True} if metric was added. {@code False} if another meric already exists under the same name.  
     */
    boolean booleanMetric(String registryName, String metricName, BooleanSupplier valueSupplier, @Nullable String description);

    /**
     * Registers a {@link ObjectMetric} metric in register 'custom.' + {@code registryName} with object value supplier {@code valueSupplier}. 
     * Adds registry if absent.
     *
     * @return {@code True} if metric was added. {@code False} if another meric already exists under the same name.  
     */
    <T> boolean objectMetric(String registryName, String metricName, Class<T> valueType, Supplier<T> valueSupplier, @Nullable String description);
}

Risks and Assumptions

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• Custom metrics can affect the performance.
• We do not provide varuous useful metric implementatons.
• Custom metrics aren't stored and require re-registration after node restart. At least at the first phase.

Phases

In future, we could expose 

1. Implementation of the described API.
2. Extending the API with metrics like Histogram, HitRate. Allowing to configure metrics.
3. Storing registered custom metrics with their configurations.

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