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SOLR-14683: move "Missing Metrics" section down to config section; add short blurb to intro text
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Cassandra Targett
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@ -26,51 +26,16 @@ Internally this feature uses the http://metrics.dropwizard.io[Dropwizard Metrics
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* *timers* - measure the number and duration of events. They provide a count and histogram of timings.
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* *gauges* - offer instantaneous reading of a current value, e.g., current queue depth, current number of active connections, free heap size.
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Some of these meters may be missing or empty for any number of valid reasons.
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In these cases, missing values of any type will be returned as `null` by default so empty values won't impact averages or histograms.
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This is configurable for several types of missing values; see the <<The <metrics> <missingValues> Element>> section below.
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Each group of related metrics with unique names is managed in a *metric registry*. Solr maintains several such registries, each corresponding to a high-level group such as: `jvm`, `jetty`, `node`, and `core` (see <<Metric Registries>> below).
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For each group (and/or for each registry) there can be several *reporters*, which are components responsible for communication of metrics from selected registries to external systems. Currently implemented reporters support emitting metrics via JMX, Ganglia, Graphite and SLF4J.
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There is also a dedicated `/admin/metrics` handler that can be queried to report all or a subset of the current metrics from multiple registries.
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=== Missing metrics
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Long-lived metrics values are still reported when the underlying value is unavailable (eg. "INDEX.sizeInBytes" when
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IndexReader is closed). Short-lived transient metrics (such as cache entries) that are properties of complex gauges
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(internally represented as `MetricsMap`) are simply skipped when not available, and neither their names nor values
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appear in registries (or in /admin/metrics reports).
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When a missing value is encountered by default it's reported as null value, regardless of the metrics type.
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This can be configured in the `solr.xml:/solr/metrics/missingValues` element, which recognizes the following child elements
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(for string elements a JSON payload is supported):
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`nullNumber`::
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value to use when a missing (null) numeric metrics value is encountered.
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`notANumber`::
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value to use when an invalid numeric value is encountered.
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`nullString`::
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value to use when a missing (null) string metrics is encountered.
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`nullObject`::
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value to use when a missing (null) complex object is encountered.
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Example configuration that returns null for missing numbers, -1 for
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invalid numeric values, empty string for missing strings, and a Map for missing
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complex objects:
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[source,xml]
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----
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<metrics>
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<missingValues>
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<null name="nullNumber"/>
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<int name="notANumber">-1</int>
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<str name="nullString"></str>
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<str name="nullObject">{"value":"missing"}</str>
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</missingValues>
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</metrics>
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----
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== Metric Registries
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Solr includes multiple metric registries, which group related metrics.
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@ -202,6 +167,45 @@ As an example of a section of `solr.xml` that defines some of these custom param
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</metrics>
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----
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=== The <metrics> <missingValues> Element
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Long-lived metrics values are still reported when the underlying value is unavailable (e.g., "INDEX.sizeInBytes" when
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IndexReader is closed). Short-lived transient metrics (such as cache entries) that are properties of complex gauges
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(internally represented as `MetricsMap`) are simply skipped when not available, and neither their names nor values
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appear in registries (or in `/admin/metrics` reports).
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When a missing value is encountered by default it's reported as null value, regardless of the metrics type.
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This can be configured in the `solr.xml:/solr/metrics/missingValues` element, which recognizes the following child elements
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(for string elements a JSON payload is supported):
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`nullNumber`::
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The value to use when a missing (null) numeric metrics value is encountered.
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`notANumber`::
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The value to use when an invalid numeric value is encountered.
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`nullString`::
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The value to use when a missing (null) string metrics is encountered.
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`nullObject`::
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The value to use when a missing (null) complex object is encountered.
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Example configuration that returns null for missing numbers, -1 for
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invalid numeric values, empty string for missing strings, and a Map for missing
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complex objects:
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[source,xml]
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----
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<metrics>
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<missingValues>
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<null name="nullNumber"/>
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<int name="notANumber">-1</int>
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<str name="nullString"></str>
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<str name="nullObject">{"value":"missing"}</str>
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</missingValues>
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</metrics>
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----
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== Reporters
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Reporter configurations are specified in `solr.xml` file in `<metrics><reporter>` sections, for example:
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