[receiver/elasticsearch] Add active index merge count metric (#34388)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
This adds a metric for the currently active index merges to help monitor
the status of an Elasticsearch cluster.

**Link to tracking Issue:** <Issue number if applicable>
Resolves
#34387

**Testing:** <Describe what testing was performed and which tests were
added.>
Updated existing tests to account for enabled metric.

.chloggen/es_add_metric.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: elasticsearchreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add metric for active index merges
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [34387]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

receiver/elasticsearchreceiver/documentation.md

@@ -852,6 +852,20 @@ The number of documents for an index.
 | state | The state of the document. | Str: ``active``, ``deleted`` |
 | aggregation | Type of shard aggregation for index statistics | Str: ``primary_shards``, ``total`` |
 
+### elasticsearch.index.operations.merge.current
+
+The number of currently active segment merges
+
+| Unit | Metric Type | Value Type |
+| ---- | ----------- | ---------- |
+| {merges} | Gauge | Int |
+
+#### Attributes
+
+| Name | Description | Values |
+| ---- | ----------- | ------ |
+| aggregation | Type of shard aggregation for index statistics | Str: ``primary_shards``, ``total`` |
+
 ### elasticsearch.index.operations.merge.docs_count
 
 The total number of documents in merge operations for an index.

receiver/elasticsearchreceiver/internal/metadata/testdata/config.yaml

@@ -41,6 +41,8 @@ all_set:
       enabled: true
     elasticsearch.index.operations.completed:
       enabled: true
+    elasticsearch.index.operations.merge.current:
+      enabled: true
     elasticsearch.index.operations.merge.docs_count:
       enabled: true
     elasticsearch.index.operations.merge.size:
@@ -234,6 +236,8 @@ none_set:
       enabled: false
     elasticsearch.index.operations.completed:
       enabled: false
+    elasticsearch.index.operations.merge.current:
+      enabled: false
     elasticsearch.index.operations.merge.docs_count:
       enabled: false
     elasticsearch.index.operations.merge.size:

receiver/elasticsearchreceiver/internal/model/nodestats.go

@@ -215,6 +215,7 @@ type BasicIndexOperation struct {
 
 type MergeOperations struct {
 	BasicIndexOperation
+	Current          int64 `json:"current"`
 	TotalSizeInBytes int64 `json:"total_size_in_bytes"`
 	TotalDocs        int64 `json:"total_docs"`
 }

receiver/elasticsearchreceiver/metadata.yaml

@@ -890,6 +890,13 @@ metrics:
       value_type: int
     attributes: [index_aggregation_type]
     enabled: false
+  elasticsearch.index.operations.merge.current:
+    description: The number of currently active segment merges
+    unit: "{merges}"
+    gauge:
+      value_type: int
+    attributes: [ index_aggregation_type ]
+    enabled: false
   elasticsearch.index.segments.count:
     description: Number of segments of an index.
     unit: "{segments}"

receiver/elasticsearchreceiver/scraper.go

@@ -562,6 +562,10 @@ func (r *elasticsearchScraper) scrapeOneIndexMetrics(now pcommon.Timestamp, name
 		now, stats.Total.MergeOperations.TotalDocs, metadata.AttributeIndexAggregationTypeTotal,
 	)
 
+	r.mb.RecordElasticsearchIndexOperationsMergeCurrentDataPoint(
+		now, stats.Total.MergeOperations.Current, metadata.AttributeIndexAggregationTypeTotal,
+	)
+
 	r.mb.RecordElasticsearchIndexShardsSizeDataPoint(
 		now, stats.Total.StoreInfo.SizeInBy, metadata.AttributeIndexAggregationTypeTotal,
 	)

receiver/elasticsearchreceiver/scraper_test.go

@@ -43,6 +43,7 @@ func TestScraper(t *testing.T) {
 
 	config.Metrics.ElasticsearchIndexOperationsMergeSize.Enabled = true
 	config.Metrics.ElasticsearchIndexOperationsMergeDocsCount.Enabled = true
+	config.Metrics.ElasticsearchIndexOperationsMergeCurrent.Enabled = true
 	config.Metrics.ElasticsearchIndexSegmentsCount.Enabled = true
 	config.Metrics.ElasticsearchIndexSegmentsSize.Enabled = true
 	config.Metrics.ElasticsearchIndexSegmentsMemory.Enabled = true
@@ -100,6 +101,7 @@ func TestScraperNoIOStats(t *testing.T) {
 
 	config.Metrics.ElasticsearchIndexOperationsMergeSize.Enabled = true
 	config.Metrics.ElasticsearchIndexOperationsMergeDocsCount.Enabled = true
+	config.Metrics.ElasticsearchIndexOperationsMergeCurrent.Enabled = true
 	config.Metrics.ElasticsearchIndexSegmentsCount.Enabled = true
 	config.Metrics.ElasticsearchIndexSegmentsSize.Enabled = true
 	config.Metrics.ElasticsearchIndexSegmentsMemory.Enabled = true

receiver/elasticsearchreceiver/testdata/expected_metrics/full_linux.yaml

@@ -505,6 +505,18 @@ resourceMetrics:
                   timeUnixNano: "2000000"
               isMonotonic: true
             unit: '{operations}'
+          - description: The number of currently active segment merges
+            gauge:
+              dataPoints:
+                - asInt: "0"
+                  attributes:
+                    - key: aggregation
+                      value:
+                        stringValue: total
+                  startTimeUnixNano: "1000000"
+                  timeUnixNano: "2000000"
+            name: elasticsearch.index.operations.merge.current
+            unit: '{merges}'
           - description: The total number of documents in merge operations for an index.
             name: elasticsearch.index.operations.merge.docs_count
             sum:
@@ -1285,6 +1297,18 @@ resourceMetrics:
                   timeUnixNano: "2000000"
               isMonotonic: true
             unit: '{operations}'
+          - description: The number of currently active segment merges
+            gauge:
+              dataPoints:
+                - asInt: "0"
+                  attributes:
+                    - key: aggregation
+                      value:
+                        stringValue: total
+                  startTimeUnixNano: "1000000"
+                  timeUnixNano: "2000000"
+            name: elasticsearch.index.operations.merge.current
+            unit: '{merges}'
           - description: The total number of documents in merge operations for an index.
             name: elasticsearch.index.operations.merge.docs_count
             sum:
@@ -2298,17 +2322,17 @@ resourceMetrics:
               aggregationTemporality: 2
               dataPoints:
                 - asInt: "15746158592"
-                  startTimeUnixNano: "2000000"
-                  timeUnixNano: "1000000"
+                  startTimeUnixNano: "1000000"
+                  timeUnixNano: "2000000"
             unit: By
           - description: The amount of disk space across all file stores for this node.
             name: elasticsearch.node.fs.disk.total
             sum:
               aggregationTemporality: 2
               dataPoints:
                 - asInt: "67371577344"
-                  startTimeUnixNano: "2000000"
-                  timeUnixNano: "1000000"
+                  startTimeUnixNano: "1000000"
+                  timeUnixNano: "2000000"
             unit: By
           - description: The number of HTTP connections to the node.
             name: elasticsearch.node.http.connections