[batchprocessor] fix broken processor_batch_metadata_cardinality metric (open-telemetry#10232)

Fixes open-telemetry#10231

Signed-off-by: Alex Boten <[email protected]>

Author: codeboten

.chloggen/codeboten_fix-batchprocessor-bug.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: batchprocessor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fixing processor_batch_metadata_cardinality which was broken in v0.101.0
+
+# One or more tracking issues or pull requests related to the change
+issues: [10231]
+
+# (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:
+
+# 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: []

processor/batchprocessor/metrics.go

@@ -70,8 +70,8 @@ func (bpt *batchProcessorTelemetry) createOtelMetrics(set component.TelemetrySet
 	errors = multierr.Append(errors, err)
 
 	bpt.batchMetadataCardinality, err = meter.Int64ObservableUpDownCounter(
-		processorhelper.BuildCustomMetricName(typeStr, ""),
-		metric.WithDescription(""),
+		processorhelper.BuildCustomMetricName(typeStr, "metadata_cardinality"),
+		metric.WithDescription("Number of distinct metadata value combinations being processed"),
 		metric.WithUnit("1"),
 		metric.WithInt64Callback(func(_ context.Context, obs metric.Int64Observer) error {
 			obs.Observe(int64(currentMetadataCardinality()))