concise metrics output (#18)

<img width="525" alt="Screenshot 2023-10-24 at 00 13 41"
src="https://github.com/cap-js/opentelemetry-instrumentation/assets/30337871/9add566d-fd98-4929-8187-c3ea0fba7403">

lib/metrics/CDSConsoleMetricsExporter.js

@@ -3,7 +3,7 @@
 const cds = require('@sap/cds')
 const LOG = cds.log('otel', { label: 'otel:metrics' })
 
-const { ExportResultCode } = require('@opentelemetry/core')
+const { ExportResultCode, hrTimeToTimeStamp } = require('@opentelemetry/core')
 const { ConsoleMetricExporter } = require('@opentelemetry/sdk-metrics')
 
 class CDSConsoleMetricsExporter extends ConsoleMetricExporter {
@@ -18,9 +18,13 @@ class CDSConsoleMetricsExporter extends ConsoleMetricExporter {
 
   static _sendMetrics(metrics, done) {
     for (const scopeMetrics of metrics.scopeMetrics) {
+      const tenant = scopeMetrics.metrics[0].dataPoints[0].attributes['sap.tenancy.tenant_id']
+      const timestamp = hrTimeToTimeStamp(scopeMetrics.metrics[0].dataPoints[0].startTime)
+      let toLog = `db.pool of tenant "${tenant}" at ${timestamp}:`
       for (const metric of scopeMetrics.metrics) {
-        LOG.info(`OTEL Metric ${metric.descriptor.name} | Data Points:`, metric.dataPoints)
+        toLog += `\n       |- ${metric.descriptor.name.replace('db.pool.', '')}: ${metric.dataPoints[0].value}`
       }
+      LOG.info(toLog)
     }
     done({ code: ExportResultCode.SUCCESS })
   }

lib/metrics/db-pool.js

@@ -2,7 +2,7 @@ const cds = require('@sap/cds')
 const LOG = cds.log('otel', { label: 'otel:metrics' })
 
 // REVISIT: instanceof cds.DatabaseService doesn't work with @cap-js databases
-const _kinds = new Set('sqlite', 'hana', 'postgres')
+const _kinds = new Set(['sqlite', 'hana', 'postgres'])
 
 const _initialized = new Set()