Enhance the buffer cache hit ratio calculations for performance metrics

CHANGELOG.next.asciidoc

@@ -326,6 +326,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 - Add SSL support for aerospike module {pull}38126[38126]
 - Add last_terminated_timestamp metric in kubernetes module {pull}39200[39200] {issue}3802[3802]
 - Add pod.status.ready_time and pod.status.reason metrics in kubernetes module {pull}39316[39316]
+- Add "Buffer cache hit ratio base" to calculate "Buffer cache hit ratio" for performance metrics {pull}40022[40022]
 
 
 *Metricbeat*

x-pack/metricbeat/module/mssql/performance/performance.go

@@ -65,6 +65,9 @@ func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
 func (m *MetricSet) Fetch(reporter mb.ReporterV2) {
 	var err error
 	var rows *sql.Rows
+	var buffer_cache_hit_ratio, buffer_cache_hit_ratio_base int64
+	bufferCacheHitRatio := "Buffer cache hit ratio"
+	bufferCacheHitRatioBase := "Buffer cache hit ratio base"
 	rows, err = m.db.Query(`SELECT object_name,
        counter_name,
        instance_name,
@@ -80,6 +83,7 @@ WHERE  counter_name = 'SQL Compilations/sec'
              AND instance_name = '_Total' )
         OR ( counter_name IN ( 'Page life expectancy', 
                   'Buffer cache hit ratio', 
+	          'Buffer cache hit ratio base',
                   'Target pages', 'Database pages', 
                   'Checkpoint pages/sec' )
              AND object_name LIKE '%:Buffer Manager%' )
@@ -112,13 +116,20 @@ WHERE  counter_name = 'SQL Compilations/sec'
 		row.instanceName = strings.TrimSpace(row.instanceName)
 		row.objectName = strings.TrimSpace(row.objectName)
 
-		if row.counterName == "Buffer cache hit ratio" {
-			mapStr[row.counterName] = fmt.Sprintf("%v", float64(*row.counterValue)/100)
-		} else {
+		switch row.counterName {
+		case bufferCacheHitRatio:
+			buffer_cache_hit_ratio = *row.counterValue
+		case bufferCacheHitRatioBase:
+			buffer_cache_hit_ratio_base = *row.counterValue
+		default:
 			mapStr[row.counterName] = fmt.Sprintf("%v", *row.counterValue)
 		}
 	}
 
+	if buffer_cache_hit_ratio_base != 0 {
+		mapStr[bufferCacheHitRatio] = fmt.Sprintf("%f", float64(buffer_cache_hit_ratio)/float64(buffer_cache_hit_ratio_base))
+	}
+
 	res, err := schema.Apply(mapStr)
 	if err != nil {
 		m.log.Error(fmt.Errorf("error applying schema %w", err))