metricbeat/module/mongodb/replstatus: Update getOpTimestamp in `rep…

…lstatus` to fix sort and temp files generation issue (#37688)

* Update getOpTimestamp implementation

CHANGELOG.next.asciidoc

@@ -194,6 +194,7 @@ Setting environmental variable ELASTIC_NETINFO:false in Elastic Agent pod will d
 - Add a `/inputs/` route to the HTTP monitoring endpoint that exposes metrics for each metricset instance. {pull}36971[36971]
 - Add linux IO metrics to system/process {pull}37213[37213]
 - Add new memory/cgroup metrics to Kibana module {pull}37232[37232]
+- Update `getOpTimestamp` in `replstatus` to fix sort and temp files generation issue in mongodb. {pull}37688[37688]
 
 *Osquerybeat*
 

metricbeat/module/mongodb/replstatus/info.go

@@ -21,11 +21,10 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"time"
 
 	"go.mongodb.org/mongo-driver/bson"
-	"go.mongodb.org/mongo-driver/bson/primitive"
 	"go.mongodb.org/mongo-driver/mongo"
-	"go.mongodb.org/mongo-driver/mongo/options"
 )
 
 type oplogInfo struct {
@@ -71,14 +70,9 @@ func getReplicationInfo(client *mongo.Client) (*oplogInfo, error) {
 	}
 
 	// get first and last items in the oplog
-	firstTs, err := getOpTimestamp(collection, "$natural")
+	firstTs, lastTs, err := getOpTimestamp(collection)
 	if err != nil {
-		return nil, fmt.Errorf("could not get first operation timestamp in op log: %w", err)
-	}
-
-	lastTs, err := getOpTimestamp(collection, "-$natural")
-	if err != nil {
-		return nil, fmt.Errorf("could not get last operation timestamp in op log: %w", err)
+		return nil, fmt.Errorf("could not get operation timestamp in op log: %w", err)
 	}
 
 	diff := lastTs - firstTs
@@ -92,28 +86,35 @@ func getReplicationInfo(client *mongo.Client) (*oplogInfo, error) {
 	}, nil
 }
 
-func getOpTimestamp(collection *mongo.Collection, sort string) (uint32, error) {
-	opt := options.Find().SetSort(bson.D{{Key: sort, Value: 1}})
-	cursor, err := collection.Find(context.Background(), bson.D{}, opt)
-	if err != nil {
-		return 0, fmt.Errorf("could not get cursor on collection '%s': %w", collection.Name(), err)
+func getOpTimestamp(collection *mongo.Collection) (uint32, uint32, error) {
+
+	// Find both first and last timestamps using $min and $max
+	pipeline := bson.A{
+		bson.M{"$group": bson.M{"_id": 1, "minTS": bson.M{"$min": "$ts"}, "maxTS": bson.M{"$max": "$ts"}}},
 	}
 
-	if !cursor.Next(context.Background()) {
-		return 0, errors.New("objects not found in local.oplog.rs")
+	cursor, err := collection.Aggregate(context.Background(), pipeline)
+	if err != nil {
+		return 0, 0, fmt.Errorf("could not get operation timestamps in op log: %w", err)
 	}
+	defer cursor.Close(context.Background())
 
-	var opTime map[string]interface{}
-	if err = cursor.Decode(&opTime); err != nil {
-		return 0, fmt.Errorf("error decoding response: %w", err)
+	var result struct {
+		MinTS time.Time `bson:"minTS"`
+		MaxTS time.Time `bson:"maxTS"`
 	}
 
-	ts, ok := opTime["ts"].(primitive.Timestamp)
-	if !ok {
-		return 0, errors.New("an expected timestamp was not found")
+	if !cursor.Next(context.Background()) {
+		return 0, 0, errors.New("no documents found in op log")
 	}
+	if err := cursor.Decode(&result); err != nil {
+		return 0, 0, fmt.Errorf("error decoding response for timestamps: %w", err)
+	}
+
+	minTS := uint32(result.MinTS.Unix())
+	maxTS := uint32(result.MaxTS.Unix())
 
-	return ts.T, nil
+	return minTS, maxTS, nil
 }
 
 func contains(s []string, x string) bool {