Improve GetUsedNodes function

internal/repository/job.go

@@ -66,6 +66,7 @@ import (
 	"fmt"
 	"maps"
 	"math"
+	"sort"
 	"strconv"
 	"sync"
 	"time"
@@ -76,7 +77,6 @@ import (
 	"github.com/ClusterCockpit/cc-lib/v2/schema"
 	sq "github.com/Masterminds/squirrel"
 	"github.com/jmoiron/sqlx"
-	"github.com/xtgo/set"
 )
 
 var (
@@ -774,7 +774,16 @@ func (r *JobRepository) UpdateFootprint(
 	return stmt.Set("footprint", string(rawFootprint)), nil
 }
 
-func (r *JobRepository) GetUsedNodes(ts uint64) map[string][]string {
+// GetUsedNodes returns a map of cluster names to sorted lists of unique hostnames
+// that are currently in use by jobs that started before the given timestamp and
+// are still in running state.
+//
+// The timestamp parameter (ts) is compared against job.start_time to find
+// relevant jobs. Returns an error if the database query fails or row iteration
+// encounters errors. Individual row parsing errors are logged but don't fail
+// the entire operation.
+func (r *JobRepository) GetUsedNodes(ts uint64) (map[string][]string, error) {
+	// Note: Query expects index on (job_state, start_time) for optimal performance
 	q := sq.Select("job.cluster", "job.resources").From("job").
 		Where("job.start_time < ?", ts).
 		Where(sq.Eq{"job.job_state": "running"})
@@ -782,8 +791,7 @@ func (r *JobRepository) GetUsedNodes(ts uint64) map[string][]string {
 	rows, err := q.RunWith(r.stmtCache).Query()
 	if err != nil {
 		queryString, queryVars, _ := q.ToSql()
-		cclog.Errorf("Error while running query '%s' %v: %v", queryString, queryVars, err)
+		return nil, fmt.Errorf("query failed [%s] %v: %w", queryString, queryVars, err)
-		return nil
 	}
 	defer rows.Close()
 
@@ -794,16 +802,25 @@ func (r *JobRepository) GetUsedNodes(ts uint64) map[string][]string {
 		cluster      string
 		rawResources []byte
 		resources    []*schema.Resource
+		skippedRows  int
 	)
 
 	for rows.Next() {
 		if err := rows.Scan(&cluster, &rawResources); err != nil {
 			cclog.Warnf("Error scanning job row in GetUsedNodes: %v", err)
+			skippedRows++
 			continue
 		}
 
+		resources = resources[:0] // Clear slice, keep capacity
 		if err := json.Unmarshal(rawResources, &resources); err != nil {
 			cclog.Warnf("Error unmarshaling resources for cluster %s: %v", cluster, err)
+			skippedRows++
+			continue
+		}
+
+		if len(resources) == 0 {
+			cclog.Debugf("Job in cluster %s has no resources", cluster)
 			continue
 		}
 
@@ -817,19 +834,23 @@ func (r *JobRepository) GetUsedNodes(ts uint64) map[string][]string {
 	}
 
 	if err := rows.Err(); err != nil {
-		cclog.Errorf("Error iterating rows in GetUsedNodes: %v", err)
+		return nil, fmt.Errorf("error iterating rows: %w", err)
 	}
 
-	nodeList := make(map[string][]string)
+	if skippedRows > 0 {
+		cclog.Warnf("GetUsedNodes: Skipped %d rows due to parsing errors", skippedRows)
+	}
+
+	// Convert sets to sorted slices
+	nodeList := make(map[string][]string, len(nodeSet))
 	for cluster, nodes := range nodeSet {
-		// Convert map keys to slice
 		list := make([]string, 0, len(nodes))
 		for node := range nodes {
 			list = append(list, node)
 		}
-		// set.Strings sorts the slice and ensures uniqueness
+		sort.Strings(list)
-		nodeList[cluster] = set.Strings(list)
+		nodeList[cluster] = list
 	}
 
-	return nodeList
+	return nodeList, nil
 }