chore: reduce database writes (#24672)

server/db/settings/setting.go

@@ -11,11 +11,11 @@ import (
 	"strconv"
 	"strings"
 	"sync"
-	"sync/atomic"
 	"time"
 
 	"github.com/evcc-io/evcc/server/db"
 	"github.com/evcc-io/evcc/util"
+	"github.com/samber/lo"
 	"go.yaml.in/yaml/v4"
 )
 
@@ -23,6 +23,7 @@ var ErrNotFound = errors.New("not found")
 
 // setting is a settings entry
 type setting struct {
+	dirty bool
 	Key   string `json:"key" gorm:"primarykey"`
 	Value string `json:"value"`
 }
@@ -30,7 +31,6 @@ type setting struct {
 var (
 	mu       sync.RWMutex
 	settings []setting
-	dirty    int32
 )
 
 func Init() error {
@@ -42,12 +42,22 @@ func Init() error {
 }
 
 func Persist() error {
-	dirty := atomic.CompareAndSwapInt32(&dirty, 1, 0)
-	if !dirty || len(settings) == 0 {
-		// avoid "empty slice found"
-		return nil
+	mu.Lock()
+	defer mu.Unlock()
+
+	if dirty := lo.FilterMap(settings, func(s setting, _ int) (*setting, bool) {
+		return &s, s.dirty
+	}); len(dirty) > 0 {
+		if err := db.Instance.Save(dirty).Error; err != nil {
+			return err
+		}
+
+		for _, s := range dirty {
+			s.dirty = false
+		}
 	}
-	return db.Instance.Save(settings).Error
+
+	return nil
 }
 
 func All() []setting {
@@ -88,14 +98,11 @@ func SetString(key string, val string) {
 	mu.Lock()
 	defer mu.Unlock()
 
-	idx := slices.IndexFunc(settings, equal(key))
-
-	if idx < 0 {
-		settings = append(settings, setting{key, val})
-		atomic.StoreInt32(&dirty, 1)
+	if idx := slices.IndexFunc(settings, equal(key)); idx < 0 {
+		settings = append(settings, setting{true, key, val})
 	} else if settings[idx].Value != val {
+		settings[idx].dirty = true
 		settings[idx].Value = val
-		atomic.StoreInt32(&dirty, 1)
 	}
 }
 
@@ -170,7 +177,7 @@ func Float(key string) (float64, error) {
 func Time(key string) (time.Time, error) {
 	s, err := String(key)
 	if err != nil {
-		return time.Now(), err
+		return time.Time{}, err
 	}
 	return time.Parse(time.RFC3339, s)
 }