[Feature] add auto merge background task

db.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/bwmarrin/snowflake"
 	"github.com/gofrs/flock"
+	"github.com/robfig/cron/v3"
 	"github.com/rosedblabs/rosedb/v2/index"
 	"github.com/rosedblabs/rosedb/v2/utils"
 	"github.com/rosedblabs/wal"
@@ -52,7 +53,8 @@ type DB struct {
 	encodeHeader     []byte
 	watchCh          chan *Event // user consume channel for watch events
 	watcher          *Watcher
-	expiredCursorKey []byte // the location to which DeleteExpiredKeys executes.
+	expiredCursorKey []byte     // the location to which DeleteExpiredKeys executes.
+	cronScheduler    *cron.Cron // cron scheduler for auto merge task
 }
 
 // Stat represents the statistics of the database.
@@ -127,6 +129,17 @@ func Open(options Options) (*DB, error) {
 		go db.watcher.sendEvent(db.watchCh)
 	}
 
+	if len(options.AutoMergeCronExpr) > 0 {
+		db.cronScheduler = cron.New(cron.WithParser(
+			cron.NewParser(cron.SecondOptional | cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor)))
+		db.cronScheduler.AddFunc(options.AutoMergeCronExpr, func() {
+			// maybe we should deal with different errors with different logic, but a background task can't omit its error.
+			// after auto merge, we should close and reopen the db.
+			_ = db.Merge(true)
+		})
+		db.cronScheduler.Start()
+	}
+
 	return db, nil
 }
 
@@ -179,6 +192,11 @@ func (db *DB) Close() error {
 		close(db.watchCh)
 	}
 
+	// close auto merge cron scheduler
+	if db.cronScheduler != nil {
+		db.cronScheduler.Stop()
+	}
+
 	db.closed = true
 	return nil
 }
@@ -552,6 +570,14 @@ func checkOptions(options Options) error {
 	if options.SegmentSize <= 0 {
 		return errors.New("database data file size must be greater than 0")
 	}
+
+	if len(options.AutoMergeCronExpr) > 0 {
+		if _, err := cron.NewParser(cron.SecondOptional | cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor).
+			Parse(options.AutoMergeCronExpr); err != nil {
+			return fmt.Errorf("databse auto merge cron expression is invalid, err: %s", err)
+		}
+	}
+
 	return nil
 }
 

db_test.go

@@ -1,7 +1,10 @@
 package rosedb
 
 import (
+	"errors"
+	"io"
 	"math/rand"
+	"os"
 	"sync"
 	"testing"
 	"time"
@@ -704,3 +707,105 @@ func TestDB_Persist(t *testing.T) {
 	assert.Nil(t, err)
 	assert.NotNil(t, val2)
 }
+
+func TestDB_Invalid_Cron_Expression(t *testing.T) {
+	options := DefaultOptions
+	options.AutoMergeCronExpr = "*/1 * * * * * *"
+	_, err := Open(options)
+	assert.NotNil(t, err)
+}
+
+func TestDB_Valid_Cron_Expression(t *testing.T) {
+	options := DefaultOptions
+	{
+		options.AutoMergeCronExpr = "* */1 * * * *"
+		db, err := Open(options)
+		assert.Nil(t, err)
+		destroyDB(db)
+	}
+
+	{
+		options.AutoMergeCronExpr = "*/1 * * * *"
+		db, err := Open(options)
+		assert.Nil(t, err)
+		destroyDB(db)
+	}
+
+	{
+		options.AutoMergeCronExpr = "5 0 * 8 *"
+		db, err := Open(options)
+		assert.Nil(t, err)
+		destroyDB(db)
+	}
+
+	{
+		options.AutoMergeCronExpr = "*/2 14 1 * *"
+		db, err := Open(options)
+		assert.Nil(t, err)
+		destroyDB(db)
+	}
+
+	{
+		options.AutoMergeCronExpr = "@hourly"
+		db, err := Open(options)
+		assert.Nil(t, err)
+		destroyDB(db)
+	}
+}
+
+func TestDB_Auto_Merge(t *testing.T) {
+	options := DefaultOptions
+	db, err := Open(options)
+	assert.Nil(t, err)
+	defer destroyDB(db)
+
+	for i := 0; i < 2000; i++ {
+		delKey := utils.GetTestKey(rand.Int())
+		err := db.Put(delKey, utils.RandomValue(128))
+		assert.Nil(t, err)
+		err = db.Put(utils.GetTestKey(rand.Int()), utils.RandomValue(2*KB))
+		assert.Nil(t, err)
+		err = db.Delete(delKey)
+		assert.Nil(t, err)
+	}
+
+	{
+		reader := db.dataFiles.NewReader()
+		var keyCnt int
+		for {
+			if _, _, err := reader.Next(); errors.Is(err, io.EOF) {
+				break
+			}
+			keyCnt++
+		}
+		// each record has one data wal and commit at end of batch with wal
+		// so totally is 2000 * 3 * 2 = 12000
+		assert.Equal(t, 12000, keyCnt)
+	}
+
+	mergeDirPath := mergeDirPath(options.DirPath)
+	if _, err := os.Stat(mergeDirPath); err != nil {
+		assert.True(t, os.IsNotExist(err))
+	}
+	assert.NoError(t, db.Close())
+
+	{
+		options.AutoMergeCronExpr = "* * * * * *" // every second
+		db, err := Open(options)
+		assert.Nil(t, err)
+		{
+			<-time.After(time.Second * 2)
+			reader := db.dataFiles.NewReader()
+			var keyCnt int
+			for {
+				if _, _, err := reader.Next(); errors.Is(err, io.EOF) {
+					break
+				}
+				keyCnt++
+			}
+			// after merge records are only valid data, so totally is 2000
+			assert.Equal(t, 2000, keyCnt)
+		}
+		destroyDB(db)
+	}
+}

go.mod

@@ -12,6 +12,7 @@ require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/kr/text v0.2.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/robfig/cron/v3 v3.0.0 // indirect
 	golang.org/x/sys v0.11.0 // indirect
 	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect

go.sum

@@ -17,6 +17,8 @@ github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/robfig/cron/v3 v3.0.0 h1:kQ6Cb7aHOHTSzNVNEhmp8EcWKLb4CbiMW9h9VyIhO4E=
+github.com/robfig/cron/v3 v3.0.0/go.mod h1:eQICP3HwyT7UooqI/z+Ov+PtYAWygg1TEWWzGIFLtro=
 github.com/rosedblabs/wal v1.3.6-0.20230924022528-3202245af020 h1:EA8XGCVg1FDM6Dh4MP4sTsmH3gvjhRtp/N+lbnBwtJE=
 github.com/rosedblabs/wal v1.3.6-0.20230924022528-3202245af020/go.mod h1:wdq54KJUyVTOv1uddMc6Cdh2d/YCIo8yjcwJAb1RCEM=
 github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=

options.go

@@ -31,6 +31,17 @@ type Options struct {
 	// WatchQueueSize the cache length of the watch queue.
 	// if the size greater than 0, which means enable the watch.
 	WatchQueueSize uint64
+
+	// AutoMergeEnable enable the auto merge.
+	// auto merge will be triggered when cron expr is satisfied.
+	// cron expression follows the standard cron expression.
+	// e.g. "0 0 * * *" means merge at 00:00:00 every day.
+	// it also supports seconds optionally.
+	// when enable the second field, the cron expression will be like this: "0/10 * * * * *" (every 10 seconds).
+	// when auto merge is enabled, the db will be closed and reopened after merge done.
+	// do not set this shecule too frequently, it will affect the performance.
+	// refer to https://en.wikipedia.org/wiki/Cron
+	AutoMergeCronExpr string
 }
 
 // BatchOptions specifies the options for creating a batch.
@@ -49,12 +60,13 @@ const (
 )
 
 var DefaultOptions = Options{
-	DirPath:        tempDBDir(),
-	SegmentSize:    1 * GB,
-	BlockCache:     0,
-	Sync:           false,
-	BytesPerSync:   0,
-	WatchQueueSize: 0,
+	DirPath:           tempDBDir(),
+	SegmentSize:       1 * GB,
+	BlockCache:        0,
+	Sync:              false,
+	BytesPerSync:      0,
+	WatchQueueSize:    0,
+	AutoMergeCronExpr: "",
 }
 
 var DefaultBatchOptions = BatchOptions{