diff --git a/lib/wal/main_test.go b/lib/wal/main_test.go
new file mode 100644
index 0000000..2e11436
--- /dev/null
+++ b/lib/wal/main_test.go
@@ -0,0 +1,11 @@
+package wal
+
+import (
+	"testing"
+
+	"go.uber.org/goleak"
+)
+
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m)
+}
diff --git a/mdb/db-primary.go b/mdb/db-primary.go
new file mode 100644
index 0000000..df6ba5b
--- /dev/null
+++ b/mdb/db-primary.go
@@ -0,0 +1,67 @@
+package mdb
+
+/*
+func (db *Database) openPrimary() (err error) {
+	wal, err := cwal.Open(db.walRootDir, cwal.Config{
+		SegMinCount:  db.conf.WALSegMinCount,
+		SegMaxAgeSec: db.conf.WALSegMaxAgeSec,
+	})
+
+	pFile, err := pfile.Open(db.pageFilePath,
+
+	pFile, err := openPageFileAndReplayWAL(db.rootDir)
+	if err != nil {
+		return err
+	}
+	defer pFile.Close()
+
+	pfHeader, err := pFile.ReadHeader()
+	if err != nil {
+		return err
+	}
+
+	tx := db.Snapshot()
+	tx.seqNum = pfHeader.SeqNum
+	tx.updatedAt = pfHeader.UpdatedAt
+
+	pIndex, err := pagefile.NewIndex(pFile)
+	if err != nil {
+		return err
+	}
+
+	err = pFile.IterateAllocated(pIndex, func(cID, iID uint64, data []byte) error {
+		return db.loadItem(tx, cID, iID, data)
+	})
+	if err != nil {
+		return err
+	}
+
+	w, err := cwal.OpenWriter(db.walRootDir, &cwal.WriterConfig{
+		SegMinCount:  db.conf.WALSegMinCount,
+		SegMaxAgeSec: db.conf.WALSegMaxAgeSec,
+	})
+	if err != nil {
+		return err
+	}
+
+	db.done.Add(1)
+	go txAggregator{
+		Stop:     db.stop,
+		Done:     db.done,
+		ModChan:  db.modChan,
+		W:        w,
+		Index:    pIndex,
+		Snapshot: db.snapshot,
+	}.Run()
+
+	db.done.Add(1)
+	go (&fileWriter{
+		Stop:         db.stop,
+		Done:         db.done,
+		PageFilePath: db.pageFilePath,
+		WALRootDir:   db.walRootDir,
+	}).Run()
+
+	return nil
+}
+*/
diff --git a/mdb/db-secondary.go b/mdb/db-secondary.go
new file mode 100644
index 0000000..f03b01f
--- /dev/null
+++ b/mdb/db-secondary.go
@@ -0,0 +1,129 @@
+package mdb
+
+/*
+func (db *Database) openSecondary() (err error) {
+	if db.shouldLoadFromPrimary() {
+		if err := db.loadFromPrimary(); err != nil {
+			return err
+		}
+	}
+
+	log.Printf("Opening page-file...")
+
+	pFile, err := openPageFileAndReplayWAL(db.rootDir)
+	if err != nil {
+		return err
+	}
+	defer pFile.Close()
+
+	pfHeader, err := pFile.ReadHeader()
+	if err != nil {
+		return err
+	}
+
+	log.Printf("Building page-file index...")
+
+	pIndex, err := pagefile.NewIndex(pFile)
+	if err != nil {
+		return err
+	}
+
+	tx := db.Snapshot()
+	tx.seqNum = pfHeader.SeqNum
+	tx.updatedAt = pfHeader.UpdatedAt
+
+	log.Printf("Loading data into memory...")
+
+	err = pFile.IterateAllocated(pIndex, func(cID, iID uint64, data []byte) error {
+		return db.loadItem(tx, cID, iID, data)
+	})
+	if err != nil {
+		return err
+	}
+
+	log.Printf("Creating writer...")
+
+	w, err := cswal.OpenWriter(db.walRootDir, &cswal.WriterConfig{
+		SegMinCount:  db.conf.WALSegMinCount,
+		SegMaxAgeSec: db.conf.WALSegMaxAgeSec,
+	})
+	if err != nil {
+		return err
+	}
+
+	db.done.Add(1)
+	go (&walFollower{
+		Stop:   db.stop,
+		Done:   db.done,
+		W:      w,
+		Client: NewClient(db.conf.PrimaryURL, db.conf.ReplicationPSK, db.conf.NetTimeout),
+	}).Run()
+
+	db.done.Add(1)
+	go (&follower{
+		Stop:         db.stop,
+		Done:         db.done,
+		WALRootDir:   db.walRootDir,
+		SeqNum:       pfHeader.SeqNum,
+		ApplyChanges: db.applyChanges,
+	}).Run()
+
+	db.done.Add(1)
+	go (&fileWriter{
+		Stop:         db.stop,
+		Done:         db.done,
+		PageFilePath: db.pageFilePath,
+		WALRootDir:   db.walRootDir,
+	}).Run()
+
+	return nil
+}
+
+func (db *Database) shouldLoadFromPrimary() bool {
+	if _, err := os.Stat(db.walRootDir); os.IsNotExist(err) {
+		log.Printf("WAL doesn't exist.")
+		return true
+	}
+	if _, err := os.Stat(db.pageFilePath); os.IsNotExist(err) {
+		log.Printf("Page-file doesn't exist.")
+		return true
+	}
+	return false
+}
+
+func (db *Database) loadFromPrimary() error {
+	client := NewClient(db.conf.PrimaryURL, db.conf.ReplicationPSK, db.conf.NetTimeout)
+	defer client.Disconnect()
+
+	log.Printf("Loading data from primary...")
+
+	if err := os.RemoveAll(db.pageFilePath); err != nil {
+		log.Printf("Failed to remove page-file: %s", err)
+		return errs.IO.WithErr(err) // Caller can retry.
+	}
+
+	if err := os.RemoveAll(db.walRootDir); err != nil {
+		log.Printf("Failed to remove WAL: %s", err)
+		return errs.IO.WithErr(err) // Caller can retry.
+	}
+
+	err := client.DownloadPageFile(db.pageFilePath+".tmp", db.pageFilePath)
+	if err != nil {
+		log.Printf("Failed to get page-file from primary: %s", err)
+		return err // Caller can retry.
+	}
+
+	pfHeader, err := pagefile.ReadHeader(db.pageFilePath)
+	if err != nil {
+		log.Printf("Failed to read page-file sequence number: %s", err)
+		return err // Caller can retry.
+	}
+
+	if err = cswal.CreateEx(db.walRootDir, pfHeader.SeqNum+1); err != nil {
+		log.Printf("Failed to initialize WAL: %s", err)
+		return err // Caller can retry.
+	}
+
+	return nil
+}
+*/
diff --git a/mdb/db-testlist_test.go b/mdb/db-testlist_test.go
new file mode 100644
index 0000000..008093a
--- /dev/null
+++ b/mdb/db-testlist_test.go
@@ -0,0 +1,138 @@
+package mdb
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+)
+
+func TestDBList(t *testing.T) {
+	db := NewTestDBPrimary(t, t.TempDir())
+
+	var (
+		user1 = User{
+			ID:    NewID(),
+			Name:  "User1",
+			Email: "user1@gmail.com",
+		}
+
+		user2 = User{
+			ID:    NewID(),
+			Name:  "User2",
+			Email: "user2@gmail.com",
+		}
+
+		user3 = User{
+			ID:    NewID(),
+			Name:  "User3",
+			Email: "user3@gmail.com",
+		}
+		user1Data = make([]UserDataItem, 10)
+		user2Data = make([]UserDataItem, 4)
+		user3Data = make([]UserDataItem, 8)
+	)
+
+	err := db.Update(func(tx *Snapshot) error {
+		if err := db.Users.Insert(tx, &user1); err != nil {
+			return err
+		}
+
+		if err := db.Users.Insert(tx, &user2); err != nil {
+			return err
+		}
+
+		for i := range user1Data {
+			user1Data[i] = UserDataItem{
+				ID:     NewID(),
+				UserID: user1.ID,
+				Name:   fmt.Sprintf("Name1: %d", i),
+				Data:   fmt.Sprintf("Data: %d", i),
+			}
+
+			if err := db.UserData.Insert(tx, &user1Data[i]); err != nil {
+				return err
+			}
+		}
+
+		for i := range user2Data {
+			user2Data[i] = UserDataItem{
+				ID:     NewID(),
+				UserID: user2.ID,
+				Name:   fmt.Sprintf("Name2: %d", i),
+				Data:   fmt.Sprintf("Data: %d", i),
+			}
+
+			if err := db.UserData.Insert(tx, &user2Data[i]); err != nil {
+				return err
+			}
+		}
+
+		for i := range user3Data {
+			user3Data[i] = UserDataItem{
+				ID:     NewID(),
+				UserID: user3.ID,
+				Name:   fmt.Sprintf("Name3: %d", i),
+				Data:   fmt.Sprintf("Data: %d", i),
+			}
+
+			if err := db.UserData.Insert(tx, &user3Data[i]); err != nil {
+				return err
+			}
+		}
+
+		return nil
+	})
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	type TestCase struct {
+		Name     string
+		Args     ListArgs[UserDataItem]
+		Expected []UserDataItem
+	}
+
+	cases := []TestCase{
+		{
+			Name: "User1 all",
+			Args: ListArgs[UserDataItem]{
+				After: &UserDataItem{
+					UserID: user1.ID,
+				},
+				While: func(item *UserDataItem) bool {
+					return item.UserID == user1.ID
+				},
+			},
+			Expected: user1Data,
+		}, {
+			Name: "User1 limited",
+			Args: ListArgs[UserDataItem]{
+				After: &UserDataItem{
+					UserID: user1.ID,
+				},
+				While: func(item *UserDataItem) bool {
+					return item.UserID == user1.ID
+				},
+				Limit: 4,
+			},
+			Expected: user1Data[:4],
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.Name, func(t *testing.T) {
+			tx := db.Snapshot()
+			l := db.UserData.ByName.List(tx, tc.Args, nil)
+			if len(l) != len(tc.Expected) {
+				t.Fatal(tc.Name, l)
+			}
+
+			for i := range l {
+				if !reflect.DeepEqual(*l[i], tc.Expected[i]) {
+					t.Fatal(tc.Name, l)
+				}
+			}
+		})
+	}
+}
diff --git a/mdb/main_test.go b/mdb/main_test.go
new file mode 100644
index 0000000..d9e09aa
--- /dev/null
+++ b/mdb/main_test.go
@@ -0,0 +1,11 @@
+package mdb
+
+import (
+	"testing"
+
+	"go.uber.org/goleak"
+)
+
+func TestMain(m *testing.M) {
+	goleak.VerifyTestMain(m)
+}
diff --git a/mdb/txaggregator.go b/mdb/txaggregator.go
new file mode 100644
index 0000000..e073e1f
--- /dev/null
+++ b/mdb/txaggregator.go
@@ -0,0 +1,92 @@
+package mdb
+
+/*
+type txAggregator struct {
+	Stop     chan struct{}
+	Done     *sync.WaitGroup
+	ModChan  chan txMod
+	W        *cswal.Writer
+	Index    *pagefile.Index
+	Snapshot *atomic.Pointer[Snapshot]
+}
+
+func (p txAggregator) Run() {
+	defer p.Done.Done()
+	defer p.W.Close()
+
+	var (
+		tx       *Snapshot
+		mod      txMod
+		rec      cswal.Record
+		err      error
+		toNotify = make([]chan error, 0, 1024)
+	)
+
+READ_FIRST:
+
+	toNotify = toNotify[:0]
+
+	select {
+	case mod = <-p.ModChan:
+		goto BEGIN
+	case <-p.Stop:
+		goto END
+	}
+
+BEGIN:
+
+	tx = p.Snapshot.Load().begin()
+	goto APPLY_MOD
+
+CLONE:
+
+	tx = tx.clone()
+	goto APPLY_MOD
+
+APPLY_MOD:
+
+	if err = mod.Update(tx); err != nil {
+		mod.Resp <- err
+		goto ROLLBACK
+	}
+
+	toNotify = append(toNotify, mod.Resp)
+	goto NEXT
+
+ROLLBACK:
+
+	if len(toNotify) == 0 {
+		goto READ_FIRST
+	}
+
+	tx = tx.rollback()
+	goto NEXT
+
+NEXT:
+
+	select {
+	case mod = <-p.ModChan:
+		goto CLONE
+	default:
+		goto WRITE
+	}
+
+WRITE:
+
+	rec, err = writeChangesToWAL(tx.changes, p.Index, p.W)
+	if err == nil {
+		tx.seqNum = rec.SeqNum
+		tx.updatedAt = rec.CreatedAt
+		tx.setReadOnly()
+		p.Snapshot.Store(tx)
+	}
+
+	for i := range toNotify {
+		toNotify[i] <- err
+	}
+
+	goto READ_FIRST
+
+END:
+}
+*/