iterfunc experiment

Co-authored-by: jdl <jdl@desktop>
Reviewed-on: #2

README.md

@@ -4,6 +4,7 @@ Replicated in-memory database and file store.
 
 ## TODO
 
+* [ ] mdb: Tests for using `nil` snapshots ?
 * [ ] mdb: tests for sanitize and validate functions
 * [ ] Test: lib/wal iterator w/ corrupt file (random corruptions)
 * [ ] Test: lib/wal io.go

go.mod

@@ -1,6 +1,6 @@
 module git.crumpington.com/public/jldb
 
-go 1.21.1
+go 1.22
 
 require (
 	github.com/google/btree v1.1.2

lib/errs/error.go

@@ -8,26 +8,27 @@ import (
 )
 
 type Error struct {
-	msg        string
-	code       int64
+	Code       int64
+	Msg        string
+	StackTrace string
+
 	collection string
 	index      string
-	stackTrace string
 	err        error // Wrapped error
 }
 
 func NewErr(code int64, msg string) *Error {
 	return &Error{
-		msg:  msg,
-		code: code,
+		Code: code,
+		Msg:  msg,
 	}
 }
 
 func (e *Error) Error() string {
 	if e.collection != "" || e.index != "" {
-		return fmt.Sprintf(`[%d] (%s/%s) %s`, e.code, e.collection, e.index, e.msg)
+		return fmt.Sprintf(`[%d] (%s/%s) %s`, e.Code, e.collection, e.index, e.Msg)
 	} else {
-		return fmt.Sprintf("[%d] %s", e.code, e.msg)
+		return fmt.Sprintf("[%d] %s", e.Code, e.Msg)
 	}
 }
 
@@ -36,11 +37,15 @@ func (e *Error) Is(rhs error) bool {
 	if !ok {
 		return false
 	}
-	return e.code == e2.code
+	return e.Code == e2.Code
+}
+
+func (e *Error) Unwrap() error {
+	return e.err
 }
 
 func (e *Error) WithErr(err error) *Error {
-	if e2, ok := err.(*Error); ok && e2.code == e.code {
+	if e2, ok := err.(*Error); ok && e2.Code == e.Code {
 		return e2
 	}
 
@@ -49,18 +54,11 @@ func (e *Error) WithErr(err error) *Error {
 	return e2
 }
 
-func (e *Error) Unwrap() error {
-	if e.err != nil {
-		return e.err
-	}
-	return e
-}
-
 func (e *Error) WithMsg(msg string, args ...any) *Error {
 	err := *e
-	err.msg += ": " + fmt.Sprintf(msg, args...)
-	if len(err.stackTrace) == 0 {
-		err.stackTrace = string(debug.Stack())
+	err.Msg += ": " + fmt.Sprintf(msg, args...)
+	if len(err.StackTrace) == 0 {
+		err.StackTrace = string(debug.Stack())
 	}
 	return &err
 }
@@ -78,16 +76,16 @@ func (e *Error) WithIndex(s string) *Error {
 }
 
 func (e *Error) msgTruncacted() string {
-	if len(e.msg) > 255 {
-		return e.msg[:255]
+	if len(e.Msg) > 255 {
+		return e.Msg[:255]
 	}
-	return e.msg
+	return e.Msg
 }
 
 func (e *Error) Write(w io.Writer) error {
 	msg := e.msgTruncacted()
 
-	if err := binary.Write(w, binary.LittleEndian, e.code); err != nil {
+	if err := binary.Write(w, binary.LittleEndian, e.Code); err != nil {
 		return IO.WithErr(err)
 	}
 
@@ -103,7 +101,7 @@ func (e *Error) Read(r io.Reader) error {
 		size uint8
 	)
 
-	if err := binary.Read(r, binary.LittleEndian, &e.code); err != nil {
+	if err := binary.Read(r, binary.LittleEndian, &e.Code); err != nil {
 		return IO.WithErr(err)
 	}
 
@@ -116,6 +114,6 @@ func (e *Error) Read(r io.Reader) error {
 		return IO.WithErr(err)
 	}
 
-	e.msg = string(msgBuf)
+	e.Msg = string(msgBuf)
 	return nil
 }

lib/errs/fmt.go

@@ -10,12 +10,12 @@ func FmtDetails(err error) string {
 
 	var s string
 	if e.collection != "" || e.index != "" {
-		s = fmt.Sprintf(`[%d] (%s/%s) %s`, e.code, e.collection, e.index, e.msg)
+		s = fmt.Sprintf(`[%d] (%s/%s) %s`, e.Code, e.collection, e.index, e.Msg)
 	} else {
-		s = fmt.Sprintf("[%d] %s", e.code, e.msg)
+		s = fmt.Sprintf("[%d] %s", e.Code, e.Msg)
 	}
-	if len(e.stackTrace) != 0 {
-		s += "\n\nStack Trace:\n" + e.stackTrace + "\n"
+	if len(e.StackTrace) != 0 {
+		s += "\n\nStack Trace:\n" + e.StackTrace + "\n"
 	}
 
 	return s

lib/rep/http-handler.go

@@ -12,6 +12,7 @@ const (
 	pathStreamWAL = "stream-wal"
 )
 
+// TODO: Remove this!
 func (rep *Replicator) Handle(w http.ResponseWriter, r *http.Request) {
 	// We'll handle two types of requests: HTTP GET requests for JSON, or
 	// streaming requets for state or wall.

lib/rep/replicator-walgc.go

@@ -15,7 +15,7 @@ func (rep *Replicator) runWALGC() {
 		select {
 		case <-ticker.C:
 			state := rep.getState()
-			before := time.Now().Unix() - rep.conf.WALSegMaxAgeSec
+			before := time.Now().Unix() - rep.conf.WALSegGCAgeSec
 			if err := rep.wal.DeleteBefore(before, state.SeqNum); err != nil {
 				log.Printf("[WAL-GC] failed to delete wal segments: %v", err)
 			}

lib/rep/replicator.go

@@ -2,6 +2,7 @@ package rep
 
 import (
 	"io"
+	"log"
 	"net"
 	"os"
 	"sync"
@@ -94,41 +95,49 @@ func Open(app App, conf Config) (*Replicator, error) {
 	rep.client = newClient(rep.conf.PrimaryEndpoint, rep.conf.ReplicationPSK, rep.conf.NetTimeout)
 
 	if err := rep.initDirectories(); err != nil {
+		log.Printf("Failed to init directories: %v", err)
 		return nil, err
 	}
 
 	if err := rep.acquireLock(); err != nil {
 		rep.Close()
+		log.Printf("Failed to acquire lock: %v", err)
 		return nil, err
 	}
 
 	if err := rep.loadLocalState(); err != nil {
 		rep.Close()
+		log.Printf("Failed to load local state: %v", err)
 		return nil, err
 	}
 
 	if err := rep.openWAL(); err != nil {
 		rep.Close()
+		log.Printf("Failed to open WAL: %v", err)
 		return nil, err
 	}
 
 	if err := rep.recvStateIfNecessary(); err != nil {
 		rep.Close()
+		log.Printf("Failed to recv state: %v", err)
 		return nil, err
 	}
 
 	if err := rep.app.InitStorage(); err != nil {
 		rep.Close()
+		log.Printf("Failed to init storage: %v", err)
 		return nil, err
 	}
 
 	if err := rep.replay(); err != nil {
 		rep.Close()
+		log.Printf("Failed to replay: %v", err)
 		return nil, err
 	}
 
 	if err := rep.app.LoadFromStorage(); err != nil {
 		rep.Close()
+		log.Printf("Failed to load from storage: %v", err)
 		return nil, err
 	}
 

mdb/collection.go

@@ -21,10 +21,10 @@ type Collection[T any] struct {
 	sanitize func(*T)
 	validate func(*T) error
 
-	indices       []Index[T]
-	uniqueIndices []Index[T]
+	indices       []*Index[T]
+	uniqueIndices []*Index[T]
 
-	ByID Index[T]
+	ByID *Index[T]
 
 	buf *bytes.Buffer
 }
@@ -65,8 +65,8 @@ func NewCollection[T any](db *Database, name string, conf *CollectionConfig[T])
 		copy:          conf.Copy,
 		sanitize:      conf.Sanitize,
 		validate:      conf.Validate,
-		indices:       []Index[T]{},
-		uniqueIndices: []Index[T]{},
+		indices:       []*Index[T]{},
+		uniqueIndices: []*Index[T]{},
 		buf:           &bytes.Buffer{},
 	}
 
@@ -92,7 +92,7 @@ func NewCollection[T any](db *Database, name string, conf *CollectionConfig[T])
 	return c
 }
 
-func (c Collection[T]) Name() string {
+func (c *Collection[T]) Name() string {
 	return c.name
 }
 
@@ -108,35 +108,8 @@ type indexConfig[T any] struct {
 	Include func(item *T) bool
 }
 
-func (c Collection[T]) Get(tx *Snapshot, id uint64) (*T, bool) {
-	x := new(T)
-	c.setID(x, id)
-	return c.ByID.Get(tx, x)
-}
-
-func (c Collection[T]) List(tx *Snapshot, ids []uint64, out []*T) []*T {
-	if len(ids) == 0 {
-		return out[:0]
-	}
-
-	if cap(out) < len(ids) {
-		out = make([]*T, len(ids))
-	}
-	out = out[:0]
-
-	for _, id := range ids {
-		item, ok := c.Get(tx, id)
-		if ok {
-			out = append(out, item)
-		}
-	}
-
-	return out
-}
-
 // AddIndex: Add an index to the collection.
-func (c *Collection[T]) addIndex(conf indexConfig[T]) Index[T] {
-
+func (c *Collection[T]) addIndex(conf indexConfig[T]) *Index[T] {
 	var less func(*T, *T) bool
 
 	if conf.Unique {
@@ -160,7 +133,8 @@ func (c *Collection[T]) addIndex(conf indexConfig[T]) Index[T] {
 		BTree: btree.NewG(256, less),
 	}
 
-	index := Index[T]{
+	index := &Index[T]{
+		db:           c.db,
 		collectionID: c.collectionID,
 		name:         conf.Name,
 		indexID:      c.getState(c.db.Snapshot()).addIndex(indexState),
@@ -176,7 +150,35 @@ func (c *Collection[T]) addIndex(conf indexConfig[T]) Index[T] {
 	return index
 }
 
-func (c Collection[T]) Insert(tx *Snapshot, userItem *T) error {
+func (c *Collection[T]) Get(tx *Snapshot, id uint64) *T {
+	if tx == nil {
+		tx = c.db.Snapshot()
+	}
+	item := new(T)
+	c.setID(item, id)
+	return c.ByID.Get(tx, item)
+}
+
+func (c *Collection[T]) Has(tx *Snapshot, id uint64) bool {
+	if tx == nil {
+		tx = c.db.Snapshot()
+	}
+	item := new(T)
+	c.setID(item, id)
+	return c.ByID.Has(tx, item)
+}
+
+func (c *Collection[T]) Insert(tx *Snapshot, userItem *T) error {
+	if tx == nil {
+		return c.db.Update(func(tx *Snapshot) error {
+			return c.insert(tx, userItem)
+		})
+	}
+
+	return c.insert(tx, userItem)
+}
+
+func (c *Collection[T]) insert(tx *Snapshot, userItem *T) error {
 	if err := c.ensureMutable(tx); err != nil {
 		return err
 	}
@@ -203,7 +205,16 @@ func (c Collection[T]) Insert(tx *Snapshot, userItem *T) error {
 	return nil
 }
 
-func (c Collection[T]) Update(tx *Snapshot, userItem *T) error {
+func (c *Collection[T]) Update(tx *Snapshot, userItem *T) error {
+	if tx == nil {
+		return c.db.Update(func(tx *Snapshot) error {
+			return c.update(tx, userItem)
+		})
+	}
+	return c.update(tx, userItem)
+}
+
+func (c *Collection[T]) update(tx *Snapshot, userItem *T) error {
 	if err := c.ensureMutable(tx); err != nil {
 		return err
 	}
@@ -235,7 +246,37 @@ func (c Collection[T]) Update(tx *Snapshot, userItem *T) error {
 	return nil
 }
 
-func (c Collection[T]) Upsert(tx *Snapshot, item *T) error {
+func (c *Collection[T]) UpdateFunc(tx *Snapshot, id uint64, update func(item *T) error) error {
+	if tx == nil {
+		return c.db.Update(func(tx *Snapshot) error {
+			return c.updateFunc(tx, id, update)
+		})
+	}
+	return c.updateFunc(tx, id, update)
+}
+
+func (c *Collection[T]) updateFunc(tx *Snapshot, id uint64, update func(item *T) error) error {
+	item := c.Get(tx, id)
+	if item == nil {
+		return errs.NotFound
+	}
+	if err := update(item); err != nil {
+		return err
+	}
+	c.setID(item, id) // Don't allow the ID to change.
+	return c.update(tx, item)
+}
+
+func (c *Collection[T]) Upsert(tx *Snapshot, item *T) error {
+	if tx == nil {
+		return c.db.Update(func(tx *Snapshot) error {
+			return c.upsert(tx, item)
+		})
+	}
+	return c.upsert(tx, item)
+}
+
+func (c *Collection[T]) upsert(tx *Snapshot, item *T) error {
 	err := c.Insert(tx, item)
 	if err == nil {
 		return nil
@@ -246,7 +287,46 @@ func (c Collection[T]) Upsert(tx *Snapshot, item *T) error {
 	return err
 }
 
-func (c Collection[T]) Delete(tx *Snapshot, itemID uint64) error {
+func (c *Collection[T]) UpsertFunc(tx *Snapshot, id uint64, update func(item *T) error) error {
+	if tx == nil {
+		c.db.Update(func(tx *Snapshot) error {
+			return c.upsertFunc(tx, id, update)
+		})
+	}
+	return c.upsertFunc(tx, id, update)
+}
+
+func (c *Collection[T]) upsertFunc(tx *Snapshot, id uint64, update func(item *T) error) error {
+	insert := false
+
+	item := c.Get(tx, id)
+	if item == nil {
+		item = new(T)
+		insert = true
+	}
+
+	if err := update(item); err != nil {
+		return err
+	}
+
+	c.setID(item, id) // Don't allow the ID to change.
+
+	if insert {
+		return c.insert(tx, item)
+	}
+	return c.update(tx, item)
+}
+
+func (c *Collection[T]) Delete(tx *Snapshot, itemID uint64) error {
+	if tx == nil {
+		return c.db.Update(func(tx *Snapshot) error {
+			return c.delete(tx, itemID)
+		})
+	}
+	return c.delete(tx, itemID)
+}
+
+func (c *Collection[T]) delete(tx *Snapshot, itemID uint64) error {
 	if err := c.ensureMutable(tx); err != nil {
 		return err
 	}
@@ -254,13 +334,20 @@ func (c Collection[T]) Delete(tx *Snapshot, itemID uint64) error {
 	return c.deleteItem(tx, itemID)
 }
 
-func (c Collection[T]) getByID(tx *Snapshot, itemID uint64) (*T, bool) {
+func (c *Collection[T]) Count(tx *Snapshot) int {
+	if tx == nil {
+		tx = c.db.Snapshot()
+	}
+	return c.ByID.Count(tx)
+}
+
+func (c *Collection[T]) getByID(tx *Snapshot, itemID uint64) (*T, bool) {
 	x := new(T)
 	c.setID(x, itemID)
 	return c.ByID.get(tx, x)
 }
 
-func (c Collection[T]) ensureMutable(tx *Snapshot) error {
+func (c *Collection[T]) ensureMutable(tx *Snapshot) error {
 	if !tx.writable() {
 		return errs.ReadOnly
 	}
@@ -274,7 +361,7 @@ func (c Collection[T]) ensureMutable(tx *Snapshot) error {
 }
 
 // For initial data loading.
-func (c Collection[T]) insertItem(tx *Snapshot, itemID uint64, data []byte) error {
+func (c *Collection[T]) insertItem(tx *Snapshot, itemID uint64, data []byte) error {
 	item := new(T)
 	if err := json.Unmarshal(data, item); err != nil {
 		return errs.Encoding.WithErr(err).WithCollection(c.name)
@@ -295,7 +382,7 @@ func (c Collection[T]) insertItem(tx *Snapshot, itemID uint64, data []byte) erro
 	return nil
 }
 
-func (c Collection[T]) deleteItem(tx *Snapshot, itemID uint64) error {
+func (c *Collection[T]) deleteItem(tx *Snapshot, itemID uint64) error {
 	item, ok := c.getByID(tx, itemID)
 	if !ok {
 		return errs.NotFound
@@ -312,7 +399,7 @@ func (c Collection[T]) deleteItem(tx *Snapshot, itemID uint64) error {
 
 // upsertItem inserts or updates the item with itemID and the given serialized
 // form. It's called by
-func (c Collection[T]) upsertItem(tx *Snapshot, itemID uint64, data []byte) error {
+func (c *Collection[T]) upsertItem(tx *Snapshot, itemID uint64, data []byte) error {
 	item, ok := c.getByID(tx, itemID)
 	if ok {
 		tx.delete(c.collectionID, itemID)
@@ -335,14 +422,14 @@ func (c Collection[T]) upsertItem(tx *Snapshot, itemID uint64, data []byte) erro
 	return nil
 }
 
-func (c Collection[T]) getID(t *T) uint64 {
+func (c *Collection[T]) getID(t *T) uint64 {
 	return *((*uint64)(unsafe.Pointer(t)))
 }
 
-func (c Collection[T]) setID(t *T, id uint64) {
+func (c *Collection[T]) setID(t *T, id uint64) {
 	*((*uint64)(unsafe.Pointer(t))) = id
 }
 
-func (c Collection[T]) getState(tx *Snapshot) *collectionState[T] {
+func (c *Collection[T]) getState(tx *Snapshot) *collectionState[T] {
 	return tx.collections[c.collectionID].(*collectionState[T])
 }

mdb/db-primary.go

@@ -1,67 +0,0 @@
-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
-}
-*/

mdb/db-secondary.go

@@ -1,129 +0,0 @@
-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
-}
-*/

mdb/db-testcases_test.go

@@ -54,8 +54,8 @@ var testDBTestCases = []DBTestCase{{
 		Name: "Update",
 
 		Update: func(t *testing.T, db TestDB, tx *Snapshot) error {
-			user, ok := db.Users.ByID.Get(tx, &User{ID: 1})
-			if !ok {
+			user := db.Users.ByID.Get(tx, &User{ID: 1})
+			if user == nil {
 				return errs.NotFound
 			}
 			user.Name = "Bob"
@@ -323,8 +323,8 @@ var testDBTestCases = []DBTestCase{{
 		Name: "Update",
 
 		Update: func(t *testing.T, db TestDB, tx *Snapshot) error {
-			user, ok := db.Users.ByID.Get(tx, &User{ID: 1})
-			if !ok {
+			user := db.Users.ByID.Get(tx, &User{ID: 1})
+			if user == nil {
 				return errs.NotFound
 			}
 			user.Name = "Bob"
@@ -493,8 +493,8 @@ var testDBTestCases = []DBTestCase{{
 		Name: "Update",
 
 		Update: func(t *testing.T, db TestDB, tx *Snapshot) error {
-			u, ok := db.Users.ByID.Get(tx, &User{ID: 2})
-			if !ok {
+			u := db.Users.ByID.Get(tx, &User{ID: 2})
+			if u == nil {
 				return errs.NotFound
 			}
 
@@ -609,16 +609,16 @@ var testDBTestCases = []DBTestCase{{
 		Update: func(t *testing.T, db TestDB, tx *Snapshot) error {
 			expected := &User{ID: 1, Name: "Alice", Email: "a@b.com"}
 
-			u, ok := db.Users.ByID.Get(tx, &User{ID: 1})
-			if !ok {
+			u := db.Users.ByID.Get(tx, &User{ID: 1})
+			if u == nil {
 				return errs.NotFound
 			}
 			if !reflect.DeepEqual(u, expected) {
 				return errors.New("Not equal (id)")
 			}
 
-			u, ok = db.Users.ByEmail.Get(tx, &User{Email: "a@b.com"})
-			if !ok {
+			u = db.Users.ByEmail.Get(tx, &User{Email: "a@b.com"})
+			if u == nil {
 				return errs.NotFound
 			}
 			if !reflect.DeepEqual(u, expected) {
@@ -637,11 +637,11 @@ var testDBTestCases = []DBTestCase{{
 		Name: "Get not found",
 
 		Update: func(t *testing.T, db TestDB, tx *Snapshot) error {
-			if _, ok := db.Users.ByID.Get(tx, &User{ID: 2}); ok {
+			if u := db.Users.ByID.Get(tx, &User{ID: 2}); u != nil {
 				return errors.New("Found (id)")
 			}
 
-			if _, ok := db.Users.ByEmail.Get(tx, &User{Email: "x@b.com"}); ok {
+			if u := db.Users.ByEmail.Get(tx, &User{Email: "x@b.com"}); u != nil {
 				return errors.New("Found (email)")
 			}
 
@@ -743,29 +743,25 @@ var testDBTestCases = []DBTestCase{{
 
 			first := true
 			pivot := User{Name: "User1"}
-			db.Users.ByName.AscendAfter(tx, &pivot, func(u *User) bool {
+			for u := range db.Users.ByName.AscendAfter(tx, &pivot) {
 				u.Name += "Mod"
 				if err = db.Users.Update(tx, u); err != nil {
-					return false
+					return err
 				}
 				if first {
 					first = false
-					return true
+					continue
 				}
 
-				prev, ok := db.Users.ByID.Get(tx, &User{ID: u.ID - 1})
-				if !ok {
-					err = errors.New("Previous user not found")
-					return false
+				prev := db.Users.ByID.Get(tx, &User{ID: u.ID - 1})
+				if prev == nil {
+					return errors.New("Previous user not found")
 				}
 
 				if !strings.HasSuffix(prev.Name, "Mod") {
-					err = errors.New("Incorrect user name: " + prev.Name)
-					return false
+					return errors.New("Incorrect user name: " + prev.Name)
+				}
 			}
-
-				return true
-			})
 			return nil
 		},
 
@@ -801,29 +797,26 @@ var testDBTestCases = []DBTestCase{{
 			}
 
 			first := true
-			db.Users.ByName.DescendAfter(tx, &User{Name: "User5Mod"}, func(u *User) bool {
+			for u := range db.Users.ByName.DescendAfter(tx, &User{Name: "User5Mod"}) {
 				u.Name = strings.TrimSuffix(u.Name, "Mod")
 				if err = db.Users.Update(tx, u); err != nil {
-					return false
+					return err
 				}
 				if first {
 					first = false
-					return true
+					continue
 				}
 
-				prev, ok := db.Users.ByID.Get(tx, &User{ID: u.ID + 1})
-				if !ok {
-					err = errors.New("Previous user not found")
-					return false
+				prev := db.Users.ByID.Get(tx, &User{ID: u.ID + 1})
+				if prev == nil {
+					return errors.New("Previous user not found")
 				}
 
 				if strings.HasSuffix(prev.Name, "Mod") {
-					err = errors.New("Incorrect user name: " + prev.Name)
-					return false
+					return errors.New("Incorrect user name: " + prev.Name)
+				}
 			}
 
-				return true
-			})
 			return nil
 		},
 

mdb/db-testlist_test.go

@@ -1,138 +0,0 @@
-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)
-				}
-			}
-		})
-	}
-}

mdb/db-testrunner_test.go

@@ -134,23 +134,23 @@ func checkSlicesEqual[T any](t *testing.T, name string, actual, expected []T) {
 	}
 }
 
-func checkMinMaxEqual[T any](t *testing.T, name string, tx *Snapshot, index Index[T], expected []T) {
+func checkMinMaxEqual[T any](t *testing.T, name string, tx *Snapshot, index *Index[T], expected []T) {
 	if len(expected) == 0 {
-		if min, ok := index.Min(tx); ok {
+		if min := index.Min(tx); min != nil {
 			t.Fatal(min)
 		}
-		if max, ok := index.Max(tx); ok {
+		if max := index.Max(tx); max != nil {
 			t.Fatal(max)
 		}
 		return
 	}
 
-	min, ok := index.Min(tx)
-	if !ok {
+	min := index.Min(tx)
+	if min == nil {
 		t.Fatal("No min")
 	}
-	max, ok := index.Max(tx)
-	if !ok {
+	max := index.Max(tx)
+	if max == nil {
 		t.Fatal("No max")
 	}
 

mdb/db-userdata_test.go

@@ -14,7 +14,7 @@ type UserDataItem struct {
 
 type UserData struct {
 	*Collection[UserDataItem]
-	ByName Index[UserDataItem] // Unique index on (Token).
+	ByName *Index[UserDataItem] // Unique index on (Token).
 }
 
 func NewUserDataCollection(db *Database) UserData {

mdb/db-users_test.go

@@ -12,9 +12,9 @@ type User struct {
 
 type Users struct {
 	*Collection[User]
-	ByEmail   Index[User] // Unique index on (Email).
-	ByName    Index[User] // Index on (Name).
-	ByBlocked Index[User] // Partial index on (Blocked,Email).
+	ByEmail   *Index[User] // Unique index on (Email).
+	ByName    *Index[User] // Index on (Name).
+	ByBlocked *Index[User] // Partial index on (Blocked,Email).
 }
 
 func NewUserCollection(db *Database) Users {

mdb/db.go

@@ -73,6 +73,10 @@ type Database struct {
 }
 
 func New(conf Config) *Database {
+	if conf.NetTimeout <= 0 {
+		conf.NetTimeout = time.Minute
+	}
+
 	if conf.MaxConcurrentUpdates <= 0 {
 		conf.MaxConcurrentUpdates = 32
 	}

mdb/equality_test.go

@@ -1,7 +1,6 @@
 package mdb
 
 import (
-	"fmt"
 	"reflect"
 	"testing"
 )
@@ -20,18 +19,16 @@ func (i Index[T]) AssertEqual(t *testing.T, tx1, tx2 *Snapshot) {
 	}
 
 	errStr := ""
-	i.Ascend(tx1, func(item1 *T) bool {
-		item2, ok := i.Get(tx2, item1)
-		if !ok {
-			errStr = fmt.Sprintf("Indices don't match. %v not found.", item1)
-			return false
+	iter := i.Ascend(tx1)
+	for item1 := range iter {
+		item2 := i.Get(tx2, item1)
+		if item2 == nil {
+			t.Fatalf("Indices don't match. %v not found.", item1)
 		}
 		if !reflect.DeepEqual(item1, item2) {
-			errStr = fmt.Sprintf("%v != %v", item1, item2)
-			return false
+			t.Fatalf("%v != %v", item1, item2)
+		}
 	}
-		return true
-	})
 
 	if errStr != "" {
 		t.Fatal(errStr)

mdb/index.go

@@ -1,6 +1,7 @@
 package mdb
 
 import (
+	"iter"
 	"unsafe"
 
 	"github.com/google/btree"
@@ -10,7 +11,7 @@ func NewIndex[T any](
 	c *Collection[T],
 	name string,
 	compare func(lhs, rhs *T) int,
-) Index[T] {
+) *Index[T] {
 	return c.addIndex(indexConfig[T]{
 		Name:    name,
 		Unique:  false,
@@ -24,7 +25,7 @@ func NewPartialIndex[T any](
 	name string,
 	compare func(lhs, rhs *T) int,
 	include func(*T) bool,
-) Index[T] {
+) *Index[T] {
 	return c.addIndex(indexConfig[T]{
 		Name:    name,
 		Unique:  false,
@@ -37,7 +38,7 @@ func NewUniqueIndex[T any](
 	c *Collection[T],
 	name string,
 	compare func(lhs, rhs *T) int,
-) Index[T] {
+) *Index[T] {
 	return c.addIndex(indexConfig[T]{
 		Name:    name,
 		Unique:  true,
@@ -51,7 +52,7 @@ func NewUniquePartialIndex[T any](
 	name string,
 	compare func(lhs, rhs *T) int,
 	include func(*T) bool,
-) Index[T] {
+) *Index[T] {
 	return c.addIndex(indexConfig[T]{
 		Name:    name,
 		Unique:  true,
@@ -63,6 +64,7 @@ func NewUniquePartialIndex[T any](
 // ----------------------------------------------------------------------------
 
 type Index[T any] struct {
+	db           *Database
 	name         string
 	collectionID uint64
 	indexID      uint64
@@ -70,117 +72,94 @@ type Index[T any] struct {
 	copy         func(*T) *T
 }
 
-func (i Index[T]) Get(tx *Snapshot, in *T) (item *T, ok bool) {
-	tPtr, ok := i.get(tx, in)
-	if !ok {
-		return item, false
+func (i *Index[T]) ensureSnapshot(tx *Snapshot) *Snapshot {
+	if tx == nil {
+		tx = i.db.Snapshot()
 	}
-	return i.copy(tPtr), true
+	return tx
 }
 
-func (i Index[T]) get(tx *Snapshot, in *T) (*T, bool) {
+func (i *Index[T]) Get(tx *Snapshot, in *T) *T {
+	tx = i.ensureSnapshot(tx)
+	if tPtr, ok := i.get(tx, in); ok {
+		return i.copy(tPtr)
+	}
+	return nil
+}
+
+func (i *Index[T]) get(tx *Snapshot, in *T) (*T, bool) {
 	return i.btree(tx).Get(in)
 }
 
-func (i Index[T]) Has(tx *Snapshot, in *T) bool {
+func (i *Index[T]) Has(tx *Snapshot, in *T) bool {
+	tx = i.ensureSnapshot(tx)
 	return i.btree(tx).Has(in)
 }
 
-func (i Index[T]) Min(tx *Snapshot) (item *T, ok bool) {
-	tPtr, ok := i.btree(tx).Min()
-	if !ok {
-		return item, false
+func (i *Index[T]) Min(tx *Snapshot) *T {
+	tx = i.ensureSnapshot(tx)
+	if tPtr, ok := i.btree(tx).Min(); ok {
+		return i.copy(tPtr)
 	}
-	return i.copy(tPtr), true
-}
-
-func (i Index[T]) Max(tx *Snapshot) (item *T, ok bool) {
-	tPtr, ok := i.btree(tx).Max()
-	if !ok {
-		return item, false
-	}
-	return i.copy(tPtr), true
-}
-
-func (i Index[T]) Ascend(tx *Snapshot, each func(*T) bool) {
-	i.btreeForIter(tx).Ascend(func(t *T) bool {
-		return each(i.copy(t))
-	})
-}
-
-func (i Index[T]) AscendAfter(tx *Snapshot, after *T, each func(*T) bool) {
-	i.btreeForIter(tx).AscendGreaterOrEqual(after, func(t *T) bool {
-		return each(i.copy(t))
-	})
-}
-
-func (i Index[T]) Descend(tx *Snapshot, each func(*T) bool) {
-	i.btreeForIter(tx).Descend(func(t *T) bool {
-		return each(i.copy(t))
-	})
-}
-
-func (i Index[T]) DescendAfter(tx *Snapshot, after *T, each func(*T) bool) {
-	i.btreeForIter(tx).DescendLessOrEqual(after, func(t *T) bool {
-		return each(i.copy(t))
-	})
-}
-
-type ListArgs[T any] struct {
-	Desc  bool          // True for descending order, otherwise ascending.
-	After *T            // If after is given, iterate after (and including) the value.
-	While func(*T) bool // Continue iterating until While is false.
-	Limit int           // Maximum number of items to return. 0 => All.
-}
-
-func (i Index[T]) List(tx *Snapshot, args ListArgs[T], out []*T) []*T {
-	if args.Limit < 0 {
 	return nil
-	}
+}
 
-	if args.While == nil {
-		args.While = func(*T) bool { return true }
+func (i *Index[T]) Max(tx *Snapshot) *T {
+	tx = i.ensureSnapshot(tx)
+	if tPtr, ok := i.btree(tx).Max(); ok {
+		return i.copy(tPtr)
 	}
+	return nil
+}
 
-	size := args.Limit
-	if size == 0 {
-		size = 32 // Why not?
+func (i *Index[T]) Ascend(tx *Snapshot) iter.Seq[*T] {
+	tx = i.ensureSnapshot(tx)
+	return func(yield func(*T) bool) {
+		i.btreeForIter(tx).Ascend(func(t *T) bool {
+			return yield(i.copy(t))
+		})
 	}
+}
 
-	items := out[:0]
+func (i *Index[T]) AscendAfter(tx *Snapshot, after *T) iter.Seq[*T] {
+	tx = i.ensureSnapshot(tx)
+	return func(yield func(*T) bool) {
+		i.btreeForIter(tx).AscendGreaterOrEqual(after, func(t *T) bool {
+			return yield(i.copy(t))
+		})
+	}
+}
 
-	each := func(item *T) bool {
-		if !args.While(item) {
-			return false
-		}
-		items = append(items, item)
-		return args.Limit == 0 || len(items) < args.Limit
+func (i *Index[T]) Descend(tx *Snapshot) iter.Seq[*T] {
+	tx = i.ensureSnapshot(tx)
+	return func(yield func(*T) bool) {
+		i.btreeForIter(tx).Descend(func(t *T) bool {
+			return yield(i.copy(t))
+		})
 	}
+}
 
-	if args.Desc {
-		if args.After != nil {
-			i.DescendAfter(tx, args.After, each)
-		} else {
-			i.Descend(tx, each)
-		}
-	} else {
-		if args.After != nil {
-			i.AscendAfter(tx, args.After, each)
-		} else {
-			i.Ascend(tx, each)
-		}
+func (i *Index[T]) DescendAfter(tx *Snapshot, after *T) iter.Seq[*T] {
+	tx = i.ensureSnapshot(tx)
+	return func(yield func(*T) bool) {
+		i.btreeForIter(tx).DescendLessOrEqual(after, func(t *T) bool {
+			return yield(i.copy(t))
+		})
 	}
+}
 
-	return items
+func (i *Index[T]) Count(tx *Snapshot) int {
+	tx = i.ensureSnapshot(tx)
+	return i.btree(tx).Len()
 }
 
 // ----------------------------------------------------------------------------
 
-func (i Index[T]) insertConflict(tx *Snapshot, item *T) bool {
+func (i *Index[T]) insertConflict(tx *Snapshot, item *T) bool {
 	return i.btree(tx).Has(item)
 }
 
-func (i Index[T]) updateConflict(tx *Snapshot, item *T) bool {
+func (i *Index[T]) updateConflict(tx *Snapshot, item *T) bool {
 	current, ok := i.btree(tx).Get(item)
 	return ok && i.getID(current) != i.getID(item)
 }
@@ -188,7 +167,7 @@ func (i Index[T]) updateConflict(tx *Snapshot, item *T) bool {
 // This should only be called after insertConflict. Additionally, the caller
 // should ensure that the index has been properly cloned for write before
 // writing.
-func (i Index[T]) insert(tx *Snapshot, item *T) {
+func (i *Index[T]) insert(tx *Snapshot, item *T) {
 	if i.include != nil && !i.include(item) {
 		return
 	}
@@ -196,7 +175,7 @@ func (i Index[T]) insert(tx *Snapshot, item *T) {
 	i.btree(tx).ReplaceOrInsert(item)
 }
 
-func (i Index[T]) update(tx *Snapshot, old, new *T) {
+func (i *Index[T]) update(tx *Snapshot, old, new *T) {
 	bt := i.btree(tx)
 	bt.Delete(old)
 
@@ -204,22 +183,22 @@ func (i Index[T]) update(tx *Snapshot, old, new *T) {
 	i.insert(tx, new)
 }
 
-func (i Index[T]) delete(tx *Snapshot, item *T) {
+func (i *Index[T]) delete(tx *Snapshot, item *T) {
 	i.btree(tx).Delete(item)
 }
 
 // ----------------------------------------------------------------------------
 
-func (i Index[T]) getState(tx *Snapshot) indexState[T] {
+func (i *Index[T]) getState(tx *Snapshot) indexState[T] {
 	return tx.collections[i.collectionID].(*collectionState[T]).Indices[i.indexID]
 }
 
 // Get the current btree for get/has/update/delete, etc.
-func (i Index[T]) btree(tx *Snapshot) *btree.BTreeG[*T] {
+func (i *Index[T]) btree(tx *Snapshot) *btree.BTreeG[*T] {
 	return i.getState(tx).BTree
 }
 
-func (i Index[T]) btreeForIter(tx *Snapshot) *btree.BTreeG[*T] {
+func (i *Index[T]) btreeForIter(tx *Snapshot) *btree.BTreeG[*T] {
 	cState := tx.collections[i.collectionID].(*collectionState[T])
 	bt := cState.Indices[i.indexID].BTree
 
@@ -231,6 +210,6 @@ func (i Index[T]) btreeForIter(tx *Snapshot) *btree.BTreeG[*T] {
 	return bt
 }
 
-func (i Index[T]) getID(t *T) uint64 {
+func (i *Index[T]) getID(t *T) uint64 {
 	return *((*uint64)(unsafe.Pointer(t)))
 }

mdb/index_test.go

@@ -1,9 +1,8 @@
 package mdb
 
 func (i Index[T]) Dump(tx *Snapshot) (l []T) {
-	i.Ascend(tx, func(t *T) bool {
+	for t := range i.Ascend(tx) {
 		l = append(l, *t)
-		return true
-	})
+	}
 	return l
 }

mdb/pfile/freelist.go

@@ -51,6 +51,10 @@ func (f *freeList) Push(pages ...uint64) {
 	}
 }
 
+func (f *freeList) SetNextPage(nextPage uint64) {
+	f.nextPage = nextPage
+}
+
 func (f *freeList) Pop(count int, out []uint64) []uint64 {
 	out = out[:0]
 

mdb/pfile/index.go

@@ -13,14 +13,19 @@ type Index struct {
 }
 
 func NewIndex(f *File) (*Index, error) {
+	firstPage, err := f.pageCount()
+	if err != nil {
+		return nil, err
+	}
+
 	idx := &Index{
-		fList: newFreeList(0),
+		fList: newFreeList(firstPage),
 		aList: *newAllocList(),
 		seen:  map[[2]uint64]struct{}{},
 		mask:  []bool{},
 	}
 
-	err := f.iterate(func(pageID uint64, page dataPage) error {
+	err = f.iterate(func(pageID uint64, page dataPage) error {
 		header := page.Header()
 		switch header.PageType {
 		case pageTypeHead:

mdb/pfile/pagefile.go

@@ -134,6 +134,21 @@ func (pf *File) writePage(page dataPage, id uint64) error {
 // Reading
 // ----------------------------------------------------------------------------
 
+func (pf *File) pageCount() (uint64, error) {
+	fi, err := pf.f.Stat()
+	if err != nil {
+		return 0, errs.IO.WithErr(err)
+	}
+
+	fileSize := fi.Size()
+	if fileSize%pageSize != 0 {
+		return 0, errs.Corrupt.WithMsg("File size isn't a multiple of page size.")
+	}
+
+	maxPage := uint64(fileSize / pageSize)
+	return maxPage, nil
+}
+
 func (pf *File) iterate(each func(pageID uint64, page dataPage) error) error {
 	pf.lock.RLock()
 	defer pf.lock.RUnlock()

mdb/testdb_test.go

@@ -133,8 +133,8 @@ func (db DataDB) modifyOnce() {
 func (db DataDB) ComputeCRC(tx *Snapshot) uint32 {
 	h := crc32.NewIEEE()
 	for dataID := uint64(1); dataID < 10; dataID++ {
-		d, ok := db.Datas.ByID.Get(tx, &DataItem{ID: dataID})
-		if !ok {
+		d := db.Datas.ByID.Get(tx, &DataItem{ID: dataID})
+		if d == nil {
 			continue
 		}
 		h.Write(d.Data)
@@ -143,8 +143,8 @@ func (db DataDB) ComputeCRC(tx *Snapshot) uint32 {
 }
 
 func (db DataDB) ReadCRC(tx *Snapshot) uint32 {
-	r, ok := db.CRCs.ByID.Get(tx, &CRCItem{ID: 1})
-	if !ok {
+	r := db.CRCs.ByID.Get(tx, &CRCItem{ID: 1})
+	if r == nil {
 		return 0
 	}
 	return r.CRC32

mdb/testing/crashconsistency/main.go

@@ -136,8 +136,8 @@ func (db DataDB) modifyOnce() {
 func (db DataDB) ComputeCRC(tx *mdb.Snapshot) uint32 {
 	h := crc32.NewIEEE()
 	for dataID := uint64(1); dataID < 10; dataID++ {
-		d, ok := db.Datas.ByID.Get(tx, &DataItem{ID: dataID})
-		if !ok {
+		d := db.Datas.ByID.Get(tx, &DataItem{ID: dataID})
+		if d == nil {
 			continue
 		}
 		h.Write(d.Data)
@@ -146,8 +146,8 @@ func (db DataDB) ComputeCRC(tx *mdb.Snapshot) uint32 {
 }
 
 func (db DataDB) ReadCRC(tx *mdb.Snapshot) uint32 {
-	r, ok := db.CRCs.ByID.Get(tx, &CRCItem{ID: 1})
-	if !ok {
+	r := db.CRCs.ByID.Get(tx, &CRCItem{ID: 1})
+	if r == nil {
 		return 0
 	}
 	return r.CRC32