Refactor database code to support standalone batches, transactions.

This is spin-off of changes from #459.

Transactions are not being used yet, but batches are updated to work
with the new API.

`database/` package was refactored to split abstract interfaces and
implementation via goleveldb. This should make it easier to implement
new database types.

cmd/db_cleanup.go

@@ -183,15 +183,15 @@ func aptlyDbCleanup(cmd *commander.Command, args []string) error {
 		}
 
 		if !dryRun {
-			db.StartBatch()
+			batch := db.CreateBatch()
 			err = toDelete.ForEach(func(ref []byte) error {
-				return context.CollectionFactory().PackageCollection().DeleteByKey(ref)
+				return context.CollectionFactory().PackageCollection().DeleteByKey(ref, batch)
 			})
 			if err != nil {
 				return err
 			}
 
-			err = db.FinishBatch()
+			err = batch.Write()
 			if err != nil {
 				return fmt.Errorf("unable to write to DB: %s", err)
 			}

cmd/db_recover.go

@@ -1,8 +1,9 @@
 package cmd
 
 import (
-	"github.com/aptly-dev/aptly/database"
 	"github.com/smira/commander"
+
+	"github.com/aptly-dev/aptly/database/goleveldb"
 )
 
 // aptly db recover
@@ -15,7 +16,7 @@ func aptlyDbRecover(cmd *commander.Command, args []string) error {
 	}
 
 	context.Progress().Printf("Recovering database...\n")
-	err = database.RecoverDB(context.DBPath())
+	err = goleveldb.RecoverDB(context.DBPath())
 
 	return err
 }

context/context.go

@@ -17,6 +17,7 @@ import (
 	"github.com/aptly-dev/aptly/aptly"
 	"github.com/aptly-dev/aptly/console"
 	"github.com/aptly-dev/aptly/database"
+	"github.com/aptly-dev/aptly/database/goleveldb"
 	"github.com/aptly-dev/aptly/deb"
 	"github.com/aptly-dev/aptly/files"
 	"github.com/aptly-dev/aptly/http"
@@ -244,7 +245,7 @@ func (context *AptlyContext) _database() (database.Storage, error) {
 	if context.database == nil {
 		var err error
 
-		context.database, err = database.NewDB(context.dbPath())
+		context.database, err = goleveldb.NewDB(context.dbPath())
 		if err != nil {
 			return nil, fmt.Errorf("can't instantiate database: %s", err)
 		}

database/database.go

@@ -0,0 +1,69 @@
+// Package database provides KV database for meta-information
+package database
+
+import "errors"
+
+// Errors for Storage
+var (
+	ErrNotFound = errors.New("key not found")
+)
+
+// StorageProcessor is a function to process one single storage entry
+type StorageProcessor func(key []byte, value []byte) error
+
+// Reader provides KV read calls
+type Reader interface {
+	Get(key []byte) ([]byte, error)
+}
+
+// PrefixReader provides prefixed operations
+type PrefixReader interface {
+	HasPrefix(prefix []byte) bool
+	ProcessByPrefix(prefix []byte, proc StorageProcessor) error
+	KeysByPrefix(prefix []byte) [][]byte
+	FetchByPrefix(prefix []byte) [][]byte
+}
+
+// Writer provides KV update/delete calls
+type Writer interface {
+	Put(key []byte, value []byte) error
+	Delete(key []byte) error
+}
+
+// Storage is an interface to KV storage
+type Storage interface {
+	Reader
+	Writer
+
+	PrefixReader
+
+	CreateBatch() Batch
+	OpenTransaction() (Transaction, error)
+
+	CreateTemporary() (Storage, error)
+
+	Open() error
+	Close() error
+	CompactDB() error
+	Drop() error
+}
+
+// Batch provides a way to pack many writes.
+type Batch interface {
+	Writer
+
+	// Write closes batch and send accumulated writes to the database
+	Write() error
+}
+
+// Transaction provides isolated atomic way to perform updates.
+//
+// Transactions might be expensive.
+// Transaction should always finish with either Discard() or Commit()
+type Transaction interface {
+	Reader
+	Writer
+
+	Commit() error
+	Discard()
+}

database/goleveldb/batch.go

@@ -0,0 +1,34 @@
+package goleveldb
+
+import (
+	"github.com/syndtr/goleveldb/leveldb"
+	"github.com/syndtr/goleveldb/leveldb/opt"
+
+	"github.com/aptly-dev/aptly/database"
+)
+
+type batch struct {
+	db *leveldb.DB
+	b  *leveldb.Batch
+}
+
+func (b *batch) Put(key, value []byte) error {
+	b.b.Put(key, value)
+
+	return nil
+}
+
+func (b *batch) Delete(key []byte) error {
+	b.b.Delete(key)
+
+	return nil
+}
+
+func (b *batch) Write() error {
+	return b.db.Write(b.b, &opt.WriteOptions{})
+}
+
+// batch should implement database.Batch
+var (
+	_ database.Batch = &batch{}
+)

database/goleveldb/database.go

@@ -0,0 +1,58 @@
+package goleveldb
+
+import (
+	"github.com/syndtr/goleveldb/leveldb"
+	"github.com/syndtr/goleveldb/leveldb/filter"
+	"github.com/syndtr/goleveldb/leveldb/opt"
+	leveldbstorage "github.com/syndtr/goleveldb/leveldb/storage"
+
+	"github.com/aptly-dev/aptly/database"
+)
+
+func internalOpen(path string, throttleCompaction bool) (*leveldb.DB, error) {
+	o := &opt.Options{
+		Filter:                 filter.NewBloomFilter(10),
+		OpenFilesCacheCapacity: 256,
+	}
+
+	if throttleCompaction {
+		o.CompactionL0Trigger = 32
+		o.WriteL0PauseTrigger = 96
+		o.WriteL0SlowdownTrigger = 64
+	}
+
+	return leveldb.OpenFile(path, o)
+}
+
+// NewDB creates new instance of DB, but doesn't open it (yet)
+func NewDB(path string) (database.Storage, error) {
+	return &storage{path: path}, nil
+}
+
+// NewOpenDB creates new instance of DB and opens it
+func NewOpenDB(path string) (database.Storage, error) {
+	db, err := NewDB(path)
+	if err != nil {
+		return nil, err
+	}
+
+	return db, db.Open()
+}
+
+// RecoverDB recovers LevelDB database from corruption
+func RecoverDB(path string) error {
+	stor, err := leveldbstorage.OpenFile(path, false)
+	if err != nil {
+		return err
+	}
+
+	db, err := leveldb.Recover(stor, nil)
+	if err != nil {
+		return err
+	}
+
+	db.Close()
+	stor.Close()
+
+	return nil
+}

database/leveldb_test.go → database/goleveldb/database_test.go

@@ -1,9 +1,12 @@
-package database
+package goleveldb_test
 
 import (
 	"testing"
 
 	. "gopkg.in/check.v1"
+
+	"github.com/aptly-dev/aptly/database"
+	"github.com/aptly-dev/aptly/database/goleveldb"
 )
 
 // Launch gocheck tests
@@ -13,7 +16,7 @@ func Test(t *testing.T) {
 
 type LevelDBSuite struct {
 	path string
-	db   Storage
+	db   database.Storage
 }
 
 var _ = Suite(&LevelDBSuite{})
@@ -22,7 +25,7 @@ func (s *LevelDBSuite) SetUpTest(c *C) {
 	var err error
 
 	s.path = c.MkDir()
-	s.db, err = NewOpenDB(s.path)
+	s.db, err = goleveldb.NewOpenDB(s.path)
 	c.Assert(err, IsNil)
 }
 
@@ -43,10 +46,10 @@ func (s *LevelDBSuite) TestRecoverDB(c *C) {
 	err = s.db.Close()
 	c.Check(err, IsNil)
 
-	err = RecoverDB(s.path)
+	err = goleveldb.RecoverDB(s.path)
 	c.Check(err, IsNil)
 
-	s.db, err = NewOpenDB(s.path)
+	s.db, err = goleveldb.NewOpenDB(s.path)
 	c.Check(err, IsNil)
 
 	result, err := s.db.Get(key)
@@ -143,11 +146,11 @@ func (s *LevelDBSuite) TestByPrefix(c *C) {
 	c.Check(keys, DeepEquals, [][]byte{{0x80, 0x01}, {0x80, 0x02}, {0x80, 0x03}})
 
 	c.Check(s.db.ProcessByPrefix([]byte{0x80}, func(k, v []byte) error {
-		return ErrNotFound
-	}), Equals, ErrNotFound)
+		return database.ErrNotFound
+	}), Equals, database.ErrNotFound)
 
 	c.Check(s.db.ProcessByPrefix([]byte{0xa0}, func(k, v []byte) error {
-		return ErrNotFound
+		return database.ErrNotFound
 	}), IsNil)
 
 	c.Check(s.db.FetchByPrefix([]byte{0xa0}), DeepEquals, [][]byte{})
@@ -176,9 +179,9 @@ func (s *LevelDBSuite) TestBatch(c *C) {
 	err := s.db.Put(key, value)
 	c.Assert(err, IsNil)
 
-	s.db.StartBatch()
-	s.db.Put(key2, value2)
-	s.db.Delete(key)
+	batch := s.db.CreateBatch()
+	batch.Put(key2, value2)
+	batch.Delete(key)
 
 	v, err := s.db.Get(key)
 	c.Check(err, IsNil)
@@ -187,7 +190,7 @@ func (s *LevelDBSuite) TestBatch(c *C) {
 	_, err = s.db.Get(key2)
 	c.Check(err, ErrorMatches, "key not found")
 
-	err = s.db.FinishBatch()
+	err = batch.Write()
 	c.Check(err, IsNil)
 
 	v2, err := s.db.Get(key2)
@@ -196,11 +199,87 @@ func (s *LevelDBSuite) TestBatch(c *C) {
 
 	_, err = s.db.Get(key)
 	c.Check(err, ErrorMatches, "key not found")
+}
+
+func (s *LevelDBSuite) TestTransactionCommit(c *C) {
+	var (
+		key    = []byte("key")
+		key2   = []byte("key2")
+		value  = []byte("value")
+		value2 = []byte("value2")
+	)
+
+	err := s.db.Put(key, value)
+	c.Assert(err, IsNil)
+
+	transaction, err := s.db.OpenTransaction()
+	c.Assert(err, IsNil)
+	transaction.Put(key2, value2)
+	transaction.Delete(key)
+
+	v, err := s.db.Get(key)
+	c.Check(err, IsNil)
+	c.Check(v, DeepEquals, value)
+
+	_, err = s.db.Get(key2)
+	c.Check(err, ErrorMatches, "key not found")
+
+	v2, err := transaction.Get(key2)
+	c.Check(err, IsNil)
+	c.Check(v2, DeepEquals, value2)
+
+	_, err = transaction.Get(key)
+	c.Check(err, ErrorMatches, "key not found")
+
+	err = transaction.Commit()
+	c.Check(err, IsNil)
+
+	v2, err = s.db.Get(key2)
+	c.Check(err, IsNil)
+	c.Check(v2, DeepEquals, value2)
+
+	_, err = s.db.Get(key)
+	c.Check(err, ErrorMatches, "key not found")
+}
+
+func (s *LevelDBSuite) TestTransactionDiscard(c *C) {
+	var (
+		key    = []byte("key")
+		key2   = []byte("key2")
+		value  = []byte("value")
+		value2 = []byte("value2")
+	)
+
+	err := s.db.Put(key, value)
+	c.Assert(err, IsNil)
+
+	transaction, err := s.db.OpenTransaction()
+	c.Assert(err, IsNil)
+	transaction.Put(key2, value2)
+	transaction.Delete(key)
+
+	v, err := s.db.Get(key)
+	c.Check(err, IsNil)
+	c.Check(v, DeepEquals, value)
+
+	_, err = s.db.Get(key2)
+	c.Check(err, ErrorMatches, "key not found")
+
+	v2, err := transaction.Get(key2)
+	c.Check(err, IsNil)
+	c.Check(v2, DeepEquals, value2)
+
+	_, err = transaction.Get(key)
+	c.Check(err, ErrorMatches, "key not found")
+
+	transaction.Discard()
 
-	c.Check(func() { s.db.FinishBatch() }, Panics, "no batch")
+	v, err = s.db.Get(key)
+	c.Check(err, IsNil)
+	c.Check(v, DeepEquals, value)
 
-	s.db.StartBatch()
-	c.Check(func() { s.db.StartBatch() }, Panics, "batch already started")
+	_, err = s.db.Get(key2)
+	c.Check(err, ErrorMatches, "key not found")
 }
 
 func (s *LevelDBSuite) TestCompactDB(c *C) {

database/goleveldb/leveldb.go

@@ -0,0 +1,2 @@
+// Package goleveldb implements database interface via goleveldb
+package goleveldb