[#314] writecache: remove objects right after they are flushed

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/local_object_storage/writecache/flush.go

@@ -78,7 +78,7 @@ func (c *cache) flushSmallObjects() {
 		m = m[:0]
 
 		c.modeMtx.RLock()
-		if c.readOnly() || !c.initialized.Load() {
+		if c.readOnly() {
 			c.modeMtx.RUnlock()
 			time.Sleep(time.Second)
 			continue
@@ -117,10 +117,6 @@ func (c *cache) flushSmallObjects() {
 
 		var count int
 		for i := range m {
-			if c.flushed.Contains(m[i].addr) {
-				continue
-			}
-
 			obj := object.New()
 			if err := obj.Unmarshal(m[i].data); err != nil {
 				continue
@@ -157,9 +153,6 @@ func (c *cache) workerFlushBig(ctx context.Context) {
 			if c.readOnly() {
 				c.modeMtx.RUnlock()
 				break
-			} else if !c.initialized.Load() {
-				c.modeMtx.RUnlock()
-				continue
 			}
 
 			_ = c.flushFSTree(ctx, true)
@@ -187,10 +180,6 @@ func (c *cache) flushFSTree(ctx context.Context, ignoreErrors bool) error {
 	prm.LazyHandler = func(addr oid.Address, f func() ([]byte, error)) error {
 		sAddr := addr.EncodeToString()
 
-		if _, ok := c.store.flushed.Peek(sAddr); ok {
-			return nil
-		}
-
 		data, err := f()
 		if err != nil {
 			c.reportFlushError("can't read a file", sAddr, err)
@@ -218,9 +207,7 @@ func (c *cache) flushFSTree(ctx context.Context, ignoreErrors bool) error {
 			return err
 		}
 
-		// mark object as flushed
-		c.flushed.Add(sAddr, false)
-
+		c.deleteFromDisk(ctx, []string{sAddr})
 		return nil
 	}
 
@@ -242,9 +229,12 @@ func (c *cache) workerFlushSmall() {
 		}
 
 		err := c.flushObject(context.TODO(), obj, nil)
-		if err == nil {
-			c.flushed.Add(objectCore.AddressOf(obj).EncodeToString(), true)
+		if err != nil {
+			// Error is handled in flushObject.
+			continue
 		}
+
+		c.deleteFromDB([]string{objectCore.AddressOf(obj).EncodeToString()})
 	}
 }
 
@@ -306,10 +296,6 @@ func (c *cache) flush(ctx context.Context, ignoreErrors bool) error {
 		cs := b.Cursor()
 		for k, data := cs.Seek(nil); k != nil; k, data = cs.Next() {
 			sa := string(k)
-			if _, ok := c.flushed.Peek(sa); ok {
-				continue
-			}
-
 			if err := addr.DecodeString(sa); err != nil {
 				c.reportFlushError("can't decode object address from the DB", sa, err)
 				if ignoreErrors {

pkg/local_object_storage/writecache/flush_test.go

@@ -5,7 +5,6 @@ import (
 	"os"
 	"path/filepath"
 	"testing"
-	"time"
 
 	objectCore "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/core/object"
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/blobstor"
@@ -15,7 +14,6 @@ import (
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/shard/mode"
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util/logger"
 	checksumtest "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/checksum/test"
-	apistatus "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client/status"
 	cidtest "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id/test"
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
 	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
@@ -109,22 +107,9 @@ func TestFlush(t *testing.T) {
 		require.NoError(t, bs.SetMode(mode.ReadWrite))
 		require.NoError(t, mb.SetMode(mode.ReadWrite))
 
-		wc.(*cache).flushed.Add(objects[0].addr.EncodeToString(), true)
-		wc.(*cache).flushed.Add(objects[1].addr.EncodeToString(), false)
-
 		require.NoError(t, wc.Flush(context.Background(), false))
 
-		for i := 0; i < 2; i++ {
-			var mPrm meta.GetPrm
-			mPrm.SetAddress(objects[i].addr)
-			_, err := mb.Get(context.Background(), mPrm)
-			require.Error(t, err)
-
-			_, err = bs.Get(context.Background(), common.GetPrm{Address: objects[i].addr})
-			require.Error(t, err)
-		}
-
-		check(t, mb, bs, objects[2:])
+		check(t, mb, bs, objects)
 	})
 
 	t.Run("flush on moving to degraded mode", func(t *testing.T) {
@@ -138,23 +123,9 @@ func TestFlush(t *testing.T) {
 		require.NoError(t, wc.SetMode(mode.ReadOnly))
 		require.NoError(t, bs.SetMode(mode.ReadWrite))
 		require.NoError(t, mb.SetMode(mode.ReadWrite))
-
-		wc.(*cache).flushed.Add(objects[0].addr.EncodeToString(), true)
-		wc.(*cache).flushed.Add(objects[1].addr.EncodeToString(), false)
-
 		require.NoError(t, wc.SetMode(mode.Degraded))
 
-		for i := 0; i < 2; i++ {
-			var mPrm meta.GetPrm
-			mPrm.SetAddress(objects[i].addr)
-			_, err := mb.Get(context.Background(), mPrm)
-			require.Error(t, err)
-
-			_, err = bs.Get(context.Background(), common.GetPrm{Address: objects[i].addr})
-			require.Error(t, err)
-		}
-
-		check(t, mb, bs, objects[2:])
+		check(t, mb, bs, objects)
 	})
 
 	t.Run("ignore errors", func(t *testing.T) {
@@ -223,67 +194,6 @@ func TestFlush(t *testing.T) {
 			})
 		})
 	})
-
-	t.Run("on init", func(t *testing.T) {
-		wc, bs, mb := newCache(t)
-		objects := []objectPair{
-			// removed
-			putObject(t, wc, 1),
-			putObject(t, wc, smallSize+1),
-			// not found
-			putObject(t, wc, 1),
-			putObject(t, wc, smallSize+1),
-			// ok
-			putObject(t, wc, 1),
-			putObject(t, wc, smallSize+1),
-		}
-
-		require.NoError(t, wc.Close())
-		require.NoError(t, bs.SetMode(mode.ReadWrite))
-		require.NoError(t, mb.SetMode(mode.ReadWrite))
-
-		for i := range objects {
-			var prm meta.PutPrm
-			prm.SetObject(objects[i].obj)
-			_, err := mb.Put(context.Background(), prm)
-			require.NoError(t, err)
-		}
-
-		var inhumePrm meta.InhumePrm
-		inhumePrm.SetAddresses(objects[0].addr, objects[1].addr)
-		inhumePrm.SetTombstoneAddress(oidtest.Address())
-		_, err := mb.Inhume(context.Background(), inhumePrm)
-		require.NoError(t, err)
-
-		var deletePrm meta.DeletePrm
-		deletePrm.SetAddresses(objects[2].addr, objects[3].addr)
-		_, err = mb.Delete(context.Background(), deletePrm)
-		require.NoError(t, err)
-
-		require.NoError(t, bs.SetMode(mode.ReadOnly))
-		require.NoError(t, mb.SetMode(mode.ReadOnly))
-
-		// Open in read-only: no error, nothing is removed.
-		require.NoError(t, wc.Open(true))
-		initWC(t, wc)
-		for i := range objects {
-			_, err := wc.Get(context.Background(), objects[i].addr)
-			require.NoError(t, err, i)
-		}
-		require.NoError(t, wc.Close())
-
-		// Open in read-write: no error, something is removed.
-		require.NoError(t, wc.Open(false))
-		initWC(t, wc)
-		for i := range objects {
-			_, err := wc.Get(context.Background(), objects[i].addr)
-			if i < 2 {
-				require.ErrorAs(t, err, new(apistatus.ObjectNotFound), i)
-			} else {
-				require.NoError(t, err, i)
-			}
-		}
-	})
 }
 
 func putObject(t *testing.T, c Cache, size int) objectPair {
@@ -321,11 +231,6 @@ func newObject(t *testing.T, size int) (*object.Object, []byte) {
 
 func initWC(t *testing.T, wc Cache) {
 	require.NoError(t, wc.Init())
-
-	require.Eventually(t, func() bool {
-		rawWc := wc.(*cache)
-		return rawWc.initialized.Load()
-	}, 100*time.Second, 1*time.Millisecond)
 }
 
 type dummyEpoch struct{}

pkg/local_object_storage/writecache/get.go

@@ -30,7 +30,6 @@ func (c *cache) Get(ctx context.Context, addr oid.Address) (*objectSDK.Object, e
 	value, err := Get(c.db, []byte(saddr))
 	if err == nil {
 		obj := objectSDK.New()
-		c.flushed.Get(saddr)
 		return obj, obj.Unmarshal(value)
 	}
 
@@ -39,7 +38,6 @@ func (c *cache) Get(ctx context.Context, addr oid.Address) (*objectSDK.Object, e
 		return nil, logicerr.Wrap(apistatus.ObjectNotFound{})
 	}
 
-	c.flushed.Get(saddr)
 	return res.Object, nil
 }
 

pkg/local_object_storage/writecache/init.go

@@ -1,192 +0,0 @@
-package writecache
-
-import (
-	"context"
-	"errors"
-	"sync"
-
-	"git.frostfs.info/TrueCloudLab/frostfs-node/internal/logs"
-	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/blobstor/common"
-	storagelog "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/internal/log"
-	meta "git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/metabase"
-	apistatus "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client/status"
-	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
-	"go.etcd.io/bbolt"
-	"go.uber.org/zap"
-)
-
-func (c *cache) initFlushMarks(ctx context.Context) {
-	var localWG sync.WaitGroup
-
-	localWG.Add(1)
-	go func() {
-		defer localWG.Done()
-
-		c.fsTreeFlushMarkUpdate(ctx)
-	}()
-
-	localWG.Add(1)
-	go func() {
-		defer localWG.Done()
-
-		c.dbFlushMarkUpdate(ctx)
-	}()
-
-	c.initWG.Add(1)
-	c.wg.Add(1)
-	go func() {
-		defer c.wg.Done()
-		defer c.initWG.Done()
-
-		localWG.Wait()
-
-		select {
-		case <-c.stopInitCh:
-			return
-		case <-c.closeCh:
-			return
-		default:
-		}
-
-		c.initialized.Store(true)
-	}()
-}
-
-var errStopIter = errors.New("stop iteration")
-
-func (c *cache) fsTreeFlushMarkUpdate(ctx context.Context) {
-	c.log.Info(logs.WritecacheFillingFlushMarksForObjectsInFSTree)
-
-	var prm common.IteratePrm
-	prm.LazyHandler = func(addr oid.Address, _ func() ([]byte, error)) error {
-		select {
-		case <-c.closeCh:
-			return errStopIter
-		case <-c.stopInitCh:
-			return errStopIter
-		default:
-		}
-
-		flushed, needRemove := c.flushStatus(ctx, addr)
-		if flushed {
-			c.store.flushed.Add(addr.EncodeToString(), true)
-			if needRemove {
-				var prm common.DeletePrm
-				prm.Address = addr
-
-				_, err := c.fsTree.Delete(ctx, prm)
-				if err == nil {
-					storagelog.Write(c.log,
-						storagelog.AddressField(addr),
-						storagelog.StorageTypeField(wcStorageType),
-						storagelog.OpField("fstree DELETE"),
-					)
-				}
-			}
-		}
-		return nil
-	}
-
-	c.modeMtx.RLock()
-	defer c.modeMtx.RUnlock()
-
-	_, _ = c.fsTree.Iterate(prm)
-
-	c.log.Info(logs.WritecacheFinishedUpdatingFSTreeFlushMarks)
-}
-
-func (c *cache) dbFlushMarkUpdate(ctx context.Context) {
-	c.log.Info(logs.WritecacheFillingFlushMarksForObjectsInDatabase)
-
-	c.modeMtx.RLock()
-	defer c.modeMtx.RUnlock()
-
-	var m []string
-	var indices []int
-	var lastKey []byte
-	var batchSize = flushBatchSize
-	for {
-		select {
-		case <-c.closeCh:
-			return
-		case <-c.stopInitCh:
-			return
-		default:
-		}
-
-		m = m[:0]
-		indices = indices[:0]
-
-		// We put objects in batches of fixed size to not interfere with main put cycle a lot.
-		_ = c.db.View(func(tx *bbolt.Tx) error {
-			b := tx.Bucket(defaultBucket)
-			cs := b.Cursor()
-			for k, _ := cs.Seek(lastKey); k != nil && len(m) < batchSize; k, _ = cs.Next() {
-				m = append(m, string(k))
-			}
-			return nil
-		})
-
-		var addr oid.Address
-		for i := range m {
-			if err := addr.DecodeString(m[i]); err != nil {
-				continue
-			}
-
-			flushed, needRemove := c.flushStatus(ctx, addr)
-			if flushed {
-				c.store.flushed.Add(addr.EncodeToString(), true)
-				if needRemove {
-					indices = append(indices, i)
-				}
-			}
-		}
-
-		if len(m) == 0 {
-			break
-		}
-
-		err := c.db.Batch(func(tx *bbolt.Tx) error {
-			b := tx.Bucket(defaultBucket)
-			for _, j := range indices {
-				if err := b.Delete([]byte(m[j])); err != nil {
-					return err
-				}
-			}
-			return nil
-		})
-		if err == nil {
-			for _, j := range indices {
-				storagelog.Write(c.log,
-					zap.String("address", m[j]),
-					storagelog.StorageTypeField(wcStorageType),
-					storagelog.OpField("db DELETE"),
-				)
-			}
-		}
-		lastKey = append([]byte(m[len(m)-1]), 0)
-	}
-
-	c.log.Info(logs.WritecacheFinishedUpdatingFlushMarks)
-}
-
-// flushStatus returns info about the object state in the main storage.
-// First return value is true iff object exists.
-// Second return value is true iff object can be safely removed.
-func (c *cache) flushStatus(ctx context.Context, addr oid.Address) (bool, bool) {
-	var existsPrm meta.ExistsPrm
-	existsPrm.SetAddress(addr)
-
-	_, err := c.metabase.Exists(ctx, existsPrm)
-	if err != nil {
-		needRemove := errors.Is(err, meta.ErrObjectIsExpired) || errors.As(err, new(apistatus.ObjectAlreadyRemoved))
-		return needRemove, needRemove
-	}
-
-	var prm meta.StorageIDPrm
-	prm.SetAddress(addr)
-
-	mRes, _ := c.metabase.StorageID(ctx, prm)
-	res, err := c.blobstor.Exists(ctx, common.ExistsPrm{Address: addr, StorageID: mRes.StorageID()})
-	return err == nil && res.Exists, false
-}

pkg/local_object_storage/writecache/iterate.go

@@ -41,9 +41,6 @@ func (c *cache) Iterate(prm IterationPrm) error {
 	err := c.db.View(func(tx *bbolt.Tx) error {
 		b := tx.Bucket(defaultBucket)
 		return b.ForEach(func(k, data []byte) error {
-			if _, ok := c.flushed.Peek(string(k)); ok {
-				return nil
-			}
 			return prm.handler(data)
 		})
 	})
@@ -54,9 +51,6 @@ func (c *cache) Iterate(prm IterationPrm) error {
 	var fsPrm common.IteratePrm
 	fsPrm.IgnoreErrors = prm.ignoreErrors
 	fsPrm.LazyHandler = func(addr oid.Address, f func() ([]byte, error)) error {
-		if _, ok := c.flushed.Peek(addr.EncodeToString()); ok {
-			return nil
-		}
 		data, err := f()
 		if err != nil {
 			if prm.ignoreErrors {

pkg/local_object_storage/writecache/mode.go

@@ -37,22 +37,6 @@ func (c *cache) setMode(ctx context.Context, m mode.Mode) error {
 	var err error
 	turnOffMeta := m.NoMetabase()
 
-	if !c.initialized.Load() {
-		close(c.stopInitCh)
-
-		c.initWG.Wait()
-		c.stopInitCh = make(chan struct{})
-
-		defer func() {
-			if err == nil && !turnOffMeta {
-				c.initFlushMarks(ctx)
-			}
-		}()
-	}
-
-	c.modeMtx.Lock()
-	defer c.modeMtx.Unlock()
-
 	if turnOffMeta && !c.mode.NoMetabase() {
 		err = c.flush(ctx, true)
 		if err != nil {

pkg/local_object_storage/writecache/put.go

@@ -37,8 +37,6 @@ func (c *cache) Put(ctx context.Context, prm common.PutPrm) (common.PutRes, erro
 	defer c.modeMtx.RUnlock()
 	if c.readOnly() {
 		return common.PutRes{}, ErrReadOnly
-	} else if !c.initialized.Load() {
-		return common.PutRes{}, ErrNotInitialized
 	}
 
 	sz := uint64(len(prm.RawData))

pkg/local_object_storage/writecache/storage.go

@@ -13,8 +13,6 @@ import (
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util"
 	apistatus "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/client/status"
 	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
-	lru "github.com/hashicorp/golang-lru/v2"
-	"github.com/hashicorp/golang-lru/v2/simplelru"
 	"go.etcd.io/bbolt"
 	"go.uber.org/zap"
 )
@@ -22,19 +20,7 @@ import (
 // store represents persistent storage with in-memory LRU cache
 // for flushed items on top of it.
 type store struct {
-	maxFlushedMarksCount int
-	maxRemoveBatchSize   int
-
-	// flushed contains addresses of objects that were already flushed to the main storage.
-	// We use LRU cache instead of map here to facilitate removing of unused object in favour of
-	// frequently read ones.
-	// MUST NOT be used inside bolt db transaction because it's eviction handler
-	// removes untracked items from the database.
-	flushed simplelru.LRUCache[string, bool]
 	db *bbolt.DB
-
-	dbKeysToRemove []string
-	fsKeysToRemove []string
 }
 
 const dbName = "small.bolt"
@@ -73,35 +59,9 @@ func (c *cache) openStore(readOnly bool) error {
 		return fmt.Errorf("could not open FSTree: %w", err)
 	}
 
-	// Write-cache can be opened multiple times during `SetMode`.
-	// flushed map must not be re-created in this case.
-	if c.flushed == nil {
-		c.flushed, _ = lru.NewWithEvict[string, bool](c.maxFlushedMarksCount, c.removeFlushed)
-	}
-
-	c.initialized.Store(false)
-
 	return nil
 }
 
-// removeFlushed removes an object from the writecache.
-// To minimize interference with the client operations, the actual removal
-// is done in batches.
-// It is not thread-safe and is used only as an evict callback to LRU cache.
-func (c *cache) removeFlushed(key string, value bool) {
-	fromDatabase := value
-	if fromDatabase {
-		c.dbKeysToRemove = append(c.dbKeysToRemove, key)
-	} else {
-		c.fsKeysToRemove = append(c.fsKeysToRemove, key)
-	}
-
-	if len(c.dbKeysToRemove)+len(c.fsKeysToRemove) >= c.maxRemoveBatchSize {
-		c.dbKeysToRemove = c.deleteFromDB(c.dbKeysToRemove)
-		c.fsKeysToRemove = c.deleteFromDisk(c.fsKeysToRemove)
-	}
-}
-
 func (c *cache) deleteFromDB(keys []string) []string {
 	if len(keys) == 0 {
 		return keys
@@ -133,7 +93,7 @@ func (c *cache) deleteFromDB(keys []string) []string {
 	return keys[:len(keys)-errorIndex]
 }
 
-func (c *cache) deleteFromDisk(keys []string) []string {
+func (c *cache) deleteFromDisk(ctx context.Context, keys []string) []string {
 	if len(keys) == 0 {
 		return keys
 	}
@@ -147,7 +107,7 @@ func (c *cache) deleteFromDisk(keys []string) []string {
 			continue
 		}
 
-		_, err := c.fsTree.Delete(context.TODO(), common.DeletePrm{Address: addr})
+		_, err := c.fsTree.Delete(ctx, common.DeletePrm{Address: addr})
 		if err != nil && !errors.As(err, new(apistatus.ObjectNotFound)) {
 			c.log.Error(logs.WritecacheCantRemoveObjectFromWritecache, zap.Error(err))
 

pkg/local_object_storage/writecache/writecache.go

@@ -5,7 +5,6 @@ import (
 	"os"
 	"sync"
 
-	"git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/pkg/tracing"
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/blobstor/common"
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/blobstor/fstree"
 	"git.frostfs.info/TrueCloudLab/frostfs-node/pkg/local_object_storage/shard/mode"
@@ -13,7 +12,6 @@ import (
 	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
 	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
 	"go.etcd.io/bbolt"
-	"go.uber.org/atomic"
 	"go.uber.org/zap"
 )
 
@@ -53,9 +51,6 @@ type cache struct {
 	mtx sync.RWMutex
 
 	mode    mode.Mode
-	initialized atomic.Bool
-	stopInitCh  chan struct{}  // used to sync initWG initialisation routines and _only_ them
-	initWG      sync.WaitGroup // for initialisation routines only
 	modeMtx sync.RWMutex
 
 	// compressFlags maps address of a big object to boolean value indicating
@@ -98,7 +93,6 @@ func New(opts ...Option) Cache {
 	c := &cache{
 		flushCh: make(chan *object.Object),
 		mode:    mode.ReadWrite,
-		stopInitCh: make(chan struct{}),
 
 		compressFlags: make(map[string]struct{}),
 		options: options{
@@ -117,12 +111,6 @@ func New(opts ...Option) Cache {
 		opts[i](&c.options)
 	}
 
-	// Make the LRU cache contain which take approximately 3/4 of the maximum space.
-	// Assume small and big objects are stored in 50-50 proportion.
-	c.maxFlushedMarksCount = int(c.maxCacheSize/c.maxObjectSize+c.maxCacheSize/c.smallObjectSize) / 2 * 3 / 4
-	// Trigger the removal when the cache is 7/8 full, so that new items can still arrive.
-	c.maxRemoveBatchSize = c.maxFlushedMarksCount / 8
-
 	return c
 }
 
@@ -153,31 +141,27 @@ func (c *cache) Open(readOnly bool) error {
 
 // Init runs necessary services.
 func (c *cache) Init() error {
-	ctx, span := tracing.StartSpanFromContext(context.TODO(), "writecache.Init")
-	defer span.End()
-
-	c.initFlushMarks(ctx)
 	c.runFlushLoop()
 	return nil
 }
 
 // Close closes db connection and stops services. Executes ObjectCounters.FlushAndClose op.
 func (c *cache) Close() error {
-	// Finish all in-progress operations.
-	if err := c.setMode(context.TODO(), mode.ReadOnly); err != nil {
-		return err
-	}
-
+	// We cannot lock mutex for the whole operation duration
+	// because it is taken by some background workers, so `wg.Wait()` is done without modeMtx.
+	c.modeMtx.Lock()
 	if c.closeCh != nil {
 		close(c.closeCh)
 	}
+	c.mode = mode.DegradedReadOnly // prevent new operations from being processed
+	c.modeMtx.Unlock()
+
 	c.wg.Wait()
-	if c.closeCh != nil {
+
+	c.modeMtx.Lock()
+	defer c.modeMtx.Unlock()
+
 	c.closeCh = nil
-	}
-
-	c.initialized.Store(false)
-
 	var err error
 	if c.db != nil {
 		err = c.db.Close()