Refactor replica system

2021-05-20 18:37:54 -06:00
parent 8685e9f2d1
commit fb80bc10ae
24 changed files with 4338 additions and 2978 deletions
--- a/s3/replica_client.go
+++ b/s3/replica_client.go
@@ -0,0 +1,746 @@
+package s3
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"path"
+	"sync"
+	"time"
+
+	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/aws/awserr"
+	"github.com/aws/aws-sdk-go/aws/credentials"
+	"github.com/aws/aws-sdk-go/aws/defaults"
+	"github.com/aws/aws-sdk-go/aws/session"
+	"github.com/aws/aws-sdk-go/service/s3"
+	"github.com/aws/aws-sdk-go/service/s3/s3manager"
+	"github.com/benbjohnson/litestream"
+	"github.com/benbjohnson/litestream/internal"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+	"golang.org/x/sync/errgroup"
+)
+
+// MaxKeys is the number of keys S3 can operate on per batch.
+const MaxKeys = 1000
+
+// DefaultRegion is the region used if one is not specified.
+const DefaultRegion = "us-east-1"
+
+var _ litestream.ReplicaClient = (*ReplicaClient)(nil)
+
+// ReplicaClient is a client for writing snapshots & WAL segments to disk.
+type ReplicaClient struct {
+	mu       sync.Mutex
+	s3       *s3.S3 // s3 service
+	uploader *s3manager.Uploader
+
+	// AWS authentication keys.
+	AccessKeyID     string
+	SecretAccessKey string
+
+	// S3 bucket information
+	Region         string
+	Bucket         string
+	Path           string
+	Endpoint       string
+	ForcePathStyle bool
+	SkipVerify     bool
+}
+
+// NewReplicaClient returns a new instance of ReplicaClient.
+func NewReplicaClient() *ReplicaClient {
+	return &ReplicaClient{}
+}
+
+// Type returns "s3" as the client type.
+func (c *ReplicaClient) Type() string {
+	return "s3"
+}
+
+// GenerationsDir returns the path to a generation root directory.
+func (c *ReplicaClient) GenerationsDir() string {
+	return path.Join(c.Path, "generations")
+}
+
+// GenerationDir returns the path to a generation's root directory.
+func (c *ReplicaClient) GenerationDir(generation string) (string, error) {
+	dir := c.GenerationsDir()
+	if generation == "" {
+		return "", fmt.Errorf("generation required")
+	}
+	return path.Join(dir, generation), nil
+}
+
+// SnapshotsDir returns the path to a generation's snapshot directory.
+func (c *ReplicaClient) SnapshotsDir(generation string) (string, error) {
+	dir, err := c.GenerationDir(generation)
+	if err != nil {
+		return "", err
+	}
+	return path.Join(dir, "snapshots"), nil
+}
+
+// SnapshotPath returns the path to an uncompressed snapshot file.
+func (c *ReplicaClient) SnapshotPath(generation string, index int) (string, error) {
+	dir, err := c.SnapshotsDir(generation)
+	if err != nil {
+		return "", err
+	}
+	return path.Join(dir, litestream.FormatSnapshotPath(index)), nil
+}
+
+// WALDir returns the path to a generation's WAL directory
+func (c *ReplicaClient) WALDir(generation string) (string, error) {
+	dir, err := c.GenerationDir(generation)
+	if err != nil {
+		return "", err
+	}
+	return path.Join(dir, "wal"), nil
+}
+
+// WALSegmentPath returns the path to a WAL segment file.
+func (c *ReplicaClient) WALSegmentPath(generation string, index int, offset int64) (string, error) {
+	dir, err := c.WALDir(generation)
+	if err != nil {
+		return "", err
+	}
+	return path.Join(dir, litestream.FormatWALSegmentPath(index, offset)), nil
+}
+
+// Init initializes the connection to S3. No-op if already initialized.
+func (c *ReplicaClient) Init(ctx context.Context) (err error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if c.s3 != nil {
+		return nil
+	}
+
+	// Look up region if not specified and no endpoint is used.
+	// Endpoints are typically used for non-S3 object stores and do not
+	// necessarily require a region.
+	region := c.Region
+	if region == "" {
+		if c.Endpoint == "" {
+			if region, err = c.findBucketRegion(ctx, c.Bucket); err != nil {
+				return fmt.Errorf("cannot lookup bucket region: %w", err)
+			}
+		} else {
+			region = DefaultRegion // default for non-S3 object stores
+		}
+	}
+
+	// Create new AWS session.
+	config := c.config()
+	if region != "" {
+		config.Region = aws.String(region)
+	}
+	sess, err := session.NewSession(config)
+	if err != nil {
+		return fmt.Errorf("cannot create aws session: %w", err)
+	}
+	c.s3 = s3.New(sess)
+	c.uploader = s3manager.NewUploader(sess)
+	return nil
+}
+
+// config returns the AWS configuration. Uses the default credential chain
+// unless a key/secret are explicitly set.
+func (c *ReplicaClient) config() *aws.Config {
+	config := defaults.Get().Config
+	if c.AccessKeyID != "" || c.SecretAccessKey != "" {
+		config.Credentials = credentials.NewStaticCredentials(c.AccessKeyID, c.SecretAccessKey, "")
+	}
+	if c.Endpoint != "" {
+		config.Endpoint = aws.String(c.Endpoint)
+	}
+	if c.ForcePathStyle {
+		config.S3ForcePathStyle = aws.Bool(c.ForcePathStyle)
+	}
+	if c.SkipVerify {
+		config.HTTPClient = &http.Client{Transport: &http.Transport{
+			TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
+		}}
+	}
+
+	return config
+}
+
+func (c *ReplicaClient) findBucketRegion(ctx context.Context, bucket string) (string, error) {
+	// Connect to US standard region to fetch info.
+	config := c.config()
+	config.Region = aws.String(DefaultRegion)
+	sess, err := session.NewSession(config)
+	if err != nil {
+		return "", err
+	}
+
+	// Fetch bucket location, if possible. Must be bucket owner.
+	// This call can return a nil location which means it's in us-east-1.
+	if out, err := s3.New(sess).GetBucketLocation(&s3.GetBucketLocationInput{
+		Bucket: aws.String(bucket),
+	}); err != nil {
+		return "", err
+	} else if out.LocationConstraint != nil {
+		return *out.LocationConstraint, nil
+	}
+	return DefaultRegion, nil
+}
+
+// Generations returns a list of available generation names.
+func (c *ReplicaClient) Generations(ctx context.Context) ([]string, error) {
+	if err := c.Init(ctx); err != nil {
+		return nil, err
+	}
+
+	var generations []string
+	if err := c.s3.ListObjectsPagesWithContext(ctx, &s3.ListObjectsInput{
+		Bucket:    aws.String(c.Bucket),
+		Prefix:    aws.String(c.GenerationsDir() + "/"),
+		Delimiter: aws.String("/"),
+	}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
+		operationTotalCounterVec.WithLabelValues("LIST").Inc()
+
+		for _, prefix := range page.CommonPrefixes {
+			name := path.Base(*prefix.Prefix)
+			if !litestream.IsGenerationName(name) {
+				continue
+			}
+			generations = append(generations, name)
+		}
+		return true
+	}); err != nil {
+		return nil, err
+	}
+
+	return generations, nil
+}
+
+// DeleteGeneration deletes all snapshots & WAL segments within a generation.
+func (c *ReplicaClient) DeleteGeneration(ctx context.Context, generation string) error {
+	if err := c.Init(ctx); err != nil {
+		return err
+	}
+
+	dir, err := c.GenerationDir(generation)
+	if err != nil {
+		return fmt.Errorf("cannot determine generation directory path: %w", err)
+	}
+
+	// Collect all files for the generation.
+	var objIDs []*s3.ObjectIdentifier
+	if err := c.s3.ListObjectsPagesWithContext(ctx, &s3.ListObjectsInput{
+		Bucket: aws.String(c.Bucket),
+		Prefix: aws.String(dir),
+	}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
+		operationTotalCounterVec.WithLabelValues("LIST").Inc()
+
+		for _, obj := range page.Contents {
+			objIDs = append(objIDs, &s3.ObjectIdentifier{Key: obj.Key})
+		}
+		return true
+	}); err != nil {
+		return err
+	}
+
+	// Delete all files in batches.
+	for len(objIDs) > 0 {
+		n := MaxKeys
+		if len(objIDs) < n {
+			n = len(objIDs)
+		}
+
+		if _, err := c.s3.DeleteObjectsWithContext(ctx, &s3.DeleteObjectsInput{
+			Bucket: aws.String(c.Bucket),
+			Delete: &s3.Delete{Objects: objIDs[:n], Quiet: aws.Bool(true)},
+		}); err != nil {
+			return err
+		}
+		operationTotalCounterVec.WithLabelValues("DELETE").Inc()
+
+		objIDs = objIDs[n:]
+	}
+
+	// log.Printf("%s(%s): retainer: deleting generation: %s", r.db.Path(), r.Name(), generation)
+
+	return nil
+}
+
+// Snapshots returns an iterator over all available snapshots for a generation.
+func (c *ReplicaClient) Snapshots(ctx context.Context, generation string) (litestream.SnapshotIterator, error) {
+	if err := c.Init(ctx); err != nil {
+		return nil, err
+	}
+	return newSnapshotIterator(ctx, c, generation), nil
+}
+
+// WriteSnapshot writes LZ4 compressed data from rd into a file on disk.
+func (c *ReplicaClient) WriteSnapshot(ctx context.Context, generation string, index int, rd io.Reader) (info litestream.SnapshotInfo, err error) {
+	if err := c.Init(ctx); err != nil {
+		return info, err
+	}
+
+	key, err := c.SnapshotPath(generation, index)
+	if err != nil {
+		return info, fmt.Errorf("cannot determine snapshot path: %w", err)
+	}
+	startTime := time.Now()
+
+	rc := internal.NewReadCounter(rd)
+	if _, err := c.uploader.UploadWithContext(ctx, &s3manager.UploadInput{
+		Bucket: aws.String(c.Bucket),
+		Key:    aws.String(key),
+		Body:   rc,
+	}); err != nil {
+		return info, err
+	}
+
+	operationTotalCounterVec.WithLabelValues("PUT").Inc()
+	operationBytesCounterVec.WithLabelValues("PUT").Add(float64(rc.N()))
+
+	// log.Printf("%s(%s): snapshot: creating %s/%08x t=%s", r.db.Path(), r.Name(), generation, index, time.Since(startTime).Truncate(time.Millisecond))
+
+	return litestream.SnapshotInfo{
+		Generation: generation,
+		Index:      index,
+		Size:       rc.N(),
+		CreatedAt:  startTime.UTC(),
+	}, nil
+}
+
+// SnapshotReader returns a reader for snapshot data at the given generation/index.
+func (c *ReplicaClient) SnapshotReader(ctx context.Context, generation string, index int) (io.ReadCloser, error) {
+	if err := c.Init(ctx); err != nil {
+		return nil, err
+	}
+
+	key, err := c.SnapshotPath(generation, index)
+	if err != nil {
+		return nil, fmt.Errorf("cannot determine snapshot path: %w", err)
+	}
+
+	out, err := c.s3.GetObjectWithContext(ctx, &s3.GetObjectInput{
+		Bucket: aws.String(c.Bucket),
+		Key:    aws.String(key),
+	})
+	if isNotExists(err) {
+		return nil, os.ErrNotExist
+	} else if err != nil {
+		return nil, err
+	}
+	operationTotalCounterVec.WithLabelValues("GET").Inc()
+	operationBytesCounterVec.WithLabelValues("GET").Add(float64(*out.ContentLength))
+
+	return out.Body, nil
+}
+
+// DeleteSnapshot deletes a snapshot with the given generation & index.
+func (c *ReplicaClient) DeleteSnapshot(ctx context.Context, generation string, index int) error {
+	if err := c.Init(ctx); err != nil {
+		return err
+	}
+
+	key, err := c.SnapshotPath(generation, index)
+	if err != nil {
+		return fmt.Errorf("cannot determine snapshot path: %w", err)
+	}
+
+	if _, err := c.s3.DeleteObjectsWithContext(ctx, &s3.DeleteObjectsInput{
+		Bucket: aws.String(c.Bucket),
+		Delete: &s3.Delete{Objects: []*s3.ObjectIdentifier{{Key: &key}}, Quiet: aws.Bool(true)},
+	}); err != nil {
+		return err
+	}
+
+	operationTotalCounterVec.WithLabelValues("DELETE").Inc()
+	return nil
+}
+
+// WALSegments returns an iterator over all available WAL files for a generation.
+func (c *ReplicaClient) WALSegments(ctx context.Context, generation string) (litestream.WALSegmentIterator, error) {
+	if err := c.Init(ctx); err != nil {
+		return nil, err
+	}
+	return newWALSegmentIterator(ctx, c, generation), nil
+}
+
+// WriteWALSegment writes LZ4 compressed data from rd into a file on disk.
+func (c *ReplicaClient) WriteWALSegment(ctx context.Context, pos litestream.Pos, rd io.Reader) (info litestream.WALSegmentInfo, err error) {
+	if err := c.Init(ctx); err != nil {
+		return info, err
+	}
+
+	key, err := c.WALSegmentPath(pos.Generation, pos.Index, pos.Offset)
+	if err != nil {
+		return info, fmt.Errorf("cannot determine wal segment path: %w", err)
+	}
+	startTime := time.Now()
+
+	rc := internal.NewReadCounter(rd)
+	if _, err := c.uploader.UploadWithContext(ctx, &s3manager.UploadInput{
+		Bucket: aws.String(c.Bucket),
+		Key:    aws.String(key),
+		Body:   rc,
+	}); err != nil {
+		return info, err
+	}
+
+	operationTotalCounterVec.WithLabelValues("PUT").Inc()
+	operationBytesCounterVec.WithLabelValues("PUT").Add(float64(rc.N()))
+
+	return litestream.WALSegmentInfo{
+		Generation: pos.Generation,
+		Index:      pos.Index,
+		Offset:     pos.Offset,
+		Size:       rc.N(),
+		CreatedAt:  startTime.UTC(),
+	}, nil
+}
+
+// WALSegmentReader returns a reader for a section of WAL data at the given index.
+// Returns os.ErrNotExist if no matching index/offset is found.
+func (c *ReplicaClient) WALSegmentReader(ctx context.Context, pos litestream.Pos) (io.ReadCloser, error) {
+	if err := c.Init(ctx); err != nil {
+		return nil, err
+	}
+
+	key, err := c.WALSegmentPath(pos.Generation, pos.Index, pos.Offset)
+	if err != nil {
+		return nil, fmt.Errorf("cannot determine wal segment path: %w", err)
+	}
+
+	out, err := c.s3.GetObjectWithContext(ctx, &s3.GetObjectInput{
+		Bucket: aws.String(c.Bucket),
+		Key:    aws.String(key),
+	})
+	if isNotExists(err) {
+		return nil, os.ErrNotExist
+	} else if err != nil {
+		return nil, err
+	}
+	operationTotalCounterVec.WithLabelValues("GET").Inc()
+	operationBytesCounterVec.WithLabelValues("GET").Add(float64(*out.ContentLength))
+
+	return out.Body, nil
+}
+
+// DeleteWALSegments deletes WAL segments with at the given positions.
+func (c *ReplicaClient) DeleteWALSegments(ctx context.Context, a []litestream.Pos) error {
+	if err := c.Init(ctx); err != nil {
+		return err
+	}
+
+	objIDs := make([]*s3.ObjectIdentifier, MaxKeys)
+	for len(a) > 0 {
+		n := MaxKeys
+		if len(a) < n {
+			n = len(a)
+		}
+
+		// Generate a batch of object IDs for deleting the WAL segments.
+		for i, pos := range a[:n] {
+			key, err := c.WALSegmentPath(pos.Generation, pos.Index, pos.Offset)
+			if err != nil {
+				return fmt.Errorf("cannot determine wal segment path: %w", err)
+			}
+			objIDs[i] = &s3.ObjectIdentifier{Key: &key}
+		}
+
+		// Delete S3 objects in bulk.
+		if _, err := c.s3.DeleteObjectsWithContext(ctx, &s3.DeleteObjectsInput{
+			Bucket: aws.String(c.Bucket),
+			Delete: &s3.Delete{Objects: objIDs[:n], Quiet: aws.Bool(true)},
+		}); err != nil {
+			return err
+		}
+
+		operationTotalCounterVec.WithLabelValues("DELETE").Inc()
+
+		a = a[n:]
+	}
+
+	return nil
+}
+
+// DeleteAll deletes everything on the remote path. Mainly used for testing.
+func (c *ReplicaClient) DeleteAll(ctx context.Context) error {
+	if err := c.Init(ctx); err != nil {
+		return err
+	}
+
+	prefix := c.Path
+	if prefix != "" {
+		prefix += "/"
+	}
+
+	// Collect all files for the generation.
+	var objIDs []*s3.ObjectIdentifier
+	if err := c.s3.ListObjectsPagesWithContext(ctx, &s3.ListObjectsInput{
+		Bucket: aws.String(c.Bucket),
+		Prefix: aws.String(prefix),
+	}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
+		operationTotalCounterVec.WithLabelValues("LIST").Inc()
+
+		for _, obj := range page.Contents {
+			objIDs = append(objIDs, &s3.ObjectIdentifier{Key: obj.Key})
+		}
+		return true
+	}); err != nil {
+		return err
+	}
+
+	// Delete all files in batches.
+	for len(objIDs) > 0 {
+		n := MaxKeys
+		if len(objIDs) < n {
+			n = len(objIDs)
+		}
+
+		if _, err := c.s3.DeleteObjectsWithContext(ctx, &s3.DeleteObjectsInput{
+			Bucket: aws.String(c.Bucket),
+			Delete: &s3.Delete{Objects: objIDs[:n], Quiet: aws.Bool(true)},
+		}); err != nil {
+			return err
+		}
+		operationTotalCounterVec.WithLabelValues("DELETE").Inc()
+
+		objIDs = objIDs[n:]
+	}
+
+	return nil
+}
+
+type snapshotIterator struct {
+	client     *ReplicaClient
+	generation string
+
+	ch     chan litestream.SnapshotInfo
+	g      errgroup.Group
+	ctx    context.Context
+	cancel func()
+
+	info litestream.SnapshotInfo
+	err  error
+}
+
+func newSnapshotIterator(ctx context.Context, client *ReplicaClient, generation string) *snapshotIterator {
+	itr := &snapshotIterator{
+		client:     client,
+		generation: generation,
+		ch:         make(chan litestream.SnapshotInfo),
+	}
+
+	itr.ctx, itr.cancel = context.WithCancel(ctx)
+	itr.g.Go(itr.fetch)
+
+	return itr
+}
+
+// fetch runs in a separate goroutine to fetch pages of objects and stream them to a channel.
+func (itr *snapshotIterator) fetch() error {
+	defer close(itr.ch)
+
+	dir, err := itr.client.SnapshotsDir(itr.generation)
+	if err != nil {
+		return fmt.Errorf("cannot determine snapshot directory path: %w", err)
+	}
+
+	return itr.client.s3.ListObjectsPagesWithContext(itr.ctx, &s3.ListObjectsInput{
+		Bucket:    aws.String(itr.client.Bucket),
+		Prefix:    aws.String(dir + "/"),
+		Delimiter: aws.String("/"),
+	}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
+		operationTotalCounterVec.WithLabelValues("LIST").Inc()
+
+		for _, obj := range page.Contents {
+			key := path.Base(*obj.Key)
+			index, err := litestream.ParseSnapshotPath(key)
+			if err != nil {
+				continue
+			}
+
+			info := litestream.SnapshotInfo{
+				Generation: itr.generation,
+				Index:      index,
+				Size:       *obj.Size,
+				CreatedAt:  obj.LastModified.UTC(),
+			}
+
+			select {
+			case <-itr.ctx.Done():
+			case itr.ch <- info:
+			}
+		}
+		return true
+	})
+}
+
+func (itr *snapshotIterator) Close() (err error) {
+	err = itr.err
+
+	// Cancel context and wait for error group to finish.
+	itr.cancel()
+	if e := itr.g.Wait(); e != nil && err == nil {
+		err = e
+	}
+
+	return err
+}
+
+func (itr *snapshotIterator) Next() bool {
+	// Exit if an error has already occurred.
+	if itr.err != nil {
+		return false
+	}
+
+	// Return false if context was canceled or if there are no more snapshots.
+	// Otherwise fetch the next snapshot and store it on the iterator.
+	select {
+	case <-itr.ctx.Done():
+		return false
+	case info, ok := <-itr.ch:
+		if !ok {
+			return false
+		}
+		itr.info = info
+		return true
+	}
+}
+
+func (itr *snapshotIterator) Err() error { return itr.err }
+
+func (itr *snapshotIterator) Snapshot() litestream.SnapshotInfo {
+	return itr.info
+}
+
+type walSegmentIterator struct {
+	client     *ReplicaClient
+	generation string
+
+	ch     chan litestream.WALSegmentInfo
+	g      errgroup.Group
+	ctx    context.Context
+	cancel func()
+
+	info litestream.WALSegmentInfo
+	err  error
+}
+
+func newWALSegmentIterator(ctx context.Context, client *ReplicaClient, generation string) *walSegmentIterator {
+	itr := &walSegmentIterator{
+		client:     client,
+		generation: generation,
+		ch:         make(chan litestream.WALSegmentInfo),
+	}
+
+	itr.ctx, itr.cancel = context.WithCancel(ctx)
+	itr.g.Go(itr.fetch)
+
+	return itr
+}
+
+// fetch runs in a separate goroutine to fetch pages of objects and stream them to a channel.
+func (itr *walSegmentIterator) fetch() error {
+	defer close(itr.ch)
+
+	dir, err := itr.client.WALDir(itr.generation)
+	if err != nil {
+		return fmt.Errorf("cannot determine wal directory path: %w", err)
+	}
+
+	return itr.client.s3.ListObjectsPagesWithContext(itr.ctx, &s3.ListObjectsInput{
+		Bucket:    aws.String(itr.client.Bucket),
+		Prefix:    aws.String(dir + "/"),
+		Delimiter: aws.String("/"),
+	}, func(page *s3.ListObjectsOutput, lastPage bool) bool {
+		operationTotalCounterVec.WithLabelValues("LIST").Inc()
+
+		for _, obj := range page.Contents {
+			key := path.Base(*obj.Key)
+			index, offset, err := litestream.ParseWALSegmentPath(key)
+			if err != nil {
+				continue
+			}
+
+			info := litestream.WALSegmentInfo{
+				Generation: itr.generation,
+				Index:      index,
+				Offset:     offset,
+				Size:       *obj.Size,
+				CreatedAt:  obj.LastModified.UTC(),
+			}
+
+			select {
+			case <-itr.ctx.Done():
+				return false
+			case itr.ch <- info:
+			}
+		}
+		return true
+	})
+}
+
+func (itr *walSegmentIterator) Close() (err error) {
+	err = itr.err
+
+	// Cancel context and wait for error group to finish.
+	itr.cancel()
+	if e := itr.g.Wait(); e != nil && err == nil {
+		err = e
+	}
+
+	return err
+}
+
+func (itr *walSegmentIterator) Next() bool {
+	// Exit if an error has already occurred.
+	if itr.err != nil {
+		return false
+	}
+
+	// Return false if context was canceled or if there are no more segments.
+	// Otherwise fetch the next segment and store it on the iterator.
+	select {
+	case <-itr.ctx.Done():
+		return false
+	case info, ok := <-itr.ch:
+		if !ok {
+			return false
+		}
+		itr.info = info
+		return true
+	}
+}
+
+func (itr *walSegmentIterator) Err() error { return itr.err }
+
+func (itr *walSegmentIterator) WALSegment() litestream.WALSegmentInfo {
+	return itr.info
+}
+
+func isNotExists(err error) bool {
+	switch err := err.(type) {
+	case awserr.Error:
+		return err.Code() == `NoSuchKey`
+	default:
+		return false
+	}
+}
+
+// S3 metrics.
+var (
+	operationTotalCounterVec = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "litestream_s3_operation_total",
+		Help: "The number of S3 operations performed",
+	}, []string{"type"})
+
+	operationBytesCounterVec = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "litestream_s3_operation_bytes",
+		Help: "The number of bytes used by S3 operations",
+	}, []string{"type"})
+)