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backend: factor out connection limiting and parameter validation

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The SemaphoreBackend now uniformly enforces the limit of concurrent
backend operations. In addition, it unifies the parameter validation.

The List() methods no longer uses a semaphore. Restic already never runs
multiple list operations in parallel.

By managing the semaphore in a wrapper backend, the sections that hold a
semaphore token grow slightly. However, the main bottleneck is IO, so
this shouldn't make much of a difference.

The key insight that enables the SemaphoreBackend is that all of the
complex semaphore handling in `openReader()` still happens within the
original call to `Load()`. Thus, getting and releasing the semaphore
tokens can be refactored to happen directly in `Load()`. This eliminates
the need for wrapping the reader in `openReader()` to release the token.
This commit is contained in:
Michael Eischer
2023-04-07 23:02:35 +02:00
parent 8b5ab5b59f
commit 8e1e3844aa
13 changed files with 126 additions and 384 deletions
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26
internal/backend/azure/azure.go
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@@ -14,7 +14,6 @@ import (
"github.com/restic/restic/internal/backend"
"github.com/restic/restic/internal/backend/layout"
"github.com/restic/restic/internal/backend/sema"
"github.com/restic/restic/internal/debug"
"github.com/restic/restic/internal/errors"
"github.com/restic/restic/internal/restic"
@@ -26,7 +25,6 @@ import (
"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/bloberror"
"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blockblob"
azContainer "github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/container"
"github.com/cenkalti/backoff/v4"
)
// Backend stores data on an azure endpoint.
@@ -34,7 +32,6 @@ type Backend struct {
cfg Config
container *azContainer.Client
connections uint
sem sema.Semaphore
prefix string
listMaxItems int
layout.Layout
@@ -96,16 +93,10 @@ func open(cfg Config, rt http.RoundTripper) (*Backend, error) {
return nil, errors.New("no azure authentication information found")
}
sem, err := sema.New(cfg.Connections)
if err != nil {
return nil, err
}
be := &Backend{
container: client,
cfg: cfg,
connections: cfg.Connections,
sem: sem,
Layout: &layout.DefaultLayout{
Path: cfg.Prefix,
Join: path.Join,
@@ -186,14 +177,8 @@ func (be *Backend) Path() string {
// Save stores data in the backend at the handle.
func (be *Backend) Save(ctx context.Context, h restic.Handle, rd restic.RewindReader) error {
if err := h.Valid(); err != nil {
return backoff.Permanent(err)
}
objName := be.Filename(h)
be.sem.GetToken()
debug.Log("InsertObject(%v, %v)", be.cfg.AccountName, objName)
var err error
@@ -205,7 +190,6 @@ func (be *Backend) Save(ctx context.Context, h restic.Handle, rd restic.RewindRe
err = be.saveLarge(ctx, objName, rd)
}
be.sem.ReleaseToken()
return err
}
@@ -297,7 +281,6 @@ func (be *Backend) openReader(ctx context.Context, h restic.Handle, length int,
objName := be.Filename(h)
blockBlobClient := be.container.NewBlobClient(objName)
be.sem.GetToken()
resp, err := blockBlobClient.DownloadStream(ctx, &blob.DownloadStreamOptions{
Range: azblob.HTTPRange{
Offset: offset,
@@ -306,11 +289,10 @@ func (be *Backend) openReader(ctx context.Context, h restic.Handle, length int,
})
if err != nil {
be.sem.ReleaseToken()
return nil, err
}
return be.sem.ReleaseTokenOnClose(resp.Body, nil), err
return resp.Body, err
}
// Stat returns information about a blob.
@@ -318,9 +300,7 @@ func (be *Backend) Stat(ctx context.Context, h restic.Handle) (restic.FileInfo,
objName := be.Filename(h)
blobClient := be.container.NewBlobClient(objName)
be.sem.GetToken()
props, err := blobClient.GetProperties(ctx, nil)
be.sem.ReleaseToken()
if err != nil {
return restic.FileInfo{}, errors.Wrap(err, "blob.GetProperties")
@@ -338,9 +318,7 @@ func (be *Backend) Remove(ctx context.Context, h restic.Handle) error {
objName := be.Filename(h)
blob := be.container.NewBlobClient(objName)
be.sem.GetToken()
_, err := blob.Delete(ctx, &azblob.DeleteBlobOptions{})
be.sem.ReleaseToken()
if be.IsNotExist(err) {
return nil
@@ -368,9 +346,7 @@ func (be *Backend) List(ctx context.Context, t restic.FileType, fn func(restic.F
lister := be.container.NewListBlobsFlatPager(opts)
for lister.More() {
be.sem.GetToken()
resp, err := lister.NextPage(ctx)
be.sem.ReleaseToken()
if err != nil {
return err