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Published: May 15, 2019 License: MIT Imports: 32 Imported by: 0



Package fragment is concerned with the mapping of journal offsets to protocol.Fragments, to corresponding local or remote journal content. It provides implementation for:

  • Interacting with remote fragment stores.
  • Indexing local and remote Fragments (see Index).
  • The construction of new Fragments from a replication stream (see Spool).
  • The persisting of constructed Fragments to remote stores (see Persister).



This section is empty.


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var FileSystemStoreRoot = "/dev/null/invalid/example/path/to/store"

FileSystemStoreRoot is the filesystem path which roots fragment ContentPaths of a file:// fragment store. It must be set at program startup prior to use.


func List

func List(ctx context.Context, store pb.FragmentStore, name pb.Journal, callback func(pb.Fragment)) error

List Fragments of the FragmentStore for a given journal. |callback| is invoked with each listed Fragment, and any returned error aborts the listing.

func Open

func Open(ctx context.Context, fragment pb.Fragment) (io.ReadCloser, error)

Open a Reader of the Fragment on the store. The returned ReadCloser does not perform any applicable client-side decompression, but does request server decompression in the case of GZIP_OFFLOAD_DECOMPRESSION.

func Persist

func Persist(ctx context.Context, spool Spool) error

Persist a Spool to its store. If the Spool Fragment is already present, this is a no-op. If the Spool has not been compressed incrementally, it will be compressed before being persisted.

func Remove

func Remove(ctx context.Context, fragment pb.Fragment) error

Remove |fragment| from its BackingStore.

func SignGetURL

func SignGetURL(fragment pb.Fragment, d time.Duration) (string, error)

SignGetURL returns a URL authenticating the bearer to perform a GET operation of the Fragment for the provided Duration from the current time.


type CoverSet

type CoverSet []Fragment

CoverSet maintains Fragments ordered on |Begin| and |End|, with the invariant that no Fragment is fully overlapped by another Fragment in the set (though it may be overlapped by a combination of other Fragments). Intuitively, CoverSet represents the set of offsets which are "covered" by a collection of Fragments, and is able to map, for each byte offset, a "best" covering Fragment. It employs a heuristic of preferring larger fragments (and will replace spans of overlapped smaller fragments). An implication of its invariant is that no two Fragments have the same |Begin| or |End| (as that would imply an overlap). Both are monotonically increasing in the set: set[0].Begin represents the minimum offset, and set[len(set)-1].End represents the maximum offset.

func CoverSetDifference

func CoverSetDifference(a, b CoverSet) CoverSet

CoverSetDifference returns the subset of Fragments in |a| which cover byte offsets not also covered by Fragments in |b|.

func WalkAllStores

func WalkAllStores(ctx context.Context, name pb.Journal, stores []pb.FragmentStore) (CoverSet, error)

WalkAllStores enumerates Fragments from each of |stores| into the returned CoverSet, or returns an encountered error.

func (CoverSet) Add

func (s CoverSet) Add(fragment Fragment) (CoverSet, bool)

Add the Fragment to the CoverSet. The CoverSet is returned, along with an indication of whether an offset span was updated to reflect Fragment. All updates occur in-place.

func (CoverSet) BeginOffset

func (s CoverSet) BeginOffset() int64

BeginOffset returns the first (lowest) Begin offset of any Fragment in the CoverSet.

func (CoverSet) EndOffset

func (s CoverSet) EndOffset() int64

EndOffset returns the last (largest) End offset of any Fragment in the set.

func (CoverSet) LongestOverlappingFragment

func (s CoverSet) LongestOverlappingFragment(offset int64) (ind int, found bool)

LongestOverlappingFragment finds and returns the index |ind| of the Fragment covering |offset| which also has the most content following |offset|. If no fragment covers |offset|, the index of the next Fragment beginning after |offset| is returned (which may be beyond the current CoverSet range). |found| indicates whether an overlapping Fragment was found.

type File

type File interface {

File is the subset of os.File used in backing Fragments with local files.

type Fragment

type Fragment struct {
	// Local uncompressed file of the Fragment, or nil iff the Fragment is remote.
	File File

Fragment wraps the protocol.Fragment type with a nil-able backing local File.

type Index

type Index struct {
	// contains filtered or unexported fields

Index maintains a queryable index of local and remote journal Fragments.

func NewIndex

func NewIndex(ctx context.Context) *Index

NewIndex returns a new, empty Index.

func (*Index) EndOffset

func (fi *Index) EndOffset() int64

EndOffset returns the last (largest) End offset in the index.

func (*Index) Inspect

func (fi *Index) Inspect(callback func(CoverSet) error) error

Inspect will call |callback| with a CoverSet represeting a snapshot of all the fragments in the index. While |callback| is executing there will be no changes to the fragment set of the index.

func (*Index) Query

func (fi *Index) Query(ctx context.Context, req *pb.ReadRequest) (*pb.ReadResponse, File, error)

Query the Index for a Fragment matching the ReadRequest.

func (*Index) ReplaceRemote

func (fi *Index) ReplaceRemote(set CoverSet)

ReplaceRemote replaces all remote Fragments in the index with |set|.

func (*Index) SpoolCommit

func (fi *Index) SpoolCommit(frag Fragment)

SpoolCommit adds local Spool Fragment |frag| to the index.

func (*Index) WaitForFirstRemoteRefresh

func (fi *Index) WaitForFirstRemoteRefresh(ctx context.Context) error

WaitForFirstRemoteRefresh blocks until ReplaceRemote has been called at least one time, or until the context is cancelled.

type Persister

type Persister struct {
	// contains filtered or unexported fields

func NewPersister

func NewPersister(ks *keyspace.KeySpace) *Persister

NewPersister returns an empty, initialized Persister.

func (*Persister) Finish

func (p *Persister) Finish()

func (*Persister) Serve

func (p *Persister) Serve()

func (*Persister) SpoolComplete

func (p *Persister) SpoolComplete(spool Spool, primary bool)

type Spool

type Spool struct {
	// Fragment at time of last commit.
	// FirstAppendTime is the timestamp of the first append of the current fragment.
	FirstAppendTime time.Time
	// contains filtered or unexported fields

Spool is a Fragment which is in the process of being created, backed by a local *os.File. As commits occur and the file extent is updated, the Spool Fragment is also updated to reflect the new committed extent. At all times, the Spool Fragment is a consistent, valid Fragment.

func NewSpool

func NewSpool(journal pb.Journal, observer SpoolObserver) Spool

NewSpool returns an empty Spool of |journal|.

func (*Spool) Apply

func (s *Spool) Apply(r *pb.ReplicateRequest, primary bool) (pb.ReplicateResponse, error)

Apply the ReplicateRequest to the Spool, returning any encountered error.

func (*Spool) MustApply

func (s *Spool) MustApply(r *pb.ReplicateRequest)

MustApply applies the ReplicateRequest, and panics if a !OK status is returned or error occurs. MustApply is a convenience for cases such as rollbacks, where the request is derived from the Spool itself and cannot reasonably fail.

func (*Spool) Next

func (s *Spool) Next() pb.Fragment

Next returns the next Fragment which can be committed by the Spool.

func (Spool) String

func (s Spool) String() string

String returns a debugging representation of the Spool.

type SpoolObserver

type SpoolObserver interface {
	// SpoolCommit is called when the Spool Fragment is extended.
	// SpoolComplete is called when the Spool has been completed.
	SpoolComplete(_ Spool, primary bool)

SpoolObserver is notified of important events in the Spool lifecycle.

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