Documentation

Overview

    Package fragment is a broker-only package concerned with the mapping of journal offsets to protocol.Fragments, and from there to corresponding local or remote journal content.

    It implements file-like operations over the FragmentStore schemes supported by Gazette, such as listing, opening, signing, persisting, and removing fragments. See FileStoreConfig, S3StoreConfig, and GSStoreConfig for further configuration of store operations.

    The package implements a Fragment wrapper type which composes a protocol.Fragment with an open file descriptor, and an Index over local or remote Fragments which maps a journal offset to a best-covering Fragment.

    Spool is a Fragment which is in the process of being constructed from an ongoing broker Replicate RPC. It is the transactional "memory" of brokers which are participating in the replication of a journal. Once closed, or "rolled", a Spool Fragment is persisted to its configured FragmentStore by a Persister.

    Index

    Constants

    This section is empty.

    Variables

    View Source
    var FileSystemStoreRoot = "/dev/null/must/configure/file/store/root"

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

      Functions

      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, spec *pb.JournalSpec) error

            Persist a Spool to the JournalSpec's 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.

                Types

                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 {
                              	io.ReaderAt
                              	io.Seeker
                              	io.WriterAt
                              	io.Writer
                              	io.Closer
                              }

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

                                type FileStoreConfig

                                type FileStoreConfig struct {
                                	RewriterConfig
                                }

                                  FileStoreConfig configures a Fragment store of the "file://" scheme. It is initialized from parsed URL parameters of the pb.FragmentStore.

                                  type Fragment

                                  type Fragment struct {
                                  	protocol.Fragment
                                  	// 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 GSStoreConfig

                                    type GSStoreConfig struct {
                                    	RewriterConfig
                                    	// contains filtered or unexported fields
                                    }

                                      GSStoreConfig configures a Fragment store of the "gs://" scheme. It is initialized from parsed URL parameters of the pb.FragmentStore.

                                      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) FirstRefreshCh

                                            func (fi *Index) FirstRefreshCh() <-chan struct{}

                                              FirstRefreshCh returns a channel which signals if the Index as been refreshed with a remote store(s) listing at least once.

                                              func (*Index) Inspect

                                              func (fi *Index) Inspect(ctx context.Context, callback func(CoverSet) error) error

                                                Inspect invokes the callback with a snapshot of all fragments in the Index. The callback must not modify the CoverSet, and during callback invocation no changes will be made to it. If an initial refresh of remote fragment store(s) hasn't yet been applied, Inspect will first block until it does (or context cancellation).

                                                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.

                                                      type Persister

                                                      type Persister struct {
                                                      	// contains filtered or unexported fields
                                                      }

                                                        Persister asynchronously persists completed Fragments to their backing pb.FragmentStore.

                                                        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 RewriterConfig

                                                          type RewriterConfig struct {
                                                          	// Find is the string to replace in the unmodified journal name.
                                                          	Find string
                                                          	// Replace is the string with which Find is replaced in the constructed store path.
                                                          	Replace string
                                                          }

                                                            RewriterConfig rewrites the path under which journal fragments are stored by finding and replacing a portion of the journal's name in the final constructed path. Its use is uncommon and not recommended, but it can help in the implementation of new journal naming taxonomies which don't disrupt journal fragments that are already written.

                                                            var cfg = RewriterConfig{
                                                                Replace: "/old-path/page-views/
                                                                Find:    "/bar/v1/page-views/",
                                                            }
                                                            // Remaps journal name => fragment store URL:
                                                            //  "/foo/bar/v1/page-views/part-000" => "s3://my-bucket/foo/old-path/page-views/part-000" // Matched.
                                                            //  "/foo/bar/v2/page-views/part-000" => "s3://my-bucket/foo/bar/v2/page-views/part-000"   // Not matched.
                                                            

                                                            type S3StoreConfig

                                                            type S3StoreConfig struct {
                                                            	RewriterConfig
                                                            	// AWS Profile to extract credentials from the shared credentials file.
                                                            	// For details, see:
                                                            	//   https://aws.amazon.com/blogs/security/a-new-and-standardized-way-to-manage-credentials-in-the-aws-sdks/
                                                            	// If empty, the default credentials are used.
                                                            	Profile string
                                                            	// Endpoint to connect to S3. If empty, the default S3 service is used.
                                                            	Endpoint string
                                                            	// ACL applied when persisting new fragments. By default, this is
                                                            	// s3.ObjectCannedACLBucketOwnerFullControl.
                                                            	ACL string
                                                            	// Storage class applied when persisting new fragments. By default,
                                                            	// this is s3.ObjectStorageClassStandard.
                                                            	StorageClass string
                                                            	// SSE is the server-side encryption type to be applied (eg, "AES256").
                                                            	// By default, encryption is not used.
                                                            	SSE string
                                                            	// contains filtered or unexported fields
                                                            }

                                                              S3StoreConfig configures a Fragment store of the "s3://" scheme. It is initialized from parsed URL parameters of the pb.FragmentStore.

                                                              type Spool

                                                              type Spool struct {
                                                              	// Fragment at time of last commit.
                                                              	Fragment
                                                              	// FirstAppendTime is the UTC Time of the first commit of the Spool Fragment.
                                                              	FirstAppendTime time.Time
                                                              	// Registers of the journal.
                                                              	Registers pb.LabelSet
                                                              	// 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.
                                                                          	SpoolCommit(Fragment)
                                                                          	// SpoolComplete is called when the Spool has been completed.
                                                                          	SpoolComplete(_ Spool, primary bool)
                                                                          }

                                                                            SpoolObserver is notified of important events in the Spool lifecycle.