persistence

Documentation

Overview

Package persistence defines interfaces and tests for storing log state.

Index

• type LogStatePersistence
• type LogStateReadOps
• type LogStateWriteOps

Types

type LogStatePersistence

type LogStatePersistence interface {
	// Init sets up the persistence layer. This should be idempotent,
	// and will be called once per process startup.
	Init() error

	// Logs returns the IDs of all logs that have checkpoints that can
	// be read.
	Logs() ([]string, error)

	// ReadOps returns read-only operations for the given log ID.
	// TODO(al): This method MUST return a valid LogStateReadOps even if
	// the logID is unknown, otherwise WriteOps will never be called
	// and the TOFU checkpoint will never be written.
	ReadOps(logID string) (LogStateReadOps, error)

	// WriteOps shows intent to write data for the given logID. The
	// returned operations must have Close() called when the intent
	// is complete.
	// There is no requirement that the ID is present in Logs(); if
	// the ID is not there and this operation succeeds in committing
	// a checkpoint, then Logs() will return the new ID afterwards.
	WriteOps(logID string) (LogStateWriteOps, error)
}

LogStatePersistence is a handle on persistent storage for log state.

type LogStateReadOps

type LogStateReadOps interface {
	// GetLatest returns the latest checkpoint.
	// If no checkpoint exists, it must return codes.NotFound.
	GetLatest() ([]byte, error)
}

LogStateReadOps allows the data about a single log to be read.

type LogStateWriteOps

type LogStateWriteOps interface {
	LogStateReadOps

	// Set sets a new checkpoint for the log, committing the state to persistence.
	// After this call, only Close() should be called on this object.
	Set(checkpointRaw []byte) error

	// Terminates the write operation, freeing all resources.
	// This method MUST be called.
	Close() error
}

LogStateWriteOps allows data about a single log to be read and written in an ACID transaction. This naturally mirrors a DB transaction, but implementations don't need to use a database. Note that Close() must be called whenever these operations are no longer needed.