writecache

Documentation

Overview

Package writecache implements write-cache for objects.

Write-cache has 2 components: 1. Key-value (bbolt) database for storing small objects. 2. Filesystem tree for storing big objects.

Flushing from the writecache to the main storage is done in the background. To make it possible to serve Read requests after the object was flushed, we maintain an LRU cache containing addresses of all the objects that could be safely deleted. The actual deletion is done during eviction from this cache.

Index

• Variables
• func Get(db *bbolt.DB, key []byte) ([]byte, error)
• func IterateDB(db *bbolt.DB, f func(oid.Address) error) error
• func OpenDB(p string, ro bool) (*bbolt.DB, error)
• type Cache
  • func New(opts ...Option) Cache
• type Info
• type IterationPrm
  • func (p *IterationPrm) WithHandler(f func([]byte) error)
  • func (p *IterationPrm) WithIgnoreErrors(ignore bool)
• type Option
  • func WithBlobstor(bs *blobstor.BlobStor) Option
  • func WithFlushWorkersCount(c int) Option
  • func WithLogger(log *logger.Logger) Option
  • func WithMaxBatchDelay(d time.Duration) Option
  • func WithMaxBatchSize(sz int) Option
  • func WithMaxCacheSize(sz uint64) Option
  • func WithMaxObjectSize(sz uint64) Option
  • func WithMetabase(db *meta.DB) Option
  • func WithNoSync(noSync bool) Option
  • func WithPath(path string) Option
  • func WithReportErrorFunc(f func(string, error)) Option
  • func WithSmallObjectSize(sz uint64) Option

Variables

var (
	// ErrBigObject is returned when object is too big to be placed in cache.
	ErrBigObject = errors.New("too big object")
	// ErrOutOfSpace is returned when there is no space left to put a new object.
	ErrOutOfSpace = errors.New("no space left in the write cache")
)

var ErrNoDefaultBucket = errors.New("no default bucket")

ErrNoDefaultBucket is returned by IterateDB when default bucket for objects is missing.

var ErrReadOnly = logicerr.New("write-cache is in read-only mode")

ErrReadOnly is returned when Put/Write is performed in a read-only mode.

Functions

func Get

func Get(db *bbolt.DB, key []byte) ([]byte, error)

Get fetches object from the underlying database. Key should be a stringified address.

Returns an error of type apistatus.ObjectNotFound if the requested object is missing in db.

func IterateDB

func IterateDB(db *bbolt.DB, f func(oid.Address) error) error

IterateDB iterates over all objects stored in bbolt.DB instance and passes them to f until error return. It is assumed that db is an underlying database of some WriteCache instance.

Returns ErrNoDefaultBucket if there is no default bucket in db.

DB must not be nil and should be opened.

func OpenDB

func OpenDB(p string, ro bool) (*bbolt.DB, error)

OpenDB opens BoltDB instance for write-cache. Opens in read-only mode if ro is true.

Types

type Cache

type Cache interface {
	Get(address oid.Address) (*object.Object, error)
	Head(oid.Address) (*object.Object, error)
	// Delete removes object referenced by the given oid.Address from the
	// Cache. Returns any error encountered that prevented the object to be
	// removed.
	//
	// Returns apistatus.ObjectNotFound if object is missing in the Cache.
	// Returns ErrReadOnly if the Cache is currently in the read-only mode.
	Delete(oid.Address) error
	Iterate(IterationPrm) error
	Put(common.PutPrm) (common.PutRes, error)
	SetMode(mode.Mode) error
	SetLogger(*logger.Logger)
	DumpInfo() Info
	Flush(bool) error

	Init() error
	Open(readOnly bool) error
	Close() error
}

Cache represents write-cache for objects.

func New

func New(opts ...Option) Cache

New creates new writecache instance.

type Info

type Info struct {
	// Full path to the write-cache.
	Path string
}

Info groups the information about write-cache.

type IterationPrm

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

IterationPrm contains iteration parameters.

func (*IterationPrm) WithHandler

func (p *IterationPrm) WithHandler(f func([]byte) error)

WithHandler sets a callback to be executed on every object.

func (*IterationPrm) WithIgnoreErrors

func (p *IterationPrm) WithIgnoreErrors(ignore bool)

WithIgnoreErrors sets a flag indicating that errors should be ignored.

type Option

type Option func(*options)

Option represents write-cache configuration option.

func WithBlobstor

func WithBlobstor(bs *blobstor.BlobStor) Option

WithBlobstor sets main object storage.

func WithFlushWorkersCount

func WithFlushWorkersCount(c int) Option

func WithLogger

func WithLogger(log *logger.Logger) Option

WithLogger sets logger.

func WithMaxBatchDelay

func WithMaxBatchDelay(d time.Duration) Option

WithMaxBatchDelay sets max batch delay for the small object database.

func WithMaxBatchSize

func WithMaxBatchSize(sz int) Option

WithMaxBatchSize sets max batch size for the small object database.

func WithMaxCacheSize

func WithMaxCacheSize(sz uint64) Option

WithMaxCacheSize sets maximum write-cache size in bytes.

func WithMaxObjectSize

func WithMaxObjectSize(sz uint64) Option

WithMaxObjectSize sets maximum object size to be stored in write-cache.

func WithMetabase

func WithMetabase(db *meta.DB) Option

WithMetabase sets metabase.

func WithNoSync

func WithNoSync(noSync bool) Option

WithNoSync sets an option to allow returning to caller on PUT before write is persisted. Note, that we use this flag for FSTree only and DO NOT use it for a bolt DB because we cannot yet properly handle the corrupted database during the startup. This SHOULD NOT be relied upon and may be changed in future.

func WithPath

func WithPath(path string) Option

WithPath sets path to writecache db.

func WithReportErrorFunc

func WithReportErrorFunc(f func(string, error)) Option

WithReportErrorFunc sets error reporting function.

func WithSmallObjectSize

func WithSmallObjectSize(sz uint64) Option

WithSmallObjectSize sets maximum object size to be stored in write-cache.