Documentation ¶
Overview ¶
Package writecache implements write-cache for objects.
It contains in-memory cache of fixed size and underlying database (usually on SSD) for storing small objects. There are 3 places where object can be: 1. In-memory cache. 2. On-disk cache DB. 3. Main storage (blobstor).
There are 2 types of background jobs:
- Persisting objects from in-memory cache to database.
- Flushing objects from database to blobstor. On flushing object address is put in in-memory LRU cache. The actual deletion from the DB is done when object is evicted from this cache.
Putting objects to the main storage is done by multiple workers. Some of them prioritize flushing items, others prioritize putting new objects. The current ration is 50/50. This helps to make some progress even under load.
Index ¶
- Variables
- func Get(db *bbolt.DB, key []byte) ([]byte, error)
- func IsErrNotFound(err error) bool
- func IterateDB(db *bbolt.DB, f func(oid.Address) error) error
- func OpenDB(p string, ro bool) (*bbolt.DB, error)
- type Cache
- type Info
- type IterationPrm
- type ObjectCounters
- type Option
- func WithBlobstor(bs *blobstor.BlobStor) Option
- func WithFlushWorkersCount(c int) Option
- func WithLogger(log *zap.Logger) Option
- func WithMaxBatchDelay(d time.Duration) Option
- func WithMaxBatchSize(sz int) Option
- func WithMaxCacheSize(sz uint64) Option
- func WithMaxMemSize(sz uint64) Option
- func WithMaxObjectSize(sz uint64) Option
- func WithMetabase(db *meta.DB) Option
- func WithObjectCounters(v ObjectCounters) Option
- func WithPath(path string) Option
- func WithSmallObjectSize(sz uint64) Option
Constants ¶
This section is empty.
Variables ¶
var ErrBigObject = errors.New("too big object")
ErrBigObject is returned when object is too big to be placed in cache.
var ErrNoDefaultBucket = errors.New("no default bucket")
ErrNoDefaultBucket is returned by IterateDB when default bucket for objects is missing.
var ErrReadOnly = errors.New("write-cache is in read-only mode")
ErrReadOnly is returned when Put/Write is performed in a read-only mode.
Functions ¶
func Get ¶ added in v0.26.0
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 IsErrNotFound ¶ added in v0.28.0
IsErrNotFound checks if error returned by Cache Get/Head/Delete method corresponds to missing object.
func IterateDB ¶ added in v0.26.0
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.
Types ¶
type Cache ¶
type Cache interface { Get(address oid.Address) (*object.Object, error) Head(oid.Address) (*object.Object, error) Delete(oid.Address) error Iterate(IterationPrm) error Put(*object.Object) error SetMode(mode.Mode) error SetLogger(*zap.Logger) DumpInfo() Info Init() error Open(readOnly bool) error Close() error }
Cache represents write-cache for objects.
type Info ¶ added in v0.27.2
type Info struct { // Full path to the write-cache. Path string }
Info groups the information about write-cache.
type IterationPrm ¶ added in v0.27.5
type IterationPrm struct {
// contains filtered or unexported fields
}
IterationPrm contains iteration parameters.
func (*IterationPrm) WithHandler ¶ added in v0.27.5
func (p *IterationPrm) WithHandler(f func([]byte) error)
WithHandler sets a callback to be executed on every object.
func (*IterationPrm) WithIgnoreErrors ¶ added in v0.27.5
func (p *IterationPrm) WithIgnoreErrors(ignore bool)
WithIgnoreErrors sets a flag indicating that errors should be ignored.
type ObjectCounters ¶ added in v0.25.0
type ObjectCounters interface { // Increments number of objects saved in DB. IncDB() // Decrements number of objects saved in DB. DecDB() // Returns number of objects saved in DB. DB() uint64 // Increments number of objects saved in FSTree. IncFS() // Decrements number of objects saved in FSTree. DecFS() // Returns number of objects saved in FSTree. FS() uint64 // Reads number of objects saved in write-cache. It is called on write-cache initialization step. Read() error // Flushes the values and closes the storage. It is called on write-cache shutdown. FlushAndClose() }
ObjectCounters is an interface of the storage of cached object amount.
type Option ¶
type Option func(*options)
Option represents write-cache configuration option.
func WithBlobstor ¶
WithBlobstor sets main object storage.
func WithFlushWorkersCount ¶
func WithMaxBatchDelay ¶ added in v0.29.0
WithMaxBatchDelay sets max batch delay for the small object database.
func WithMaxBatchSize ¶ added in v0.29.0
WithMaxBatchSize sets max batch size for the small object database.
func WithMaxCacheSize ¶ added in v0.25.0
WithMaxCacheSize sets maximum write-cache size in bytes.
func WithMaxMemSize ¶
WithMaxMemSize sets maximum size for in-memory DB.
func WithMaxObjectSize ¶
WithMaxObjectSize sets maximum object size to be stored in write-cache.
func WithObjectCounters ¶ added in v0.25.0
func WithObjectCounters(v ObjectCounters) Option
WithObjectCounters sets ObjectCounters instance needed for cache write-cache size estimation.
func WithSmallObjectSize ¶
WithSmallObjectSize sets maximum object size to be stored in write-cache.