Struct Ring

ring/ring.go:240–305

Ring is a Service that maintains an in-memory copy of a ring and watches for changes. Support for read-only instances requires use of ShuffleShard or ShuffleShardWithLookback prior to getting a ReplicationSet.

// Ring is a Service that maintains an in-memory copy of a ring and watches for changes.
// Support for read-only instances requires use of ShuffleShard or ShuffleShardWithLookback prior to getting a ReplicationSet.
type Ring struct {
	services.Service

	key      string
	cfg      Config
	KVClient kv.Client
	strategy ReplicationStrategy

	mtx              sync.RWMutex
	ringDesc         *Desc
	ringTokens       []uint32
	ringTokensByZone map[string][]uint32

	// Oldest value of RegisteredTimestamp from all instances. If any instance had RegisteredTimestamp == 0,
	// then this value will be 0.
	oldestRegisteredTimestamp int64

	readOnlyInstances *int // Number of instances with ReadOnly flag set. Only valid if not nil.
	// Oldest value of ReadOnlyUpdatedTimestamp for read-only instances. If there are no read-only instances,
	// or if any read-only instance has ReadOnlyUpdatedTimestamp == 0 (which should not happen), then this value will be 0.
	// Only valid if not nil.
	oldestReadOnlyUpdatedTimestamp *int64

	// Maps a token with the information of the instance holding it. This map is immutable and
	// cannot be changed in place because it's shared "as is" between subrings (the only way to
	// change it is to create a new one and replace it).
	ringInstanceByToken map[uint32]instanceInfo

	// When did a set of instances change the last time (instance changing state or heartbeat is ignored for this timestamp).
	lastTopologyChange time.Time

	// List of zones for which there's at least 1 instance in the ring. This list is guaranteed
	// to be sorted alphabetically.
	ringZones []string

	// Map containing all ring zones ever discovered, even if they have no instances,
	// capped at 32 zones to limit cardinality.
	trackedRingZones map[string]struct{}

	// Number of registered instances with tokens.
	instancesWithTokensCount int

	// Number of registered instances per zone.
	instancesCountPerZone map[string]int

	// Number of registered instances with tokens per zone.
	instancesWithTokensCountPerZone map[string]int

	// Number of registered instances are writable and have tokens.
	writableInstancesWithTokensCount int

	// Number of registered instances with tokens per zone that are writable.
	writableInstancesWithTokensCountPerZone map[string]int

	// Cache of shuffle-sharded subrings per identifier. Invalidated when topology changes.
	// If set to nil, no caching is done (used by tests, and subrings).
	shuffledSubringCache             map[subringCacheKey]*Ring
	shuffledSubringWithLookbackCache map[subringCacheKey]cachedSubringWithLookback[*Ring]