7.2 KiB
Appendix A. Basic Components
A.1 Watchdog
type ActiveComponent interface {
Id() string
Status() Status
Clean() Status
Restart() Status
}
type ComponentHeartbeat interface {
Id() string
Status() Status
Serialize() string
}
type Watchdog struct {
targets [] *ActiveComponent
heartbeats ComponentHeartbeat chan
}
// register ActiveComponent
func (dog *Watchdog) Register(target *ActiveComponent)
// called by ActiveComponents
func (dog *Watchdog) PutHeartbeat(heartbeat *ComponentHeartbeat)
// dump heatbeats as log stream
func (dog *Watchdog) dumpHeartbeat(heartbeat *ComponentHeartbeat)
A.2 Global Parameter Table
type GlobalParamsTable struct {
params memoryKV
}
func (gparams *GlobalParamsTable) Save(key, value string) error
func (gparams *GlobalParamsTable) Load(key string) (string, error)
func (gparams *GlobalParamsTable) LoadRange(key, endKey string, limit int) ([]string, []string, error)
func (gparams *GlobalParamsTable) Remove(key string) error
func (gparams *GlobalParamsTable) LoadYaml(filePath string) error
- LoadYaml(filePath string) turns a YAML file into multiple key-value pairs. For example, given the following YAML
etcd:
address: localhost
port: 12379
rootpath: milvus/etcd
GlobalParamsTable.LoadYaml will insert three key-value pairs into params
"etcd.address" -> "localhost"
"etcd.port" -> "12379"
"etcd.rootpath" -> "milvus/etcd"
A.4 Time Ticked Flow Graph
A.4.1 Flow Graph States
type flowGraphStates struct {
startTick Timestamp
numActiveTasks map[string]int32
numCompletedTasks map[string]int64
}
A.4.2 Message
type Msg interface {
TimeTick() Timestamp
SkipThisTick() bool
DownStreamNodeIdx() int32
}
type SkipTickMsg struct {}
func (msg *SkipTickMsg) SkipThisTick() bool // always return true
A.4.3 Node
type Node interface {
Name() string
MaxQueueLength() int32
MaxParallelism() int32
SetPipelineStates(states *flowGraphStates)
Operate([]*Msg) []*Msg
}
type baseNode struct {
Name string
maxQueueLength int32
maxParallelism int32
graphStates *flowGraphStates
}
func (node *baseNode) MaxQueueLength() int32
func (node *baseNode) MaxParallelism() int32
func (node *baseNode) SetMaxQueueLength(n int32)
func (node *baseNode) SetMaxParallelism(n int32)
func (node *baseNode) SetPipelineStates(states *flowGraphStates)
A.4.4 Flow Graph
type nodeCtx struct {
node *Node
inputChans [](*chan *Msg)
outputChans [](*chan *Msg)
inputMsgs [](*Msg List)
downstreams []*nodeCtx
skippedTick Timestamp
}
func (nodeCtx *nodeCtx) Start(ctx context.Context) error
Start() will enter a loop. In each iteration, it tries to collect input messges from inputChan, then prepare node's input. When input is ready, it will trigger node.Operate. When node.Operate returns, it sends the returned Msg to outputChans, which connects to the downstreams' inputChans.
type TimeTickedFlowGraph struct {
states *flowGraphStates
nodeCtx map[string]*nodeCtx
}
func (*pipeline TimeTickedFlowGraph) AddNode(node *Node)
func (*pipeline TimeTickedFlowGraph) SetEdges(nodeName string, in []string, out []string)
func (*pipeline TimeTickedFlowGraph) Start() error
func (*pipeline TimeTickedFlowGraph) Close() error
func NewTimeTickedFlowGraph(ctx context.Context) *TimeTickedFlowGraph
A.5 ID Allocator
type IdAllocator struct {
}
func (allocator *IdAllocator) Start() error
func (allocator *IdAllocator) Close() error
func (allocator *IdAllocator) Alloc(count uint32) ([]int64, error)
func NewIdAllocator(ctx context.Context) *IdAllocator
A.6 Timestamp Allocator
A.6.1 Timestamp
Let's take a brief review of Hybrid Logical Clock (HLC). HLC uses 64bits timestamps which are composed of a 46-bits physical component (thought of as and always close to local wall time) and a 18-bits logical component (used to distinguish between events with the same physical component).
HLC's logical part is advanced on each request. The phsical part can be increased in two cases:
A. when the local wall time is greater than HLC's physical part,
B. or the logical part overflows.
In either cases, the physical part will be updated, and the logical part will be set to 0.
Keep the physical part close to local wall time may face non-monotonic problems such as updates to POSIX time that could turn time backward. HLC avoids such problems, since if 'local wall time < HLC's physical part' holds, only case B is satisfied, thus montonicity is guaranteed.
Milvus does not support transaction, but it should gurantee the deterministic execution of the multi-way WAL. The timestamp attached to each request should
- have its physical part close to wall time (has an acceptable bounded error, a.k.a. uncertainty interval in transaction senarios),
- and be globally unique.
HLC leverages on physical clocks at nodes that are synchronized using the NTP. NTP usually maintain time to within tens of milliseconds over local networks in datacenter. Asymmetric routes and network congestion occasionally cause errors of hundreds of milliseconds. Both the normal time error and the spike are acceptable for Milvus use cases.
The interface of Timestamp is as follows.
type timestamp struct {
physical uint64 // 18-63 bits
logical uint64 // 0-17 bits
}
type Timestamp uint64
A.6.2 Timestamp Oracle
type timestampOracle struct {
client *etcd.Client // client of a reliable meta service, i.e. etcd client
rootPath string // this timestampOracle's working root path on the reliable kv service
saveInterval uint64
lastSavedTime uint64
tso Timestamp // monotonically increasing timestamp
}
func (tso *timestampOracle) GetTimestamp(count uint32) ([]Timestamp, error)
func (tso *timestampOracle) saveTimestamp() error
func (tso *timestampOracle) loadTimestamp() error
A.6.3 Timestamp Allocator
type TimestampAllocator struct {}
func (allocator *TimestampAllocator) Start() error
func (allocator *TimestampAllocator) Close() error
func (allocator *TimestampAllocator) Alloc(count uint32) ([]Timestamp, error)
func NewTimestampAllocator() *TimestampAllocator
-
Batch Allocation of Timestamps
-
Expiration of Timestamps
A.7 KV
A.7.1 KV Base
type KVBase interface {
Load(key string) (string, error)
MultiLoad(keys []string) ([]string, error)
Save(key, value string) error
MultiSave(kvs map[string]string) error
Remove(key string) error
MultiRemove(keys []string) error
MultiSaveAndRemove(saves map[string]string, removals []string) error
Watch(key string) clientv3.WatchChan
WatchWithPrefix(key string) clientv3.WatchChan
LoadWithPrefix(key string) ( []string, []string, error)
}
- MultiLoad(keys []string) Load multiple kv pairs. Loads are done transactional.
- MultiSave(kvs map[string]string) Save multiple kv pairs. Saves are done transactional.
- MultiRemove(keys []string) Remove multiple kv pairs. Removals are done transactional.
A.7.2 Etcd KV
type EtcdKV struct {
client *clientv3.Client
rootPath string
}
func NewEtcdKV(etcdAddr string, rootPath string) *EtcdKV
EtcdKV implements all KVBase interfaces.