milvus/docs/developer_guides/chap07_query_service.md

## 8. Query Service

#### 8.1 Overview

<img src="./figs/query_service.jpeg" width=700>



#### 8.2 Query Service Interface

```go
type QueryService interface {
  Service
  
  RegisterNode(req RegisterNodeRequest) (RegisterNodeResponse, error)
  
  ShowCollections(req ShowCollectionRequest) (ShowCollectionResponse, error)
  LoadCollection(req LoadCollectionRequest) error
  ReleaseCollection(req ReleaseCollectionRequest) error
  
  ShowPartitions(req ShowPartitionRequest) (ShowPartitionResponse, error)
  GetPartitionStates(req PartitionStatesRequest) (PartitionStatesResponse, error)
  LoadPartitions(req LoadPartitonRequest) error
  ReleasePartitions(req ReleasePartitionRequest) error
  
  CreateQueryChannel() (CreateQueryChannelResponse, error)
}
```



* *RequestBase*

```go
type RequestBase struct {
  MsgType MsgType
  ReqID	UniqueID
  Timestamp Timestamp
  RequestorID UniqueID
}
```

* *RegisterNode*

```go
type RegisterNodeRequest struct {
  RequestBase
  Address string
  Port int64
}

type RegisterNodeResponse struct {
  //InitParams
}
```

* *ShowCollections*

```go
type ShowCollectionRequest struct {
  RequestBase
  DbID UniqueID
}

type ShowCollectionResponse struct {
  CollectionIDs []UniqueID
}
```

* *LoadCollection*

```go
type LoadCollectionRequest struct {
  RequestBase
  DbID UniqueID
  CollectionID UniqueID
}
```

* *ReleaseCollection*

```go
type ReleaseCollectionRequest struct {
  RequestBase
  DbID UniqueID
  CollectionID UniqueID
}
```

* *ShowPartitions*

```go
type ShowPartitionRequest struct {
  RequestBase
  DbID UniqueID
  CollectionID UniqueID
}

type ShowPartitionResponse struct {
  PartitionIDs []UniqueID
}
```

* *GetPartitionStates*

```go
type PartitionState = int

const (
  NOT_EXIST PartitionState = 0
  NOT_PRESENT PartitionState = 1
  ON_DISK PartitionState = 2
  PARTIAL_IN_MEMORY PartitionState = 3
	IN_MEMORY PartitionState = 4
  PARTIAL_IN_GPU PartitionState = 5
  IN_GPU PartitionState = 6
)

type PartitionStatesRequest struct {
  RequestBase
  DbID UniqueID
  CollectionID UniqueID
  PartitionIDs []UniqueID
}

type PartitionStates struct {
  PartitionID UniqueID
  State PartitionState
}

type PartitionStatesResponse struct {
  States []PartitionStates
}
```

* *LoadPartitions*

```go
type LoadPartitonRequest struct {
  RequestBase
  DbID UniqueID
  CollectionID UniqueID
  PartitionIDs []UniqueID
}
```

* *ReleasePartitions*

```go
type ReleasePartitionRequest struct {
  RequestBase
  DbID UniqueID
  CollectionID UniqueID
  PartitionIDs []UniqueID
}
```

* *CreateQueryChannel*

```go
type CreateQueryChannelResponse struct {
  RequestChannelID string
  ResultChannelID string
}
```



#### 8.2 Query Node Interface

```go
type QueryNode interface {
  Service
  
  AddQueryChannel(req AddQueryChannelRequest) error
  RemoveQueryChannel(req RemoveQueryChannelRequest) error
  WatchDmChannels(req WatchDmChannelRequest) error
  //SetTimeTickChannel(channelID string) error
  //SetStatsChannel(channelID string) error
  
  LoadSegments(req LoadSegmentRequest) error
  ReleaseSegments(req ReleaseSegmentRequest) error
  //DescribeParition(req DescribeParitionRequest) (PartitionDescriptions, error)
}
```



* *AddQueryChannel*

```go
type AddQueryChannelRequest struct {
  RequestChannelID string
  ResultChannelID string
}
```

* *RemoveQueryChannel*

```go
type RemoveQueryChannelRequest struct {
  RequestChannelID string
  ResultChannelID string
}
```

* *WatchDmChannels*

```go
type WatchDmChannelRequest struct {
  InsertChannelIDs []string
}
```

* *LoadSegments*

```go
type LoadSegmentRequest struct {
  RequestBase
  DbID UniqueID
  CollectionID UniqueID
  PartitionID UniqueID
  SegmentIDs []UniqueID
  FieldIDs []int64
}
```

* *ReleaseSegments*

```go
type ReleaseSegmentRequest struct {
  RequestBase
  DbID UniqueID
  CollectionID UniqueID
  PartitionID UniqueID
  SegmentIDs []UniqueID
}
```



#### 8.2 Collection Replica

$collectionReplica$ contains a in-memory local copy of persistent collections. In common cases, the system has multiple query nodes. Data of a collection will be distributed across all the available query nodes, and each query node's $collectionReplica$ will maintain its own share (only part of the collection).
Every replica tracks a value called tSafe which is the maximum timestamp that the replica is up-to-date.

###### 8.1.1 Collection

``` go
type Collection struct {
  Name string
  Id uint64
  Fields map[string]FieldMeta
  SegmentsId []uint64
  
  cCollectionSchema C.CCollectionSchema
}
```



###### 8.1.2 Field Meta

```go
type FieldMeta struct {
  Name string
  Id uint64
  IsPrimaryKey bool
  TypeParams map[string]string
  IndexParams map[string]string
}
```



###### 8.1.3 Segment

``` go
type Segment struct {
  Id uint64
  ParitionName string
  CollectionId uint64
  OpenTime Timestamp
  CloseTime Timestamp
  NumRows uint64
  
  cSegment C.CSegmentBase
}
```



#### 8.3 Data Sync Service

```go
type dataSyncService struct {
	ctx context.Context
	pulsarURL string
	fg *flowgraph.TimeTickedFlowGraph
	msgStream *msgstream.PulsarMsgStream
	dataReplica Replica
}
```