update datanode design docs (#5939)

Signed-off-by: Nyangxuan <xuan.yang@zilliz.com>

docs/design_docs/datanode_flowgraph_recovery_design_0604_2021.md

 # DataNode Flowgraph Recovery Design
 
 update: 6.4.2021, by [Goose](https://github.com/XuanYang-cn)
+update: 6.21.2021, by [Goose](https://github.com/XuanYang-cn)
 
 ## 1. Common Sense
 A. 1 message stream to 1 vchannel, so there are 1 start position and 1 end position in 1 message pack
@@ -11,7 +12,11 @@ An optimization: update position of
 C. DataNode auto-flush is a valid flush.
 D. DDL messages are now in DML Vchannels.
 
-## 2. Flowgraph Recovery
+## 2. Segments in Flowgraph
+
+![segments](graphs/segments.png)
+
+## 3. Flowgraph Recovery
 ### A. Save checkpoints
 When a flowgraph flushes a segment, we need to save these things:
 - current segment's binlog paths,
@@ -27,7 +32,21 @@ Whether save successfully:
 ### B. Recovery from a set of checkpoints
 1. We need all positions of all segments in this vchannel `p1, p2, ... pn`
 
-    [TBD] A design of WatchDmChannelReq
+A design of WatchDmChannelReq
+``` proto
+message VchannelInfo {
+  int64 collectionID = 1;
+  string channelName = 2;
+  internal.MsgPosition seek_position = 3;
+  repeated SegmentInfo unflushedSegments = 4;
+  repeated int64 flushedSegments = 5;
+}
+
+message WatchDmChannelsRequest {
+  common.MsgBase base = 1;
+  repeated VchannelInfo vchannels = 2;
+}
+```
 
 2. We want to filter msgPacks based on these positions.
 

docs/design_docs/datanode_recovery_design_0513_2021.md

@@ -2,6 +2,7 @@
 
 update: 5.21.2021, by [Goose](https://github.com/XuanYang-cn)  
 update: 6.03.2021, by [Goose](https://github.com/XuanYang-cn)
+update: 6.21.2021, by [Goose](https://github.com/XuanYang-cn)
 
 ## What's DataNode?
 
@@ -41,7 +42,7 @@ Vchannel is stateful because we don't want to process twice what's already proce
 already persistant. In DataNode's terminology, a message is processed if it's been flushed.
 
 DataService tells DataNode stateful vchannel infos through RPC `WatchDmChannels`, so that DataNode won't process
-the same messages over and over again. So flowgraph needs ability to comsume messages in the middle of a vchannel.
+the same messages over and over again. So flowgraph needs ability to consume messages in the middle of a vchannel.
 
 DataNode tells DataService vchannel states after each flush through RPC `SaveBinlogPaths`, so that DataService
 keep the vchannel states update.
@@ -51,7 +52,7 @@ keep the vchannel states update.
 
 ### 1. DataNode no longer interacts with Etcd except service registering
 
-#### **O1-1** DataService rather than DataNode saves binlog paths into Etcd
+#### DataService rather than DataNode saves binlog paths into Etcd
     
    ![datanode_design](graphs/datanode_design_01.jpg)
 
@@ -65,36 +66,23 @@ message ID2PathList {
     repeated string Paths = 2;
 }
 
+message CheckPoint {
+    int64 segmentID = 1;
+    internal.MsgPosition position = 2;
+    int64 num_of_rows = 3;
+}
+
 message SaveBinlogPathsRequest {
     common.MsgBase base = 1;
     int64 segmentID = 2;
     int64 collectionID = 3;
-    ID2PathList field2BinlogPaths = 4;
-    ID2PathList coll2TsBinlogPaths = 5;
-    ID2PathList coll2DdlBinlogPaths = 6;
-    repeated internal.MsgPosition start_positions = 7;
-    repeated internal.MsgPosition end_positions = 8;
+    repeated ID2PathList field2BinlogPaths = 4;
+    repeated CheckPoint checkPoints = 7;
+    repeated SegmentStartPosition start_positions = 6;
+    bool flushed = 7;
  }
 ```
 
-##### DataService Etcd Binlog Meta Design
-
-The same as DataNode
-
-```proto
-// key: ${prefix}/${segmentID}/${fieldID}/${idx}
-message SegmentFieldBinlogMeta {
-    int64  fieldID = 1;
-    string binlog_path = 2;
-}
-
-// key: ${prefix}/${collectionID}/${idx}
-message DDLBinlogMeta {
-    string ddl_binlog_path = 1;
-    string ts_binlog_path = 2;
-}
-```
-    
 ### 4. DataNode with collection with flowgraph with vchannel designs
 
 #### The winner
@@ -107,22 +95,17 @@ message DDLBinlogMeta {
 Change `WatchDmChannelsRequest` proto.
 
 ``` proto
-message PositionPair {
-  internal.MsgPosition start_position = 1;
-  internal.MsgPosition end_position = 2;
-}
-
-message VchannelPair {
+message VchannelInfo {
   int64 collectionID = 1;
-  string dml_vchannel_name = 2;
-  string ddl_vchannel_name = 3;
-  PositionPair ddl_position = 4;
-  PositionPair dml_position = 5;
+  string channelName = 2;
+  internal.MsgPosition seek_position = 3;
+  repeated SegmentInfo unflushedSegments = 4;
+  repeated int64 flushedSegments = 5;
 }
 
 message WatchDmChannelsRequest {
   common.MsgBase base = 1;
-  repeated VchannelPair vchannels = 2;
+  repeated VchannelInfo vchannels = 2;
 }
 ```
 
@@ -134,8 +117,9 @@ type DataNode struct {
     ...
     vchan2Sync map[string]*dataSyncService
     vchan2FlushCh map[string]chan<- *flushMsg
+
+    clearSignal chan UniqueID
     ...
-    replica Replica // TODO remove
 }
 
 // DataSyncService
@@ -147,7 +131,6 @@ type dataSyncService struct {
 	idAllocator  allocatorInterface
 	msFactory    msgstream.Factory
 	collectionID UniqueID
-	segmentIDs   []UniqueID // getSegmentIDs() of Replica
 }
 ```
 
@@ -155,24 +138,12 @@ DataNode Init -> Resigter to Etcd -> Discovery data service -> Discover master s
 
 WatchDmChannels -> new dataSyncService -> HEALTH
 
-```proto
-message WatchDmChannelsRequest {
-  common.MsgBase base = 1;
-  repeated VchannelPair vchannels = 2;
-}
-```
 `WatchDmChannels:`
 
 1. If `DataNode.vchan2Sync` is empty, DataNode is in IDLE, `WatchDmChannels` will create new dataSyncService for every unique vchannel, then DataNode is in HEALTH.
 2. If vchannel name of `VchannelPair` is not in `DataNode.vchan2Sync`, create a new dataSyncService.
 3. If vchannel name of `VchannelPair` is in `DataNode.vchan2Sync`, ignore.
 
-`newDataSyncService:`
-
-```go
-func newDataSyncService(ctx context.Context, flushChan <-chan *flushMsg, replica Replica,
-    alloc allocatorInterface, factory msgstream.Factory, vchanPair *datapb.VchannelPair) *dataSyncService
-
 ```
 
 #### The boring design

docs/developer_guides/chap09_data_service.md

@@ -286,7 +286,7 @@ type DataNode interface {
 ```go
 type WatchDmChannelRequest struct {
 	Base         *commonpb.MsgBase
-	ChannelNames []string
+	Vchannels    []*VchannelInfo
 }
 ```
 
@@ -326,5 +326,17 @@ type SegmentStatisticsMsg struct {
 	BaseMsg
 	SegmentStatistics
 }
+
+```
+#### 8.3 DataNode Time Tick Channel
+
+* *DataNode Tt Msg*
+
+```go
+message DataNodeTtMsg {
+    Base        *commonpb.MsgBase
+    ChannelName string
+    Timestamp   uint64
+}
 ```