diff --git a/docs/design_docs/graphs/dml_drop_collection.png b/docs/design_docs/graphs/dml_drop_collection.png new file mode 100644 index 0000000000..7b9d54a087 Binary files /dev/null and b/docs/design_docs/graphs/dml_drop_collection.png differ diff --git a/docs/design_docs/graphs/dml_release_collection.png b/docs/design_docs/graphs/dml_release_collection.png new file mode 100644 index 0000000000..501aea82ec Binary files /dev/null and b/docs/design_docs/graphs/dml_release_collection.png differ diff --git a/docs/design_docs/graphs/dml_release_flow_graph_on_data_node.png b/docs/design_docs/graphs/dml_release_flow_graph_on_data_node.png new file mode 100644 index 0000000000..9c9cd8ed83 Binary files /dev/null and b/docs/design_docs/graphs/dml_release_flow_graph_on_data_node.png differ diff --git a/docs/design_docs/milvus_drop_collection_en.md b/docs/design_docs/milvus_drop_collection_en.md new file mode 100644 index 0000000000..a2215e5dd9 --- /dev/null +++ b/docs/design_docs/milvus_drop_collection_en.md @@ -0,0 +1,189 @@ +# Drop Collection +`Milvus 2.0` use `Collection` to represent a set of data, like `Table` in traditional database. Users can create or drop `Collection`. Altering the `Schema` of `Collection` is not supported yet. This article introduces the execution path of `Drop Collection`, at the end of this article, you should know which components are involved in `Drop Collection`. + +The execution flow of `Drop Collection` is shown in the following figure: + +![drop_collection](./graphs/dml_drop_collection.png) + +1. Firstly, `SDK` starts a `DropCollection` request to `Proxy` via `Grpc`, the `proto` is defined as follows: +```proto +service MilvusService { + ... + + rpc DropCollection(DropCollectionRequest) returns (common.Status) {} + + ... +} + +message DropCollectionRequest { + common.MsgBase base = 1; // must + string db_name = 2; + string collection_name = 3; // must +} +``` + +2. When received the `DropCollection` request, the `Proxy` would wraps this request into `DropCollectionTask`, and pushs this task into `DdTaskQueue` queue. After that, `Proxy` would call method of `WatiToFinish` to wait until the task finished. +```go +type task interface { + TraceCtx() context.Context + ID() UniqueID // return ReqID + SetID(uid UniqueID) // set ReqID + Name() string + Type() commonpb.MsgType + BeginTs() Timestamp + EndTs() Timestamp + SetTs(ts Timestamp) + OnEnqueue() error + PreExecute(ctx context.Context) error + Execute(ctx context.Context) error + PostExecute(ctx context.Context) error + WaitToFinish() error + Notify(err error) +} + +type DropCollectionTask struct { + Condition + *milvuspb.DropCollectionRequest + ctx context.Context + rootCoord types.RootCoord + result *commonpb.Status + chMgr channelsMgr + chTicker channelsTimeTicker +} +``` + +3. There is a backgroud service in `Proxy`, this service would get the `DropCollectionTask` from `DdTaskQueue`, and executes it in three phases. + - `PreExecute`, do some static checking at this phase, such as check if `Collection Name` is legal etc. + - `Execute`, at thie phase, `Proxy` would send `DropCollection` request to `RootCoord` via `Grpc`,and wait the reponse, the `proto` is defined as follow: + ```proto + service RootCoord { + ... + + rpc DropCollection(milvus.DropCollectionRequest) returns (common.Status) {} + + ... + } + ``` + - `PostExecute`, `Proxy` would delete the `Collection`'s meta from global meta table at this phase. + +4. `RootCoord` would wraps the `DropCollection` request into `DropCollectionReqTask`, and then call function `executeTask`. `executeTask` would return until the `context` is done or `DropCollectionReqTask.Execute` returned. +```go +type reqTask interface { + Ctx() context.Context + Type() commonpb.MsgType + Execute(ctx context.Context) error + Core() *Core +} + +type DropCollectionReqTask struct { + baseReqTask + Req *milvuspb.DropCollectionRequest +} +``` + +5. Firstly, `RootCoord` would delete `Collection`'s meta from `metaTable`, including `schema`,`partition`, `segment`,`index`, all of these delete operations are committed in one transaction. + +6. After `Collection`'s meta has been deleted from `metaTable`, `Milvus` would consider this collection has been deleted successfully. + +7. `RootCoord` would alloc a timestamp from `TSO` before deleting `Collection`'s meta from `metaTable`, and this timestamp is considered as the point when the collection was deleted. + +8. `RoooCoord` would send a message of `DropCollectionRequest` into `MsgStream`, and other components, who has subscribe to the `MsgStream`, would be notified. The `Proto` of `DropCollectionRequest` is defined as follow: +```proto +message DropCollectionRequest { + common.MsgBase base = 1; + string db_name = 2; + string collectionName = 3; + int64 dbID = 4; + int64 collectionID = 5; +} + +``` + +9. After these operations, `RootCoord` would update internal timestamp. + +10. Then `RootCoord` would start a `ReleaseCollection` request to `QueryCoord` via `Grpc` , notify `QueryCoord` to release all the resouces that related to this `Collection`. This `Grpc` request is done in another `goroutine`, so it would not block the main thread. The `proto` is defined as follow: +```proto +service QueryCoord { + ... + + rpc ReleaseCollection(ReleaseCollectionRequest) returns (common.Status) {} + + ... +} + +message ReleaseCollectionRequest { + common.MsgBase base = 1; + int64 dbID = 2; + int64 collectionID = 3; + int64 nodeID = 4; +} +``` + +11. At last, `RootCoord` would send `InvalidateCollectionMetaCache` request to each `Proxy`, notify `Proxy` to remove `Collection`'s meta, the `proto` is defined as follow: +```proto +service Proxy { + ... + + rpc InvalidateCollectionMetaCache(InvalidateCollMetaCacheRequest) returns (common.Status) {} + + ... +} + +message InvalidateCollMetaCacheRequest { + common.MsgBase base = 1; + string db_name = 2; + string collection_name = 3; +} +``` + +12. The execution flow of `QueryCoord.ReleaseCollection` is shown in the follwing figure. + +![releae_collection](./graphs/dml_release_collection.png) + +13. `QueryCoord` would wraps `ReleaseCollection` into `ReleaseCollectionTask`, and push the task into `TaskScheduler` + +14. There is a backgroud service in `QueryCoord`, this service would get the `ReleaseCollectionTask` from `TaskScheduler`, and executes it in three phases. + - `PreExecute`, `ReleaseCollectionTask` would only print debug log at this phase. + - `Execute`, there are two jobs at this phase: + - send a `ReleaseDQLMessageStream` request to `RootCoord` via `Grpc`, `RootCoord` would redirect the `ReleaseDQLMessageStream` request to each `Proxy`, notify the `Proxy` that not processing any message of this `Collection` anymore. The `proto` is defined as follow: + ```proto + message ReleaseDQLMessageStreamRequest { + common.MsgBase base = 1; + int64 dbID = 2; + int64 collectionID = 3; + } + ``` + - send a `ReleaseCollection` request to each `QueryNode` via `Grpc`, notify the `QueryNode` to release all the resources related to this `Collection`, including `Index`, `Segment`, `FlowGraph`, etc. `QueryNode` would no longer read any message from this `Collection`'s `MsgStream` anymore + ```proto + service QueryNode { + ... + + rpc ReleaseCollection(ReleaseCollectionRequest) returns (common.Status) {} + + ... + } + + message ReleaseCollectionRequest { + common.MsgBase base = 1; + int64 dbID = 2; + int64 collectionID = 3; + int64 nodeID = 4; + } + ``` + - `PostExecute`, `ReleaseCollectionTask` would only print debug log at this phase. + +15. After these operations, `QueryCoord` would send `ReleaseCollection`'s reponse to `RootCoord + +16. At `Step 8`, `RoooCoord` has sent a message of `DropCollectionRequest` into `MsgStream`, `DataNode` would subscribe this `MsgStream`, so `DataNode` would be notified to released the resources. The execution flow is shown in the following figure. + +![releae_collection](./graphs/dml_release_flow_graph_on_data_node.png) + +17. In `DataNode`, each `MsgStream` will have a `FlowGraph`, all the messages are processed by that `FlowGraph`. When the `DataNode` receives the message of `DropCollectionRequest`, `DataNode` would notify `BackouGroundGC`, which is a background service on `DataNode`, to release the resouces. + +*Notes*: +1. Currently, the `DataCoord` has not response to the `DropCollection`, so the `Collection`'s `segment meta` are still exist in the `DataCoord`'s `metaTable`, and the `Binlog` files belongs to this `Collection` are still exist on the persistent storage. +2. Currently, the `IndexCoord` has not response to the `DropCollection`, so the `Collection`'s `index file` are still exist on the persistent storage. + + + +