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docs/scratch.md

+```plantuml
+    @startuml create_table
+    skinparam sequenceMessageAlign center
+    skinparam responseMessageBelowArrow true
+
+    participant APP as app
+    box "dnode1"
+        participant RPC as rpc
+        participant VNODE as vnode
+        participant SYNC as sync
+    end box
+
+    box "dnode2"
+        participant SYNC as sync2
+        participant VNODE as vnode2
+    end box
+
+    box "dnode3"
+        participant SYNC as sync3
+        participant VNODE as vnode3
+    end box
+
+    ' APP send request to dnode and RPC in dnode recv the request
+    app ->rpc: create table req
+
+    ' RPC call vnodeProcessReq() function to process the request
+    rpc -> vnode: vnodeProcessReq
+    note right
+    callback function 
+    run in RPC module 
+    threads. The function
+    only puts the request
+    to a vnode queue.
+    end note
+
+    ' VNODE call vnodeProcessReqs() function to integrate requests and process as a whole
+    vnode -> vnode: vnodeProcessReqs()
+    note right
+    integrate reqs and 
+    process as a whole
+    end note
+
+
+    ' sync the request to other nodes
+    vnode -> sync: syncProcessReqs()
+
+    ' make request persistent
+    ' sync -->vnode: walWrite()\n(callback function)
+
+    ' replicate requests to other DNODES
+    sync -> sync2: replication req
+    sync -> sync3: replication req
+    sync2 -> vnode2: walWrite()\n(callback function)
+    sync2 --> sync: replication rsp\n(confirm)
+    sync3 -> vnode3: walWrite()\n(callback function)
+
+    sync3 --> sync: replication rsp\n(confirm)
+
+    ' send apply request
+    sync -> sync2: apply req
+    sync -> sync3: apply req
+
+    ' vnode apply
+    sync2 -> vnode2: vnodeApplyReqs()
+    sync3 -> vnode3: vnodeApplyReqs()
+
+    ' call apply request
+    sync --> vnode: vnodeApplyReqs()\n(callback function)
+
+    ' send response
+    vnode --> rpc: rpcSendRsp()
+
+    ' dnode send response to APP
+    rpc --> app: create table rsp
+    @enduml
+```
+
+```plantuml
+    @startuml vnode_process_write
+    box "dnode1"
+        participant CRPC as crpc
+        participant VNODE as vnode
+        participant SYNC as sync
+    end box
+
+    -> crpc: create table/submit req
+
+    ' In CRPC threads
+    group #pink "In CRPC threads"
+        crpc -> vnode:vnodeProcessReq()
+        note right
+            A callback function
+            run by CRPC thread
+            to put the request
+            to a vnode queue
+        end note
+    end
+
+    ' In VNODE worker threads
+    group #lightblue "In VNODE worker threads"
+        vnode -> vnode: vnodeProcessReqs()
+        note right
+            VNODE process requests
+            accumulated in a 
+            vnode write queue and
+            process the batch reqs
+            as a whole
+        end note
+
+        vnode -> sync: syncProcessReqs()
+
+        sync -> : replication req1
+        sync -> : replication req2
+    end
+
+    group #red "SYNC threads"
+        sync <- : replication rsp1
+        sync <- : replication rsp2
+        sync -> vnode: notify apply
+    end
+
+    group #lightblue "In VNODE worker threads"
+        vnode -> vnode: vnodeApplyReqs()
+        vnode -> crpc:
+    end
+
+    <- crpc: create table/submit rsp
+
+    @enduml
+```
+
+```plantuml
+    @startuml replication_process
+    participant SYNC as sync
+    participant VNODE as vnode
+
+    group #pink "SYNC threads"
+        -> sync: replication req
+
+        sync -> sync: syncProcessReqs()
+        note right
+            In the replication
+            only data is
+            persisted and response
+            is sent back
+        end note
+
+        <- sync: replication rsp
+    end
+
+    @enduml
+```
+
+```plantuml
+    @startuml comfirm_process
+    participant SYNC as sync
+    participant VNODE as vnode
+
+    group #pink "SYNC threads"
+        -> sync: replication rsp
+
+        sync -> vnode: notify VNODE \nthread to process\n the reqs
+    end
+
+    group #lightblue "VNODE worker threads"
+        vnode -> vnode: vnodeApplyReqs()
+    end
+    @enduml
+```
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