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mariadb-columnstore-engine/docs/mcssystemready_and_SessionManagerServer_flags.md

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- SessionManagerServer has a number of state flags:
- SS_READY = 1; // Set by dmlProc one time when dmlProc is ready
- SS_SUSPENDED = 2// Set by console when the system has been suspended by user.
- SS_SUSPEND_PENDING = 4// Set by console when user wants to suspend, but writing is occuring.
- SS_SHUTDOWN_PENDING = 8 // Set by console when user wants to shutdown, but writing is occuring.
- SS_ROLLBACK = 16; // In combination with a PENDING flag, force a rollback as soon as possible.
- SS_FORCE = 32; // In combination with a PENDING flag, force a shutdown without rollback.
- SS_QUERY_READY = 64 // Set by PrimProc after ExeMgr thread is up and running
- The actual state is a combination of flags.
- The state of a running cluster resides in SessionManagerServer instance attribute that is inside a controllernode process.
- There is a cold storage for a state that is stored in a file pointed by SessionManager.TxnIDFile with /var/lib/columnstore/data1/systemFiles/dbrm/SMTxnID. This cold state is loaded up when controllernode starts.
- The following FSM diagram demostrates some transitions. !It is not full yet!
```mermaid
stateDiagram-v2
ZeroState --> InitState : Controllernode reads cold state
InitState --> InitState_6 : ExeMgr threads starts in PP/SS_QUERY_READY
InitState_6 --> InitState_6_!1 : DMLProc begins rollbackAll / !SS_READY
InitState_6_!1 --> InitState_6_!1 : DMLProc fails rollbackAll /
InitState_6_!1 --> InitState_6_1 : DMLProc finishes rollbackAll sucessfully / SS_READY
InitState_6_1 --> InitState_16_8_6_1 : cmapi_gets_shutdown
InitState_16_8_6_1 --> ZeroState : see rollback_is_ok
InitState_16_8_6_1 --> InitState_32_16_8_6_1 : see failed_rollback
InitState_32_16_8_6_1 --> ZeroState : force DMLProc shutdown
```
cmapi_gets_shutdown: CMAPI gets shutdown request with TO / SS_SHUTDOWN_PENDING + SS_ROLLBACK
rollback_is_ok: DMLProc sucessfully rollbacks active txns within TO and cluster stops
failed_rollback: DMLProc sucessfully rollbacks active txns within TO and cluster stops