Bolt Protocol Server State Specification - Version 4

Version 4.0

Deltas

Compared to version 3 the RUN, PULL and DISCARD now can re-enter STREAMING or TX_STREAMING.

The server state transitions are using the updated set of messages defined in Bolt Protocol Message Specification Version 4.0.

Server States

Each connection maintained by a Bolt server will occupy one of several states throughout its lifetime.

This state is used to determine what actions may be undertaken by the client.

State Logic State Description
DISCONNECTED x no socket connection
CONNECTED x protocol handshake has been completed successfully
DEFUNCT x the socket connection has been permanently closed
READY   ready to accept a RUN message
STREAMING   Auto-commit Transaction, a result is available for streaming from the server
TX_READY   Explicit Transaction, ready to accept a RUN message
TX_STREAMING   Explicit Transaction, a result is available for streaming from the server
FAILED   a connection is in a temporarily unusable state
INTERRUPTED    

Server State - DISCONNECTED

No socket connection has yet been established. This is the initial state and exists only in a logical sense prior to the socket being opened.

Transitions from DISCONNECTED

Server State - CONNECTED

After a new protocol connection has been established and handshake has been completed successfully, the server enters the CONNECTED state. The connection has not yet been authenticated and permits only one transition, through successful initialization, into the READY state.

Transitions from CONNECTED

Server State - DEFUNCT

This is not strictly a connection state, but is instead a logical state that exists after a connection has been closed.

When DEFUNCT, a connection is permanently not usable.

This may arise due to a graceful shutdown or can occur after an unrecoverable error or protocol violation.

Clients and servers should clear up any resources associated with a connection on entering this state, including closing any open sockets.

This is a terminal state on which no further transitions may be carried out.

The <DISCONNECT> signal will set the connection in the DEFUNCT server state.

Server State - READY

Transitions from READY

Server State - STREAMING

When STREAMING, a result is available for streaming from server to client.

This result must be fully consumed or discarded by a client before the server can re-enter the READY state and allow any further queries to be executed.

Transitions from STREAMING

Request Message - DISCARD - State Transitions

State New State Response
STREAMING READY SUCCESS {"has_more": false}
STREAMING FAILED FAILURE {}
STREAMING STREAMING SUCCESS {"has_more": true}

Request Message - PULL - State Transitions

State New State Response
STREAMING READY [RECORD …] SUCCESS {"has_more": false}
STREAMING FAILED [RECORD …] FAILURE {}
STREAMING STREAMING [RECORD …] SUCCESS {"has_more": true}

Server State - TX_READY

Transitions from TX_READY

RUN Message State Transitions

State New State Response
TX_READY TX_STREAMING SUCCESS {"qid": id::Integer}
TX_READY FAILED FAILURE {}

Server State - TX_STREAMING

When TX_STREAMING, a result is available for streaming from server to client.

This result must be fully consumed or discarded by a client before the server can transition to the TX_READY state.

Transitions from TX_STREAMING

Request Message - RUN - State Transitions

State New State Response
TX_STREAMING TX_STREAMING SUCCESS {"qid": id::Integer}
TX_STREAMING FAILED FAILURE {}

Request Message - DISCARD - State Transitions

State New State Response
TX_STREAMING TX_READY or TX_STREAMING if there is other streams open SUCCESS {"has_more": false}
TX_STREAMING FAILED FAILURE {}
TX_STREAMING TX_STREAMING SUCCESS {"has_more": true}

Request Message - PULL - State Transitions

TX_READY or TX_STREAMING if there is other streams open

State New State Response
TX_STREAMING TX_READY or TX_STREAMING if there is other streams open [RECORD …] SUCCESS {"has_more": false}
TX_STREAMING FAILED [RECORD …] FAILURE {}
TX_STREAMING TX_STREAMING [RECORD …] SUCCESS {"has_more": true}

Server State - FAILED

When FAILED, a connection is in a temporarily unusable state.

This is generally as the result of encountering a recoverable error.

This mode ensures that only one failure can exist at a time, preventing cascading issues from batches of work.

Transitions from FAILED

Server State - INTERRUPTED

This state occurs between the server receiving the jump-ahead <INTERRUPT> and the queued RESET message, (the RESET message triggers an <INTERRUPT>).

Most incoming messages are ignored when the server are in an INTERRUPTED state, with the exception of the RESET that allows transition back to READY.

The <INTERRUPT> signal will set the connection in the INTERRUPTED server state.

Transitions from INTERRUPTED

Version 4.1

Deltas

No changes compared to version 4.0.

Version 4.2

Deltas

No changes compared to version 4.1.

Appendix - Bolt Message State Transitions

State Request Message Triggers Signal Server Response Summary Message New State
CONNECTED HELLO   SUCCESS {} READY
CONNECTED HELLO   FAILURE {} DEFUNCT
         
READY RUN   SUCCESS {} STREAMING
READY RUN   FAILURE {} FAILED
READY BEGIN   SUCCESS {} TX_READY
READY BEGIN   FAILURE {} FAILED
READY RESET <INTERRUPT> n/a  
READY GOODBYE <DISCONNECT> n/a DEFUNCT
         
STREAMING PULL   SUCCESS {"has_more": true} STREAMING
STREAMING PULL   SUCCESS {"has_more": false} READY
STREAMING PULL   FAILURE {} FAILED
STREAMING DISCARD   SUCCESS {"has_more": true} STREAMING
STREAMING DISCARD   SUCCESS {"has_more": false} READY
STREAMING DISCARD   FAILURE {} FAILED
STREAMING RESET <INTERRUPT> n/a  
STREAMING GOODBYE <DISCONNECT> n/a DEFUNCT
         
TX_READY RUN   SUCCESS {"qid": id::Integer} TX_STREAMING
TX_READY RUN   FAILURE {} FAILED
TX_READY COMMIT   SUCCESS {} READY
TX_READY COMMIT   FAILURE {} FAILED
TX_READY ROLLBACK   SUCCESS {} READY
TX_READY ROLLBACK   FAILURE {} FAILED
TX_READY RESET <INTERRUPT> n/a  
TX_READY GOODBYE <DISCONNECT> n/a DEFUNCT
         
TX_STREAMING RUN   SUCCESS {"qid": id::Integer} TX_STREAMING
TX_STREAMING RUN   FAILURE {} FAILED
TX_STREAMING PULL   SUCCESS {"has_more": true} TX_STREAMING
TX_STREAMING PULL   SUCCESS {"has_more": false} TX_READY or TX_STREAMING if there is other streams open
TX_STREAMING PULL   FAILURE {} FAILED
TX_STREAMING DISCARD   SUCCESS {"has_more": true} TX_STREAMING
TX_STREAMING DISCARD   SUCCESS {"has_more": false} TX_READY or TX_STREAMING if there is other streams open
TX_STREAMING DISCARD   FAILURE {} FAILED
TX_STREAMING RESET <INTERRUPT> n/a  
TX_STREAMING GOODBYE <DISCONNECT> n/a DEFUNCT
         
FAILED RUN   IGNORED FAILED
FAILED PULL   IGNORED FAILED
FAILED DISCARD   IGNORED FAILED
FAILED RESET <INTERRUPT> n/a  
FAILED GOODBYE <DISCONNECT> n/a DEFUNCT
         
INTERRUPTED RUN   IGNORED INTERRUPTED
INTERRUPTED PULL   IGNORED INTERRUPTED
INTERRUPTED DISCARD   IGNORED INTERRUPTED
INTERRUPTED BEGIN   IGNORED INTERRUPTED
INTERRUPTED COMMIT   IGNORED INTERRUPTED
INTERRUPTED ROLLBACK   IGNORED INTERRUPTED
INTERRUPTED RESET <INTERRUPT> SUCCESS {} READY
INTERRUPTED RESET <INTERRUPT> FAILURE {} DEFUNCT
INTERRUPTED GOODBYE <DISCONNECT> n/a DEFUNCT

The <INTERRUPT> signal,

State Signal Server Response Summary Message New State
READY <INTERRUPT> n/a INTERRUPTED
STREAMING <INTERRUPT> n/a INTERRUPTED
TX_READY <INTERRUPT> n/a INTERRUPTED
TX_STREAMING <INTERRUPT> n/a INTERRUPTED
FAILED <INTERRUPT> n/a INTERRUPTED
INTERRUPTED <INTERRUPT> n/a INTERRUPTED