From 188c858a12705164b7ae5f1ad418821bedd94bb4 Mon Sep 17 00:00:00 2001 From: Andrew Chen Date: Mon, 29 Jun 2020 15:59:59 +0000 Subject: SERVER-48754 Adding Internal Ingress Networking README --- src/mongo/transport/README.md | 42 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 42 insertions(+) create mode 100644 src/mongo/transport/README.md (limited to 'src/mongo/transport') diff --git a/src/mongo/transport/README.md b/src/mongo/transport/README.md new file mode 100644 index 00000000000..ca9158e37dc --- /dev/null +++ b/src/mongo/transport/README.md @@ -0,0 +1,42 @@ +# Internal Ingress Networking +Ingress networking refers to when a MongoDB process receives incoming requests from a client. + +When a client wants to interact with a server, they must first establish a connection. The server listens on a single port for incoming client connections. Once a client connection is received over an ephermeral port, a client session is created out of this connection and commands begin to be processed on a new dedicated thread. + +The session takes in commands received from the client and hands them off to a [ServiceEntryPointImpl]. This entry point will spawn threads to perform specific tasks via a [ServiceExecutor], which is then used to initialize a [ServiceStateMachine]. The ServiceStateMachine is a state machine that manages the life cycle of the client connection. + +These are the valid state transitions: +* *Source -> SourceWait -> {ProcessStandard,ProcessExhaust,ProcessMoreToCome}* +* *ProcessStandard -> SinkStandard -> SinkWait -> Source (standard RPC)* +* *ProcessExhaust -> SinkMoreToCome-> SinkWait -> ProcessExhaust* +* *ProcessExhaust -> SinkFinal -> SinkWait -> Source* +* *ProcessMoreToCome -> Source* + +*Source* - When the server is in the state it requests a new message from the network to handle. + +*SourceWait* - This simply the waiting state for that requested message to arrive. The message that is received will also dictate which mode the *Process* state will be transitioned into. + +*Process* - The message enters through the [ServiceEntryPoint] and will be run through the database in this state. This state may operate in different modes (*Standard*, *Exhaust*, or *MoreToCome*) which dictate the next state transition. The *MoreToCome* mode denotes that another message should be received before any other action, and so the server returns to the *Source* state when *MoreToCome* mode is seen by the *Process* state on the request message. Meanwhile the *Exhaust* mode indicates that multiple messages must be sent back, and so it will continue to send more response messages until this state stops setting *MoreToCome* mode. + +*SinkWait* - Marks the period when the server waits for the database result to be sent over the network This state is usually preceded by a *Sink* state that follows three modes similar to *Process* (*Standard*, *MoreToCome*, *Final*). *Standard* and *Final* will simply proceed to the *SinkWait* stage to await the database result and then return to *Source*. If the *MoreToCome* mode is enabled, however, the server will go on to *ProcessExhaust* following the standard *SinkWait* state. When this happens the server will not transition back to *Source* until a message is received with *MoreToCome* disabled. + +*EndSession* - Denotes the end of a session. + +Should an error occur throughout the lifecycle, the state will transition to the *EndSession* state. + +In order to return the results to the user whether it be a document or a response code, MongoDB uses the [ReplyBuilderInterface]. This interface helps to build message bodies for replying to commands or even returning documents. + +This builder interface includes a standard BodyBuilder that builds reply messages in serialized-BSON format. + +A Document body builder ([DocSequenceBuilder]) is also defined to help build a reply that can be used to build a response centered around a document. + +The various builders supplied in the ReplyBuilderInterface can be appended together to generate responses containing document bodies, error codes, and other appropriate response types. + +This interface acts as a cursor to build a response message to be sent out back to the client. + +[ServiceExecutor]: service_executor.h +[ServiceStateMachine]: service_state_machine.h +[ServiceEntryPoint]: service_entry_point.h +[ServiceEntryPointImpl]: service_entry_point_impl.h +[ReplyBuilderInterface]: ../rpc/reply_builder_interface.h +[DocSequenceBuilder]: ../rpc/op_msg.h \ No newline at end of file -- cgit v1.2.1