Transaction Validation Unit in a Solana Validator

TVU (Transaction Validation Unit) is the logic of the validator responsible for propagating blocks between validators and ensuring that those blocks' transactions reach the replay stage. Its principal external interface is the turbine protocol.

Retransmit Stage

TVU sockets

Externally, TVU UDP receiver appears to bind to one port, typically 8002 UDP. Internally, TVU is actually bound with multiple sockets to improve kernel's handling of the packet queues.

NOTE: TPU sockets use similar logic

A node advertises one external ip/port for TVU while binding multiple sockets to that same port:

let (tvu_port, tvu_sockets) = multi_bind_in_range_with_config(
    bind_ip_addr,
    port_range,
    socket_config,
    num_tvu_sockets.get(),
)
.expect("tvu multi_bind");

multi_bind_in_range_with_config sets SO_REUSEPORT. This means that other nodes only need to know about the one ip/port pair for TVU (similar principle applies in the case of TPU UDP sockets). The kernel distributes the incoming packets to all sockets bound to that port, and each socket can be serviced by a different thread.

NOTE: TVU QUIC socket does not use SO_REUSEPORT, but otherwise works similarly to UDP

The TVU socket information is published via Gossip and is available in the ContactInfo struct. To set a TVU socket, the node calls set_tvu(...). The set_tvu() method is created by the macro set_socket!. For example:

info.set_tvu(QUIC, (addr, tvu_quic_port)).unwrap();
info.set_tvu(UDP, (addr, tvu_udp_port)).unwrap();

Under the hood, set_tvu() calls set_socket().

In the ContactInfo struct, all sockets are identified by a tag/key, e.g.:

const SOCKET_TAG_TVU: u8 = 10;       // For UDP
const SOCKET_TAG_TVU_QUIC: u8 = 11;  // For QUIC

• set_socket() creates a SocketEntry and stores that into ContactInfo::sockets
• set_socket() updates ContactInfo::cache

cache: [SocketAddr; SOCKET_CACHE_SIZE]

cache is purely for quick lookups and optimization; it is not serialized and sent to peer nodes. SocketEntry is serialized and sent to peer nodes within the gossip message type CrdsData::ContactInfo. Upon receiving the ContactInfo, the peer node calls the get_socket! macro to retrieve the TVU port associated with the node. For example, to retrieve the TVU ports of the remote node, the peer node calls:

get_socket!(tvu, SOCKET_TAG_TVU, SOCKET_TAG_TVU_QUIC);