45 lines
2.6 KiB
Markdown
45 lines
2.6 KiB
Markdown
# Gossip, A.K.A. Cluster Info
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This RFC describes the Solana's gossip protocol, also known as the network control plane.
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Nodes continuously share signed data objects among themselves in order to find each other, structure the network data plane, prevent censoring, etc.
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The basic mechanism is a 10Hz loop wherein every node sends a push message and/or a pull message. Push and pull messages may elicit responses, and push messages may be forwarded on to others in the network.
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Gossip runs on a well-known UDP/IP port, or a port in a well-known range. Once a network is bootstrapped, nodes advertise to each other where to find their gossip endpoint (a socket address).
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## Gossip Records
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Records shared over gossip are arbitrary, but signed and versioned (with a timestamp), and need to make sense to the node receiving them. A strategy of "most recent timestamp wins" is employed to manage what's stored in cluster info. If 2 values from the same creator have the same timestamp, the value with the greater hash wins.
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## Push
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### Push Message
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A push message is "hey network, I have something new to share". Nodes send push messages to `PUSH_FANOUT` push peers.
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Upon receiving a push message, a node examines the message for:
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1. duplication: if the message has been seen before, the node responds with `PushMessagePrune` and drops the message
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2. new info: if the message is new the node
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a. stores the new information with an updated version in its cluster info
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b. stores the message in `pushed_once` (used for detecting duplicates, purged after `PUSH_MSG_TIMEOUT * 5` ms)
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c. retransmits the messages to its own push peers
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3. expiration: nodes drop push messages that are older than `PUSH_MSG_TIMEOUT`
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### Push Peers, Prune Message
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A nodes selects its push peers at random from the active set of known peers. The node keeps this selection for a relatively long time. When a prune message is received, the node drops the push peer that sent the prune. Prune is an indication that there is another, faster path to that node than direct push.
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The set of push peers is kept fresh by rotating a new node into the set every `PUSH_MSG_TIMEOUT/2` milliseconds.
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## Pull
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### Pull Message
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A pull message is "hey dude, got anything new?". A pull message is sent to a single peer at random and comprises a Bloom filter that represents "things I already have". A node receiving a pull message iterates over its values and constructs a pull response of things that miss the filter and would fit in a message.
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A node constructs the pull Bloom filter by iterating over the values it currently has.
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