Module solana_ledger::shred
source · [−]Expand description
The shred module defines data structures and methods to pull MTU sized data frames from the
network. There are two types of shreds: data and coding. Data shreds contain entry information
while coding shreds provide redundancy to protect against dropped network packets (erasures).
+———————————————————————————————+ | Data Shred | +———————————————————————————————+ | common | data | payload | | header | header | | |+—+—+— |+—+—+—|+–––––––––––––––––––––––––––––+––+| || s | s | . || p | f | s || data (ie ledger entries) | r || || i | h | . || a | l | i || | e || || g | r | . || r | a | z || See notes immediately after shred diagrams for an | s || || n | e | || e | g | e || explanation of the “restricted” section in this payload | t || || a | d | || n | s | || | r || || t | | || t | | || | i || || u | t | || | | || | c || || r | y | || o | | || | t || || e | p | || f | | || | e || || | e | || f | | || | d || |+—+—+— |+—+—+—+|–––––––––––––––––––––––––––––+––+| +———————————————————————————————+
+———————————————————————————————+ | Coding Shred | +———————————————————————————————+ | common | coding | payload | | header | header | | |+—+—+— |+—+—+—+––––––––––––––––––––––––––––––––+| || s | s | . || n | n | p || data (encoded data shred data) || || i | h | . || u | u | o || || || g | r | . || m | m | s || || || n | e | || | | i || || || a | d | || d | c | t || || || t | | || | | i || || || u | t | || s | s | o || || || r | y | || h | h | n || || || e | p | || r | r | || || || | e | || e | e | || || || | | || d | d | || || |+—+—+— |+—+—+—+|+–––––––––––––––––––––––––––––––+| +———————————————————————————————+
Notes: a) Coding shreds encode entire data shreds: both of the headers AND the payload. b) Coding shreds require their own headers for identification and etc. c) The erasure algorithm requires data shred and coding shred bytestreams to be equal in length.
So, given a) - c), we must restrict data shred’s payload length such that the entire coding payload can fit into one coding shred / packet.
Structs
The coding shred header has FEC information
The data shred header has parent offset and flags
A common header that is present in data and code shred headers
Tuple which uniquely identifies a shred should it exists.
Enums
Constants
The following constants are computed by hand, and hardcoded.
test_shred_constants ensures that the values are correct.
Constants are used over lazy_static for performance reasons.