Module solana::erasure

Erasure Coding and Recovery

Blobs are logically grouped into erasure sets or blocks. Each set contains 16 sequential data blobs and 4 sequential coding blobs.

Coding blobs in each set starting from start_idx: For each erasure set: generate NUM_CODING coding_blobs. index the coding blobs from start_idx to start_idx + NUM_CODING - 1.

model of an erasure set, with top row being data blobs and second being coding |<======================= NUM_DATA ==============================>| |<==== NUM_CODING ===>| +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | D | | D | | D | | D | | D | | D | | D | | D | | D | | D | +---+ +---+ +---+ +---+ +---+ . . . +---+ +---+ +---+ +---+ +---+ | C | | C | | C | | C | | | | | | | | | | | | | +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+

blob structure for coding blobs

• ------- meta is set and used by transport, meta.size is actual length | of data in the byte array blob.data | | + -- data is stuff shipped over the wire, and has an included | | header V V +----------+------------------------------------------------------------+ | meta | data | |+---+-- |+---+---+---+---+------------------------------------------+| || s | . || i | | f | s | || || i | . || n | i | l | i | || || z | . || d | d | a | z | blob.data(), or blob.data_mut() || || e | || e | | g | e | || |+---+-- || x | | s | | || | |+---+---+---+---+------------------------------------------+| +----------+------------------------------------------------------------+ | |<=== coding blob part for "coding" =======>| | | |<============== data blob part for "coding" ==============>|

Structs

CodingGenerator	Generates coding blobs on demand given data blobs
ErasureConfig
Session	Represents an erasure "session" with a particular configuration and number of data and coding blobs

Constants

ERASURE_SET_SIZE	Total number of blobs in an erasure set; includes data and coding blobs
NUM_CODING	Number of coding blobs; also the maximum number that can go missing.
NUM_DATA	Number of data blobs