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expands number of erasure coding shreds in the last batch in slots (#16484)

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Number of parity coding shreds is always less than the number of data
shreds in FEC blocks:
https://github.com/solana-labs/solana/blob/6907a2366/ledger/src/shred.rs#L719

Data shreds are batched in chunks of 32 shreds each:
https://github.com/solana-labs/solana/blob/6907a2366/ledger/src/shred.rs#L714

However the very last batch of data shreds in a slot can be small, in
which case the loss rate can be exacerbated.

This commit expands the number of coding shreds in the last FEC block in
slots to: 64 - number of data shreds; so that FEC blocks are always 64
data and parity coding shreds each.

As a consequence of this, the last FEC block has more parity coding
shreds than data shreds. So for some shred indices we will have a coding
shred but no data shreds. This should not cause any kind of overlapping
FEC blocks as in:
https://github.com/solana-labs/solana/pull/10095
since this is done only for the very last batch in a slot, and the next
slot will reset the shred index.
This commit is contained in:
behzad nouri
2021-04-21 12:47:50 +00:00
committed by GitHub
parent ba2be0ca34
commit 37b8587d4e
14 changed files with 243 additions and 262 deletions
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7
ledger/tests/shred.rs
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@@ -22,9 +22,7 @@ type IndexShredsMap = BTreeMap<u32, Vec<Shred>>;
fn test_multi_fec_block_coding() {
let keypair = Arc::new(Keypair::new());
let slot = 0x1234_5678_9abc_def0;
let shredder = Shredder::new(slot, slot - 5, 1.0, keypair.clone(), 0, 0)
.expect("Failed in creating shredder");
let shredder = Shredder::new(slot, slot - 5, keypair.clone(), 0, 0).unwrap();
let num_fec_sets = 100;
let num_data_shreds = (MAX_DATA_SHREDS_PER_FEC_BLOCK * num_fec_sets) as usize;
let keypair0 = Keypair::new();
@@ -200,8 +198,7 @@ fn setup_different_sized_fec_blocks(
parent_slot: Slot,
keypair: Arc<Keypair>,
) -> (IndexShredsMap, IndexShredsMap, usize) {
let shredder =
Shredder::new(slot, parent_slot, 1.0, keypair, 0, 0).expect("Failed in creating shredder");
let shredder = Shredder::new(slot, parent_slot, keypair, 0, 0).unwrap();
let keypair0 = Keypair::new();
let keypair1 = Keypair::new();
let tx0 = system_transaction::transfer(&keypair0, &keypair1.pubkey(), 1, Hash::default());