/// For each layer, returns the closest diff less than or equal to `slot`.

// Test that the diffs and snapshots required for storage of split states are retained in the

// hot DB as the split slot advances, if we begin from an initial configuration where this

// invariant holds.

fn test_slots_retained_invariant(hierarchy: HierarchyModuli, start_slot: u64, epoch_jump: u64) {

let start_slot = Slot::new(start_slot);

let mut finalized_slot = start_slot;

// Initially we have just one snapshot stored at the `start_slot`. This is what checkpoint

// sync sets up (or the V24 migration).

let mut retained_slots = vec![finalized_slot];

// Iterate until we've reached two snapshots in the future.

let stop_at = hierarchy

.next_snapshot_slot(hierarchy.next_snapshot_slot(start_slot).unwrap() + 1)

.unwrap();

while finalized_slot <= stop_at {

// Jump multiple epocsh at a time because inter-epoch states are not interesting and

// would take too long to iterate over.

let new_finalized_slot = finalized_slot + 32 * epoch_jump;

let new_retained_slots = hierarchy.closest_layer_points(new_finalized_slot, start_slot);

for slot in &new_retained_slots {

// All new retained slots must either be already stored prior to the old finalized

// slot, OR newer than the finalized slot (i.e. stored in the hot DB as part of

// regular state storage).

assert!(retained_slots.contains(slot) || *slot >= finalized_slot);

}

retained_slots = new_retained_slots;

finalized_slot = new_finalized_slot;

}

}

#[test]

fn slots_retained_invariant() {

let cases = [

// Default hierarchy with a start_slot between the 2^13 and 2^16 layers.

(

HierarchyConfig::default().to_moduli().unwrap(),

2 * (1 << 14) - 5 * 32,

1,

),

// Default hierarchy with a start_slot between the 2^13 and 2^16 layers, with 8 epochs

// finalizing at a time (should not make any difference).

(

HierarchyConfig::default().to_moduli().unwrap(),

2 * (1 << 14) - 5 * 32,

8,

),

// Very dense hierarchy config.

(

HierarchyConfig::from_str("5,7")

.unwrap()

.to_moduli()

.unwrap(),

32,

1,

),

// Very dense hierarchy config that skips a whole snapshot on its first finalization.

(

HierarchyConfig::from_str("5,7")

.unwrap()

.to_moduli()

.unwrap(),

32,

1 << 7,

),

];

for (hierarchy, start_slot, epoch_jump) in cases {

test_slots_retained_invariant(hierarchy, start_slot, epoch_jump);

}

}