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adds new CrdsFilterSet type for Vec<CrdsFilter> (#12029)

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behzad nouri 2020-09-04 13:04:47 +00:00 committed by GitHub
parent e2aaa6706c
commit 114c211b66
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1 changed files with 48 additions and 60 deletions
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108
core/src/crds_gossip_pull.rs
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@ -58,48 +58,6 @@ impl CrdsFilter {
}
}
// CrdsFilter::new_complete_set returns a vector of filters. Given a hash
// value, this function returns the filter within that vector which
// corresponds to the item.
// TODO: Consider making Vec<CrdsFilter> a separate type, and implementing
// this (and new_complete_set) function as methods on that type.
pub fn get_crds_filter<'a>(
filters: &'a mut Vec<CrdsFilter>,
item: &Hash,
) -> Option<&'a mut CrdsFilter> {
if let Some(filter) = filters.first() {
let shift = 64 - filter.mask_bits.min(64);
let index = CrdsFilter::hash_as_u64(item)
.checked_shr(shift)
.unwrap_or(0u64);
filters.get_mut(index as usize)
} else {
None
}
}
// generates a vec of filters that together hold a complete set of Hashes
pub fn new_complete_set(num_items: usize, max_bytes: usize) -> Vec<Self> {
// Note: get_crds_filter above relies on the order of filters and
// bit-mask pattern here. If changed, update get_crds_filter
// accordingly.
let max_bits = (max_bytes * 8) as f64;
let max_items = Self::max_items(max_bits, FALSE_RATE, KEYS);
let mask_bits = Self::mask_bits(num_items as f64, max_items as f64);
// for each possible mask combination, generate a new filter.
let mut filters = vec![];
for seed in 0..2u64.pow(mask_bits) {
let filter = Bloom::random(max_items as usize, FALSE_RATE, max_bits as usize);
let mask = Self::compute_mask(seed, mask_bits);
let filter = CrdsFilter {
filter,
mask,
mask_bits,
};
filters.push(filter)
}
filters
}
fn compute_mask(seed: u64, mask_bits: u32) -> u64 {
assert!(seed <= 2u64.pow(mask_bits));
let seed: u64 = seed.checked_shl(64 - mask_bits).unwrap_or(0x0);
@ -149,6 +107,39 @@ impl CrdsFilter {
}
}
/// A vector of crds filters that together hold a complete set of Hashes.
struct CrdsFilterSet(Vec<CrdsFilter>);
impl CrdsFilterSet {
fn new(num_items: usize, max_bytes: usize) -> Self {
let max_bits = (max_bytes * 8) as f64;
let max_items = CrdsFilter::max_items(max_bits, FALSE_RATE, KEYS);
let mask_bits = CrdsFilter::mask_bits(num_items as f64, max_items as f64);
// For each possible mask combination, generate a new filter.
let seeds = 0..2u64.pow(mask_bits);
let filters = seeds.map(|seed| {
let filter = Bloom::random(max_items as usize, FALSE_RATE, max_bits as usize);
let mask = CrdsFilter::compute_mask(seed, mask_bits);
CrdsFilter {
filter,
mask,
mask_bits,
}
});
Self(filters.collect())
}
// Returns the filter within the vector of crds filters which corresponds
// to the given hash value.
fn get(&mut self, hash_value: &Hash) -> Option<&mut CrdsFilter> {
let shift = 64 - self.0.first()?.mask_bits.min(64);
let index = CrdsFilter::hash_as_u64(hash_value)
.checked_shr(shift)
.unwrap_or(0u64);
self.0.get_mut(index as usize)
}
}
#[derive(Default)]
pub struct ProcessPullStats {
pub success: usize,
@ -385,9 +376,9 @@ impl CrdsGossipPull {
CRDS_GOSSIP_DEFAULT_BLOOM_ITEMS,
crds.table.values().count() + self.purged_values.len(),
);
let mut filters = CrdsFilter::new_complete_set(num, bloom_size);
let mut filters = CrdsFilterSet::new(num, bloom_size);
let mut add_value_hash = |value_hash| {
if let Some(filter) = CrdsFilter::get_crds_filter(&mut filters, value_hash) {
if let Some(filter) = filters.get(value_hash) {
debug_assert!(filter.test_mask(value_hash));
filter.filter.add(value_hash);
}
@ -399,7 +390,7 @@ impl CrdsGossipPull {
add_value_hash(&value_hash);
}
filters
filters.0
}
/// filter values that fail the bloom filter up to max_bytes
@ -643,23 +634,21 @@ mod test {
}
#[test]
fn test_crds_filter_get_crds_filter() {
let mut filters =
CrdsFilter::new_complete_set(/*num_items=*/ 9672788, /*max_bytes=*/ 8196);
assert_eq!(filters.len(), 1024);
let mut bytes = [0u8; HASH_BYTES];
fn test_crds_filter_set_get() {
let mut crds_filter_set =
CrdsFilterSet::new(/*num_items=*/ 9672788, /*max_bytes=*/ 8196);
assert_eq!(crds_filter_set.0.len(), 1024);
let mut rng = thread_rng();
for _ in 0..100 {
let mut bytes = [0u8; HASH_BYTES];
rng.fill_bytes(&mut bytes);
let hash_value = Hash::new(&bytes);
let filter = CrdsFilter::get_crds_filter(&mut filters, &hash_value)
.unwrap()
.clone();
let filter = crds_filter_set.get(&hash_value).unwrap().clone();
assert!(filter.test_mask(&hash_value));
// Validate that the returned filter is the *unique* filter which
// corresponds to the hash value (i.e. test_mask returns true).
let mut num_hits = 0;
for f in &filters {
for f in &crds_filter_set.0 {
if *f == filter {
num_hits += 1;
assert!(f.test_mask(&hash_value));
@ -672,11 +661,10 @@ mod test {
}
#[test]
fn test_crds_filter_new_complete_set() {
// Validates invariances required by CrdsFilter::get_crds_filter in the
// vector of filters generated by CrdsFilter::new_complete_set.
let filters =
CrdsFilter::new_complete_set(/*num_items=*/ 55345017, /*max_bytes=*/ 4098);
fn test_crds_filter_set_new() {
// Validates invariances required by CrdsFilterSet::get in the
// vector of filters generated by CrdsFilterSet::new.
let filters = CrdsFilterSet::new(/*num_items=*/ 55345017, /*max_bytes=*/ 4098).0;
assert_eq!(filters.len(), 16384);
let mask_bits = filters[0].mask_bits;
let right_shift = 64 - mask_bits;
@ -1039,7 +1027,7 @@ mod test {
}
#[test]
fn test_crds_filter_complete_set_add_mask() {
let mut filters = CrdsFilter::new_complete_set(1000, 10);
let mut filters = CrdsFilterSet::new(1000, 10).0;
assert!(filters.iter().all(|f| f.mask_bits > 0));
let mut h: Hash = Hash::default();
// rev to make the hash::default() miss on the first few test_masks