Store nodes that timed out in a rolling bloom filter

[dnsseed-rust] / src / bloom.rs

diff --git a/src/bloom.rs b/src/bloom.rs
new file mode 100644 (file)
index 0000000..7255876
--- /dev/null
+++ b/src/bloom.rs
@@ -0,0 +1,143 @@
+use std::collections::hash_map::RandomState;
+use std::hash::{BuildHasher, Hash, Hasher};
+use std::time::{Duration, Instant};
+use std::marker::PhantomData;
+
+// Constants for roughly 1 in 1 million fp with 18m entries
+/// Number of entries in the filter (each 4 bits). 256MiB in total.
+const FILTER_SIZE: usize = 64 * 1024 * 1024 * 8;
+const HASHES: usize = 27;
+const ROLL_COUNT: usize = 1_240_000;
+#[cfg(test)]
+const GENERATION_BITS: usize = 2;
+#[cfg(not(test))]
+const GENERATION_BITS: usize = 4;
+pub const GENERATION_COUNT: usize = (1 << GENERATION_BITS) - 1;
+const ELEMENTS_PER_BYTE: usize = 8 / GENERATION_BITS;
+
+pub struct RollingBloomFilter<T: Hash> {
+       last_roll: Instant,
+       inserted_in_last_generations: [usize; GENERATION_COUNT - 1],
+       inserted_since_last_roll: usize,
+       current_generation: u8,
+       bits: Vec<u8>,
+       hash_keys: [RandomState; HASHES],
+       _entry_type: PhantomData<T>,
+}
+
+impl<T: Hash> RollingBloomFilter<T> {
+       pub fn new() -> Self {
+               let mut bits = Vec::new();
+               bits.resize(FILTER_SIZE * GENERATION_BITS / 8, 0);
+               Self {
+                       last_roll: Instant::now(),
+                       inserted_since_last_roll: 0,
+                       inserted_in_last_generations: [0; GENERATION_COUNT - 1],
+                       current_generation: 1,
+                       bits,
+                       hash_keys: [RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(),
+                                   RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(),
+                                   RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(),
+                                   RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(),
+                                   RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(), RandomState::new(),
+                                   RandomState::new(), RandomState::new()],
+                       _entry_type: PhantomData,
+               }
+       }
+
+       pub fn contains(&self, item: &T) -> bool {
+               for state in self.hash_keys.iter() {
+                       let mut hasher = state.build_hasher();
+                       item.hash(&mut hasher);
+                       let idx = hasher.finish() as usize;
+
+                       let byte = self.bits[(idx / ELEMENTS_PER_BYTE) % (FILTER_SIZE / 8)];
+                       let bits_shift = (idx % ELEMENTS_PER_BYTE) * GENERATION_BITS;
+                       let bits = (byte & ((GENERATION_COUNT as u8) << bits_shift)) >> bits_shift;
+                       if bits == 0 { return false; }
+               }
+               true
+       }
+
+       pub fn get_element_count(&self) -> [usize; GENERATION_COUNT] {
+               let mut res = [0; GENERATION_COUNT];
+               res[0..(GENERATION_COUNT-1)].copy_from_slice(&self.inserted_in_last_generations);
+               *res.last_mut().unwrap() = self.inserted_since_last_roll;
+               res
+       }
+
+       pub fn insert(&mut self, item: &T, roll_duration: Duration) {
+               if Instant::now() - self.last_roll > roll_duration / GENERATION_COUNT as u32 ||
+                  self.inserted_since_last_roll > ROLL_COUNT {
+                       self.current_generation += 1;
+                       if self.current_generation == GENERATION_COUNT as u8 + 1 { self.current_generation = 1; }
+                       let remove_generation = self.current_generation;
+
+                       for idx in 0..FILTER_SIZE {
+                               let byte = &mut self.bits[(idx / ELEMENTS_PER_BYTE) % (FILTER_SIZE / 8)];
+                               let bits_shift = (idx % ELEMENTS_PER_BYTE) * GENERATION_BITS;
+                               let bits = (*byte & ((GENERATION_COUNT as u8) << bits_shift)) >> bits_shift;
+
+                               if bits == remove_generation {
+                                       *byte &= !((GENERATION_COUNT as u8) << bits_shift);
+                               }
+                       }
+                       self.last_roll = Instant::now();
+                       let mut new_generations = [0; GENERATION_COUNT - 1];
+                       new_generations[0..GENERATION_COUNT - 2].copy_from_slice(&self.inserted_in_last_generations[1..]);
+                       new_generations[GENERATION_COUNT - 2] = self.inserted_since_last_roll;
+                       self.inserted_in_last_generations = new_generations;
+                       self.inserted_since_last_roll = 0;
+               }
+
+               for state in self.hash_keys.iter() {
+                       let mut hasher = state.build_hasher();
+                       item.hash(&mut hasher);
+                       let idx = hasher.finish() as usize;
+
+                       let byte = &mut self.bits[(idx / ELEMENTS_PER_BYTE) % (FILTER_SIZE / 8)];
+                       let bits_shift = (idx % ELEMENTS_PER_BYTE) * GENERATION_BITS;
+                       *byte &= !((GENERATION_COUNT as u8) << bits_shift);
+                       *byte |= self.current_generation << bits_shift;
+               }
+               self.inserted_since_last_roll += 1;
+       }
+}
+
+#[test]
+fn test_bloom() {
+       let mut filter = RollingBloomFilter::new();
+       for i in 0..1000 {
+               filter.insert(&i, Duration::from_secs(60 * 60 * 24));
+       }
+       for i in 0..1000 {
+               assert!(filter.contains(&i));
+       }
+       for i in 1000..2000 {
+               assert!(!filter.contains(&i));
+       }
+       assert_eq!(filter.get_element_count(), [0, 0, 1000]);
+       filter.inserted_since_last_roll = ROLL_COUNT + 1;
+       filter.insert(&1000, Duration::from_secs(60 * 60 * 24));
+       assert_eq!(filter.get_element_count(), [0, ROLL_COUNT + 1, 1]);
+       for i in 0..1001 {
+               assert!(filter.contains(&i));
+       }
+       filter.inserted_since_last_roll = ROLL_COUNT + 1;
+       for i in 1001..2000 {
+               filter.insert(&i, Duration::from_secs(60 * 60 * 24));
+       }
+       assert_eq!(filter.get_element_count(), [ROLL_COUNT + 1, ROLL_COUNT + 1, 999]);
+       for i in 0..2000 {
+               assert!(filter.contains(&i));
+       }
+       filter.inserted_since_last_roll = ROLL_COUNT + 1;
+       filter.insert(&2000, Duration::from_secs(60 * 60 * 24));
+       assert_eq!(filter.get_element_count(), [ROLL_COUNT + 1, ROLL_COUNT + 1, 1]);
+       for i in 0..1000 {
+               assert!(!filter.contains(&i));
+       }
+       for i in 1000..2001 {
+               assert!(filter.contains(&i));
+       }
+}