Menene Bloom filter kuma wane alaaba da ya yi?

Question

Accepted Answer

**Bloom filter** shine tsarin **kuɗar-kuɗa** mai nauyin ajiya wanda ke amsa shugaba akan janguda ta saiti tare da jeri guda: zai iya samun **karɓi-jiya** amma **kuwa ba za a samun karɓi-tsira ba**. "Ba tare" tabbas ne; "Wataɗa jiya" yana buƙata ainihin bincike.

## Yadda ya aiki

Jerin bit na `m` bits da `k` ayyuka na hash. Don **ƙara** abu, saita `k` bits da ya ambaci shi. Don **bubugar**, bincika wadancan `k` bits — idan wani shine 0, abu shine tabbas ba jiya.

```text
bits: [0 0 0 0 0 0 0 0]
add "cat":  hash->bits 1,4,6  -> [0 1 0 0 1 0 1 0]
query "dog": hashes to 1,3,6 -> bit 3 is 0 -> DEFINITELY absent
query "cat": all of 1,4,6 set -> "probably present"
```

## Lambar

```python
class BloomFilter:
    def __init__(self, m, hashes):
        self.bits = [0]*m
        self.m, self.hashes = m, hashes   # list of hash fns
    def add(self, x):
        for h in self.hashes:
            self.bits[h(x) % self.m] = 1
    def __contains__(self, x):            # False = certain; True = maybe
        return all(self.bits[h(x) % self.m] for h in self.hashes)
```

| Aiki | Lokaci | Ajiya |
|---|---|---|
| add | O(k) | O(m) bits |
| query | O(k) | — |

Babu karɓi-jiya; cikin karɓi-kuɗa jiya ya fadi yayin `m` (da bunkura `k`) ya girma.

## Alaabu

- **Gajere:** natsewa kaɗan na ƙarfin ajiya ɗindan ajiye maɓuɓɓuka; aiki na lokaci-kwakwalwa.
- **Rauni:** karɓi-jiya; **ba za a kasuhe ba** (Bloom filter na gida); ba za a jera membobi ba.

## Me ya sa yana mahimmanci

Bloom filters sauƙi toshe aiki mai tsada: databases (misali Cassandra, HBase) suna amfani da su don sakewa karantar disk don maɓuɓɓuka da **tabbas** ba su kan disk.

Suna nuni abubuwa na tsarin dà ta gida—karɓi ƙarami, iyaka kuskure cikin musaya don babbar ragewa a ƙarfin ajiya da I/O.