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Diffstat (limited to 'src/bloom.h')
| -rw-r--r-- | src/bloom.h | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/src/bloom.h b/src/bloom.h index 9307257852..24dc607cd9 100644 --- a/src/bloom.h +++ b/src/bloom.h @@ -94,7 +94,18 @@ public: * insert()'ed ... but may also return true for items that were not inserted. * * It needs around 1.8 bytes per element per factor 0.1 of false positive rate. - * (More accurately: 3/(log(256)*log(2)) * log(1/fpRate) * nElements bytes) + * For example, if we want 1000 elements, we'd need: + * - ~1800 bytes for a false positive rate of 0.1 + * - ~3600 bytes for a false positive rate of 0.01 + * - ~5400 bytes for a false positive rate of 0.001 + * + * If we make these simplifying assumptions: + * - logFpRate / log(0.5) doesn't get rounded or clamped in the nHashFuncs calculation + * - nElements is even, so that nEntriesPerGeneration == nElements / 2 + * + * Then we get a more accurate estimate for filter bytes: + * + * 3/(log(256)*log(2)) * log(1/fpRate) * nElements */ class CRollingBloomFilter { |