fix: new variant hashing #533
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kwasniew
commented
Oct 30, 2023
| @@ -1,5 +1,23 @@ | |||
| import * as murmurHash3 from 'murmurhash3js'; | |||
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| export default function normalizedValue(id: string, groupId: string, normalizer = 100): number { | |||
| return (murmurHash3.x86.hash32(`${groupId}:${id}`) % normalizer) + 1; | |||
| function normalizedValue(id: string, | |||
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making this private since I want other code to use strategy or variant specific functions
kwasniew
commented
Oct 30, 2023
| const STRATEGY_SEED = 0; | ||
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| export function normalizedStrategyValue(id: string, groupId: string): number { | ||
| return normalizedValue(id, groupId, 100, STRATEGY_SEED); |
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It looks like existing code always assumes 100 for strategies
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I believe we do, because the percentage slider for our gradualRollouts are 0-100 %
kwasniew
commented
Oct 30, 2023
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| export function normalizedVariantValue(id: string, | ||
| groupId: string, | ||
| normalizer: number): number { |
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for variants we want to force the normalizer usage by the calling code
kwasniew
commented
Oct 30, 2023
| return normalizedValue(id, groupId, 100, STRATEGY_SEED); | ||
| } | ||
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| const VARIANT_SEED = 86028157; |
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I deliberate don't want this to leak out to the calling code
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What
Uses a new seed for ensuring a fair distribution for variants.
Background
After a customer reported that variant distribution seemed skewed we performed some testing and found that since we use the same hash string for both gradual rollout and variant allocation we'd reduced the set of groups we could get to whatever percentage our gradual rollout was set.
Example
Take a gradualRollout of 10%, this will select normalized hashes between 1 and 10, when we then again hash the same string that gave us between 1 and 10, but with modulo 1000 for variants, this will only give us 100 possible groups, instead of the expected 1000.
Fix
Force the normalization to accept a seed, and make sure to use a new seed when normalizing the variant distribution hash.
Worth noting
This will require release of a new major version, since we are changing how hashing works.