Server Persistent Assignment

Persistent assignment allows you to ensure that a user's variant stays consistent while an experiment is running, regardless of changes to allocation or targeting.

Persistent Storage Adapter

The persistent storage adapter allows you to plug in your own storage solution that Statsig SDK uses to persist user assignments. The storage interface consists of just a load and save API for read/write operations.

info

Currently only supported in Go, Ruby, Legacy Node, Node Core, Kotlin, .Net, Python Core

Persistent Storage Logic

• Providing a storage adapter on Statsig initialization will give the SDK access to read & write on your custom storage
• Providing user persisted values to get_experiment will inform the SDK to
  • save the evaluation of the current user on first evaluation
    • Will only save when experiment / layer is active
  • load the previously saved evaluation of a persisted user on subsequent evaluations
• CAVEAT Persisted Value will be deleted when:
  • When you provided call getExperiment with user_persisted_values=None
  • or When experiment is not active

Persistent Assignment Options (Limited SDK Support)

• Enforce Targeting: boolean, default: false
  • Whether or not to enforce targeting rules before assigning persisted values

Node JS

val options = GetExperimentOptions(
  ...
  persistentAssignmentOptions = PersistentAssignmentOptions(
    enforceTargeting = true,
  )
)

Kotlin

const options: GetExperimentOptions = {
  ...
  persistentAssignmentOptions: {
    enforceTargeting: true,
  }
}

Example usage

Python (Python Core)

Statsig.initialize(
  'secret-key',
  StatsigOptions.new(
    user_persistent_storage: DummyPersistentStorageAdapter.new
  )
)
persisted_user = StatsigUser.new({ 'userID' => 'test-123' })
exp = Statsig.get_experiment( # User gets saved to persisted storage
  persisted_user,
  'active_experiment',
  Statsig::GetExperimentOptions.new(
    user_persisted_values: Statsig.get_user_persisted_values(persisted_user, 'userID')
  )
)
puts exp.group_name # 'Control'
exp = Statsig.get_experiment( # User evaluates using values from persisted storage
  StatsigUser.new({'userID' => 'unknown'}),
  'active_experiment',
  Statsig::GetExperimentOptions.new(
    user_persisted_values: Statsig.get_user_persisted_values(persisted_user, 'userID')
  )
)
puts exp.group_name # 'Control'

Node Core

from statsig_python_core import Statsig, StatsigUser, StatsigOptions, ExperimentEvaluationOptions, PersistentStorage

options = StatsigOptions(persistent_storage = MyPersistentStorage())
statsig = Statsig.initialize(options).wait
user = StatsigUser("a-user")
exp = statsig.get_experiment(StatsigUser("a-user"), ExperimentEvaluationOptions(user_persisted_values= PersistentStorage.get_user_persisted_value(user, "user_id")))
print(f"{exp.group_name}") # control

Node JS

import { PersistentStorage, StickyValues, UserPersistedValues } from '@statsig/statsig-node-core';

class MyPersistentStorage implements PersistentStorage {
  private storage = new Map<string, UserPersistedValues>();

  load(key: string): UserPersistedValues | null {
    return this.storage.get(key) || null;
  }

  save(key: string, config_name: string, data: StickyValues): void {
    const existing = this.storage.get(key) || {};
    existing[config_name] = data;
    this.storage.set(key, existing);
  }

  delete(key: string, config_name: string): void {
    const existing = this.storage.get(key);
    if (existing) {
      delete existing[config_name];
      this.storage.set(key, existing);
    }
  }
}

Kotlin

runBlocking {
  Statsig.initialize(
    "secret-key",
    StatsigOptions(userPersistentStorage = MyPersistentStorageAdapter())
  )
}
val persistedUser = StatsigUser("test-123")
var exp = Statsig.getExperimentSync(
  persistedUser,
  "active_experiment",
  GetExperimentOptions(
    userPersistedValues = Statsig.getUserPersistedValues(persistedUser, "userID"),
  ),
)
println(exp.groupName) // "Control"
exp = Statsig.getExperimentSync(
  StatsigUser("unknown"),
  "active_experiment",
  GetExperimentOptions(
    userPersistedValues = Statsig.getUserPersistedValues(persistedUser, "userID"),
  ),
)
println(exp.groupName) // "Control"

Ruby

await Statsig.initialize(
  "secret-key",
  {
    userPersistentStorage: new MyPersistentStorageAdapter() 
  }
)
const persistedUser: StatsigUser = { userID: "123" }
let exp = Statsig.getExperimentSync(
  persistedUser,
  "active_experiment",
  { 
    userPersistedValues: Statsig.getUserPersistedValues(user, "userID")
  },
)
console.log(exp.getGroupName()) // "Control"
exp = Statsig.getExperimentSync(
  { userID: "unknown" },
  "active_experiment",
  { 
    userPersistedValues: Statsig.getUserPersistedValues(user, "userID")
  },
)
console.log(exp.getGroupName()) // "Control"

Go

InitializeWithOptions(
  "secret-key",
  &Options{
    UserPersistentStorage: persistentStorage,
  }
)
persistedUser := User{UserID: "123"}
exp := GetExperimentWithOptions(
  persistedUser,
  "active_experiment",
  &GetExperimentOptions{
    PersistedValues: GetUserPersistedValues(persistedUser, "userID")
  }
)
fmt.Println(exp.GroupName) // "Control"
exp = GetExperimentWithOptions(
  User{UserID: "unknown"},
  "active_experiment",
  &GetExperimentOptions{
    PersistedValues: GetUserPersistedValues(persistedUser, "userID")
  }
)
fmt.Println(exp.GroupName) // "Control"

.Net

var options = new StatsigServerOptions();
options.UserPersistentStorage = new MyPersistentStorageAdapter()
await StatsigServer.Initialize("server-secret-key", options);

var persistedUser = new StatsigUser { UserID = "123" };
var values = await StatsigServer.GetUserPersistedValues(persistedUser, "userID");
var getExpOptions = new StatsigGetExperimentOptions(values);
var exp = StatsigServer.GetExperimentSync(persistedUser, "active_experiment", getExpOptions);
Console.WriteLine(exp.GroupName); // "Control"

var newValues = await StatsigServer.GetUserPersistedValues(persistedUser, "userID");
var newGetExpOptions = StatsigGetExperimentOptions(newValues);

var newExp = StatsigServer.GetExperimentSync(new StatsigUser {UserID = "unknown"}, "active_experiment", newGetExpOptions);
Console.WriteLine(newExp.GroupName); // "Control"