Configure CMAB for the Android SDK
The CMAB cache stores variation assignments to reduce latency and minimize API calls to the CMAB service.
Prerequisites
- Android SDK version 5.1.0 or higher.
- A CMAB-enabled experiment in your Optimizely project.
Minimum SDK version
5.1.0
Description
When a user is bucketed into a CMAB experiment, the Android SDK makes an API call to the CMAB service to determine which variation to show. To improve performance and reduce latency, the Android SDK caches these decisions based on the following:
- User ID
- Experiment ID
- CMAB attribute values
The cache is automatically invalidated when CMAB attributes change for a user, ensuring fresh decisions when context changes.
By default, the SDK uses an in-memory Least Recently Used (LRU) cache with a maximum size of 100 entries and a TTL of 30 minutes (1,800 seconds). You can customize these settings or provide your own cache implementation.
Configuration options
Configure CMAB when building your OptimizelyManager.
Default configuration
The Android SDK uses the following default values when no custom configuration is provided:
Setting | Default Value | Description |
|---|---|---|
Cache Size | 100 | Maximum number of cached decisions. |
Cache TTL | 1,800 seconds (30 minutes) | Time-to-live for cache entries. |
CmabClient | DefaultCmabClient | This network client implements the CmabClient interface to fetch real-time decisions from Optimizely's CMAB service. |
CmabPredictionEndpoint | This setting overrides the default prediction endpoint URL. It must include a %s placeholder for the CMAB experiment ID. |
Configuration methods
Set cache size
OptimizelyManager.builder().withCmabCacheSize(int cacheSize)Parameters
- cacheSize (int) – Maximum number of decisions to cache. Must be a positive integer.
Example
OptimizelyManager optimizelyManager = OptimizelyManager.builder()
.withCmabCacheSize(50)
.build(context);Set cache TTL
DefaultCmabService.builder().withCmabCacheTimeout(int interval, TimeUnit timeUnit)Parameters
- interval (int) – the interval.
- timeUnit (TimeUnit) – the time unit of the timeout argument.
Example
OptimizelyManager optimizelyManager = OptimizelyManager.builder()
.withCmabCacheTimeout(10, TimeUnit.SECONDS)
.build(context);Set custom CMABClient
DefaultCmabService.builder().withCmabClient(CmabClient cmabClient)Parameters
- cmabClient (CmabClient) – The custom implementation of the CmabClient interface.
Example
OptimizelyManager optimizelyManager = OptimizelyManager.builder()
.withCmabClient(customCmabClient)
.build(context);Set custom CMABPredictionEndpoint
DefaultCmabService.builder().withCmabPredictionEndpoint(String endpoint)Parameters
- endpoint (String) – The custom CMAB prediction endpoint.
Example
OptimizelyManager optimizelyManager = OptimizelyManager.builder()
.withCmabPredictionEndpoint("https://example-prediction.com/%s")
.build(context);Cache behavior
Automatic cache invalidation
The cache is automatically invalidated when the following occurs:
- The cached entry's TTL expires.
- CMAB attribute values change for a user (detected through MD5 hash comparison).
- The IGNORE_CMAB_CACHE decide option is used.
- The INVALIDATE_USER_CMAB_CACHE decide option is used.
- The RESET_CMAB_CACHE decide option is used.
CMAB-specific decide options
Control cache behavior on a per-decision basis using decide options.
// Ignore cache for this decision (always fetch fresh)
user.decideAsync(
"my-flag",
Arrays.asList(OptimizelyDecideOption.IGNORE_CMAB_CACHE),
(OptimizelyDecision decision) -> {
Log.d("Samples","[CMAB] async decision for cmab: " + decision.toString());
}
);
// Invalidate cached decision for this user and experiment
user.decideAsync(
"my-flag",
Arrays.asList(OptimizelyDecideOption.INVALIDATE_USER_CMAB_CACHE),
(OptimizelyDecision decision) -> {
Log.d("Samples","[CMAB] async decision for cmab: " + decision.toString());
}
);
// Clear entire CMAB cache
user.decideAsync(
"my-flag",
Arrays.asList(OptimizelyDecideOption.RESET_CMAB_CACHE),
(OptimizelyDecision decision) -> {
Log.d("Samples","[CMAB] async decision for cmab: " + decision.toString());
}
);Available CMAB decideOptions
Decide option | Description |
|---|---|
IGNORE_CMAB_CACHE | Bypass cache and fetch a fresh decision from CMAB service. |
INVALIDATE_USER_CMAB_CACHE | Remove cached decision for this user and experiment before deciding. |
RESET_CMAB_CACHE | Clear all entries from the CMAB cache before deciding. |