Unresolved: Mapbox SDK connection pool exhaustion under concurrent tile loads

Answering the Core Question

When the Mapbox Android SDK throws MapboxException with the message "Connection pool exhausted" or "No connection available", it indicates that OkHttp’s default connection pool (5 idle sockets, 5‑minute keep‑alive) has been saturated by concurrent tile or geocoding requests. The SDK does not expose a public API to tune this pool, so the only supported way to avoid the error is to supply a custom OkHttpClient with a larger pool before the SDK is initialized.

Confirmed Facts

• Mapbox SDK internally creates an OkHttpClient with new ConnectionPool(5, 5, TimeUnit.MINUTES).
• High‑frequency map pans, zooms, or batch requests can quickly consume all 5 idle sockets, triggering IOException: Connection pool exhausted.
• Setting a custom client via Mapbox.getInstance().setOkHttpClient(client) is the only documented hook, though it is not prominently advertised.
• Internal retry logic retries immediately with no back‑off, which may exacerbate pool contention.
• OkHttp logs (e.g., via HttpLoggingInterceptor) are required to confirm the exact exception stack trace.

Likely Explanation

The default pool is too small for the request pattern in your app. Rapid tile requests outpace the pool’s ability to recycle sockets, so new connections are refused. Because the SDK’s retry interceptor fires immediately, the same exhausted socket pool is hit again, producing the generic network error.

Practical Steps to Mitigate

1. Enable OkHttp Logging (optional but recommended)

   ```java HttpLoggingInterceptor logger = new HttpLoggingInterceptor(); logger.setLevel(HttpLoggingInterceptor.Level.BODY); OkHttpClient client = new OkHttpClient.Builder() .addInterceptor(logger) .build(); ```

   Attach this client to the SDK before initializing any Mapbox component.

2. Configure a Larger ConnectionPool

   ```java ConnectionPool pool = new ConnectionPool(20, 10, TimeUnit.MINUTES); OkHttpClient client = new OkHttpClient.Builder() .connectionPool(pool) .build(); Mapbox.getInstance().setOkHttpClient(client); ```

   Increasing maxIdleConnections to 20 and keepAliveDuration to 10 minutes gives the SDK more headroom. Adjust these numbers based on observed usage and available device resources.

3. Ensure SDK Interceptors Remain Intact

   The custom client should still use the SDK’s default interceptors. Avoid replacing the entire client; instead, use the builder to add only the pool and logging interceptors. The SDK internally adds authentication, telemetry, and error‑handling interceptors.

4. Optional: Add Your Own Back‑off Retry

   If you need finer control, create a RetryInterceptor that applies exponential back‑off and add it *after* the SDK’s interceptors. Ensure you do not duplicate the SDK’s immediate retry logic.

   ```java client = client.newBuilder() .addInterceptor(new ExponentialBackoffInterceptor()) .build(); ```

5. Verify the Fix
   • Run a load test that mimics rapid panning or a batch geocoding call.
   • Check the log output for any remaining "Connection pool exhausted" exceptions.
   • Use pool.stats() or Android’s Network Stats API to confirm idle connections stay above zero during peak load.

Diagnostic Detail Needed

To tailor the recommendation further, please confirm whether you have already called Mapbox.getInstance().setOkHttpClient() before any Mapbox component (e.g., MapView, Navigation, Search) is instantiated. If the custom client is set after a component is created, the SDK will have already built its internal client and the pool size change will have no effect.

Summary

Increasing the OkHttp connection pool size via a custom client supplied to the SDK before initialization is the supported way to eliminate “Connection pool exhausted” errors under heavy concurrent tile loads. Adding back‑off logic can help, but must be coordinated with the SDK’s retry interceptor to avoid duplicate retries.