}
        return numOfDeleted;
    }

    /**
     * Refreshes the specified index to make recent changes visible for search.
     * This operation ensures that all pending writes are persisted and searchable.
     *
     * @param searchEngineClient the search engine client to use for refresh
     * @param index the index name to refresh
     * @return the refresh status code
     */

            attemptCount.incrementAndGet();
            throw new RuntimeException("Persistent failure");
        });

        try {
            fesenClient.get(c -> mockFuture);
            fail("Expected exception after max retries");
        } catch (RuntimeException e) {
            assertEquals("Persistent failure", e.getMessage());
        }

        // Should try initial + maxRetryCount times (1 + 3 = 4)

**DataService**: Access result persistence, iteration

**Implementations**:
- `UrlQueueServiceImpl`, `DataServiceImpl`: In-memory (default)
- `OpenSearchDataService`: OpenSearch backend (persistent)

### Processing Pipeline

```
CrawlerThread → Client → ResponseProcessor → Transformer → Extractor → ExtractData
                                                                            ↓