Amazon OpenSearch Service is correct because it is a managed and scalable search and analytics engine that supports near real time log ingestion, indexing, and fast querying for troubleshooting and operational dashboards.

OpenSearch provides full text search, aggregations, and visualization through OpenSearch Dashboards and it integrates with ingestion services such as Amazon Kinesis Data Firehose and CloudWatch Logs. These capabilities make OpenSearch well suited to ingest streaming application and system logs and to deliver low latency ad hoc searches and operational dashboards for observability and incident response.

Amazon QuickSight focuses on business intelligence and reporting and it does not provide the log indexing or fast search primitives needed for near real time operational log analysis.

Amazon EMR is designed for batch big data processing with frameworks such as Spark and Hadoop and it is not optimized for low latency interactive searches on streaming logs.

Amazon Athena runs interactive SQL queries over data stored in Amazon S3 and it is not intended for near real time log ingestion and subsecond search and aggregation workflows.

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