Why are documents added to a knowledge base not searchable even though their document status is reported as INDEXED?

The behavior you're experiencing is likely due to the distributed nature of OpenSearch and its indexing process, rather than an inaccuracy in the GetKnowledgeBaseDocuments API. When documents are added to a Bedrock Knowledge Base and reported as INDEXED, they have been successfully processed and stored, but may not be immediately searchable in OpenSearch.

This delay is caused by OpenSearch's indexing and search architecture. When data is ingested, it goes through several stages:

1. Documents are received and processed by indexing compute units.
2. The indexed data is then stored in Amazon S3.
3. The search index is updated to make the documents searchable.

There's a slight lag between when documents are indexed and when they become fully searchable. This is because OpenSearch uses a query-then-fetch approach for searching distributed data. The index updates need to propagate across all shards and become consistent before the documents are fully searchable.

To determine when documents are fully processed and searchable, you have a few options:

1. Implement a retry mechanism with exponential backoff for your RetrieveAndGenerate queries. This approach allows time for the index to become consistent.

2. Monitor OpenSearch Serverless metrics using Amazon CloudWatch. Specifically, you can track the "SearchableDocuments" metric, which represents the total number of searchable documents in a collection or index. When this metric stabilizes after an ingestion job, it's a good indicator that the documents are searchable.

3. Use the OpenSearch Serverless API to perform test queries periodically after ingestion. When your test queries return the expected results, you can consider the documents fully searchable.

4. Check the ingestion job statistics using the AWS CLI command "aws bedrock-agent list-ingestion-jobs". This will give you detailed information about the number of documents scanned, indexed, and any failures.

Remember that while GetKnowledgeBaseDocuments accurately reports the processing status, there's an inherent delay in making documents fully searchable due to the distributed nature of OpenSearch. This delay is normal and should be accounted for in your application's design.

Sources
How is the indexing process taken care of in opensearch serverless? | AWS re:Post
Community | Troubleshooting the ML Commons Framework
Knowledge Base for Bedrock Indexing | AWS re:Post
Monitoring OpenSearch Serverless with Amazon CloudWatch - Amazon OpenSearch Service