> ## Documentation index
> Fetch the complete documentation index at: https://dify-docs.docs7.io/llms.txt
> Ask it with GET https://dify-docs.docs7.io/ask?q=<keywords or question>. Short keywords rank best.
> Use these to discover all available pages before exploring further.

# Maintain an Agent Knowledge Base

> Act on the problems the Overview page flags, keep sources syncing, and update documents once a knowledge base is live

Once your apps depend on a knowledge base, check its **Overview** page now and then and fix what it flags.

## Watch the Overview Page

### Needs Attention

- **Source data is stale**: the source has never synced successfully, or its last successful sync was more than 7 days ago. 

    On the **Source** page, click **Sync now**. If the source shows **Error**, fix what it names first, then click **Retry**.

- **Document processing failed**: the latest version of a document couldn't be indexed. If an earlier version was indexed, retrieval keeps serving it until the update goes through. 

    On the **Document** page, hover over the status to see the reason, then click **Retry**. If the reason lies in the content itself, fix it at the source and sync again. For an uploaded file, see [Update Documents](#update-documents).

- **Query quality needs review**: a question asked in a retrieval test or through the Service API came back with weak or no evidence.

    Rerun it on the **Retrieval Test** page, and if it still misses, [make it a bad case](/en/cloud/use-dify/knowledge-base/test-and-tune#bad-cases) to work through.

- **Model configuration is incomplete**: a required model is missing, or the models haven't been validated yet because no document has been indexed. 

    Set any missing model under **Settings** > **Retrieval**. If the knowledge base is still empty, add a document.

### Query Outcomes

To see how often retrieval lets your users down, read the **Query outcomes** chart. It takes every question from the selected period, whether it came from a retrieval test, an app, or an API caller, and sorts it by what retrieval found:

- **No evidence** means nothing came back at all. 

- **Low confidence** means chunks came back, but every one fell below the score threshold. It appears only while **Score Threshold** is on.

- **Answered** is everything else.

When **Low confidence** or **No evidence** climbs, [test and tune retrieval](/en/cloud/use-dify/knowledge-base/test-and-tune) against the questions your users ask.

## Keep Sources Fresh

On the **Source** page, click **Sync now** in a source's menu when you can't wait for its next scheduled run.

To add pages or files to a source, edit it and update its selection.

Removing a source doesn't delete its documents. They stay in the knowledge base but stop refreshing, so delete them separately if you no longer want the content.

## Update Documents

To update an uploaded file, delete the old document and upload the new version. Uploading a file with the same name adds a second document instead of replacing the first.

When content is only temporarily out of date, disable the document instead of deleting it. It leaves retrieval until you enable it again.