Is incremental indexing supported by the connector?
Yes. This is done using a snapshot file which is created when doing a full crawl. It saves the state of every crawled item and on the next incremental crawl it’ll use this file to compare and get any adds, updates or deletes. A new snapshot file is created after an incremental crawl to save the changes done.
Why do I need to set up permissions at Web Application level?
Those permissions ("Full Read") are required so the connector can fetch additional information from site collections. This information is required for incremental indexing.
If setting permissions at Web Application level is not suitable to your environment, consider setting site collection administrator rights to the crawler account on each site collection you want to crawl. (This will work without Web App permissions, but has to be set on every site collection.)
Why is the connector crawling the whole site collection? Even if the start URL is from a sub-site?
This usually happens when you are trying to access your site using an IP address instead of hostname. The traffic is redirected to the top level site by IIS or a router, so the connector receives the wrong information from SharePoint. To fix, simply use the hostname of your SharePoint front end.
Why is does an incremental crawl last as long as a full crawl?
In Aspire 2.0 and 2.0.1, the Sharepoint 2010 Connector performs incremental crawls based on snapshot files, which are meant to match the exact documents that have been indexed by the connector to the search engine. On an incremental crawl, the connector fully crawls the Sharepoint content the same way as a full crawl, but it only indexes the modified, new or deleted documents during that crawl.
For a discussion on crawling, see here.
The connector fails with 401 unauthorized and this stack trace:
Check prerequisites section for more details.
The connectors keeps failing with 401 unauthorized, even when the user has enough permissions.
Make sure the user has enough permissions. You can use the 'Check Permissions' option on the SharePoint site that you want to crawl.