After performing a method 1 upgrade from a 2.2.9 home with standard installation to 2.3, and waiting until the content indexing is listed as 100% complete, searching for any term retrieves no results.

The workaround is simply to update any content, or go to Administration > Content Indexing and selecting Rebuild Search Index.

I have attached two home directories:
1) A home directory for 2.2.9 after performing the standard install. No changes have been made.
2) A home directory for 2.3 created by upgrading the 2.2.9 home directory. No changes have been made. This shows automatic indexing failing.

Steps To Duplicate:

1. Unzip Confluence 2.2.9
2. Set 2.2.9 home directory
3. Start 2.2.9, perform standard installation, stop 2.2.9
4. Unzip Confluence 2.3
5. Set 2.3 home directory to the 2.2.9 home
6. Start 2.3
7. Login, go to Administration > Content Indexing and wait until indexing is listed as 100% complete. My instance states:

• Index Summary Tab -
  Queue Status: Queue is currently idle
  Time Elapsed: 5 minutes, 3 seconds
  Completion: 100% complete
  Finished reindexing 276 objects.

• Queue Contents Tab -
  Queue is currently empty

8. Search for any search term, eg Confluence. No results are found.