address book freeze on merge duplicates

I was also having the same problem (frozen app, right pane unresponsive to selections in the left pane, unable to search) but trashing the database in Library > Application Support > AddressBook did not work for me, so I called Apple Support. They asked if I was syncing with iCloud (yes, I was) and had me 1) export the address book database as a backup (File > Export > Address Book Archive), then 2) open System Preferences > iCloud, then uncheck the Contacts (a dialogue box will appear - click on delete) and leave it unchecked for 15-20 seconds, then recheck the contacts and wait about 30 seconds (for the db to repopulate). Now my AB is happy! Hope this works for you. PB

Had the same problem in Mavericks.

In my case, I'm syncing with iCloud and Exchange.

Repeated the steps from Peter Black2. Problem solved! (Dups gone too)

This worked for me. Thanks!

Perfect!! Thanks so much!! no more duplicate issues and no more freezing!