1. A method for managing a deduplication database in a deduplication storage system, wherein the deduplication database stores database entries comprising deduplication signatures corresponding to deduplication data blocks stored in secondary storage, the method comprising: by a secondary storage computing device comprising computer hardware, determining whether a working copy of a first database entry of a plurality of database entries of a deduplication database exists in a local database residing in main memory of the secondary storage computing device, wherein the deduplication database resides in one or more storage devices external to the secondary storage computing device; based at least on a determination that the working copy of the first database entry does not reside in the local database, querying the deduplication database for the first database entry and generating the working copy of the first database entry based at least on information received from the deduplication database in response to the querying; modifying the working copy of the first database entry based on a storage operation involving a stored deduplication data block corresponding to the first database entry; detecting a triggering condition indicating that a plurality of working copies corresponding to a respective plurality of database entries in the deduplication database should be merged with the deduplication database, the plurality of working copies including the working copy of the first database entry contained in the local database; and based at least on said detecting the triggering condition, updating the deduplication database by merging at least some contents of the plurality of working copies with the deduplication database.