A method for reorganizing a catalog to improve I/O performance includes initially placing a shared lock on a source catalog. The method then makes a point-in-time copy of the source catalog to generate a target catalog. Once the target catalog is generated, the method reorganizes the contents of the target catalog. Optionally, while reorganizing the contents of the target catalog, the method temporarily releases the shared lock on the source catalog and mirrors I/O intended for the source catalog to a buffer. The buffered I/O may then be used to update the target catalog to bring it current with the source catalog. When the target catalog is reorganized and up-to-date, the method upgrades the shared lock on the source catalog to an exclusive lock, overwrites the source catalog with the target catalog, and releases the exclusive lock. A corresponding apparatus and computer program product are also disclosed and claimed herein.