If you enter the for proxy_update clause with no other options, alter database does not extend the size of the database; instead, the proxy tables, if any, are dropped from the proxy database and re-created from the metadata obtained from the path name specified during create database ... with default_location = ‘pathname’.
If you use alter database with other options to extend the size of the database, the proxy table synchronization is performed after the size extensions are made.
for proxy_update provides the database administrator with an easy-to-use, single-step operation with which to obtain an accurate and up-to-date proxy representation of all tables at a single remote site.
Resynchronization is supported for all external data sources, not just the primary server in a high availability-cluster environment. Also, a database need not have been created with the for proxy_update clause. If a default storage location has been specified, either through create database or with sp_defaultloc, the metadata contained within the database can be synchronized with the metadata at the remote storage location.
To make sure databases are synchronized correctly so that all the proxy tables have the correct schema to the content of the primary database you just reloaded, you may need to run the for proxy_update clause on the server hosting the proxy database.