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When invoking pg_upgrade, you can use a command-line option to specify whether pg_upgrade should copy or link each table and index in the old cluster to the new cluster.
If you choose to copy data from the old cluster to the new cluster, pg_upgrade will still reduce the amount of time required to perform an upgrade compared to the traditional dump/restore procedure. pg_upgrade uses a file-at-a-time mechanism to copy data files from the old cluster to the new cluster (versus the row-by-row mechanism used by dump/restore). When you use pg_upgrade, you avoid building indexes in the new cluster; each index is simply copied from the old cluster to the new cluster. Finally, using a dump/restore procedure to upgrade requires a great deal of workspace to hold the intermediate text-based dump of all of your data, while pg_upgrade requires very little extra workspace.


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