8.1 Performing an Upgrade - Overview

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8 Upgrading an Installation With pg_upgrade : 8.1 Performing an Upgrade - Overview

Place the pg_hba.conf file for both databases in trust authentication mode (to avoid authentication conflicts.
When pg_upgrade starts, it performs a compatibility check to ensure that all required executables are present and contain the expected version numbers. The verification process also checks the old and new $PGDATA directories to ensure that the expected files and subdirectories are in place. If the verification process succeeds, pg_upgrade starts the old postmaster and runs pg_dumpall --schema-only to capture the metadata contained in the old cluster. The script produced by pg_dumpall is used in a later step to recreate all user-defined objects in the new cluster.
Note that the script produced by pg_dumpall recreates only user-defined objects and not system-defined objects. The new cluster will already contain the system-defined objects created by the latest version of Advanced Server.
pg_upgrade runs the pg_dumpall script against the new cluster to create (empty) database objects of the same shape and type as those found in the old cluster. Then, pg_upgrade links or copies each table and index from the old cluster to the new cluster.

8 Upgrading an Installation With pg_upgrade : 8.1 Performing an Upgrade - Overview

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