A dump/restore using pg_dump is required for those wishing to migrate data from any previous release.
Observe the following incompatibilities:
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The semantics of the VACUUM command have changed in this release. You may wish to update your maintenance procedures accordingly.
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In this release, comparisons using = NULL will always return false (or NULL, more precisely). Previous releases automatically transformed this syntax to IS NULL. The old behavior can be re-enabled using a postgresql.conf parameter.
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The pg_hba.conf and pg_ident.conf configuration is now only reloaded after receiving a SIGHUP signal, not with each connection.
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The function octet_length() now returns the uncompressed data length.
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The date/time value 'current' is no longer available. You will need to rewrite your applications.
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The timestamp(), time(), and interval() functions are no longer available. Instead of timestamp(), use timestamp 'string' or CAST.
The SELECT ... LIMIT #,# syntax will be removed in the next release. You should change your queries to use separate LIMIT and OFFSET clauses, e.g. LIMIT 10 OFFSET 20.