What to watch out for when ALTERing NUMERIC(38,0) to BIGINT?

[Ron <ronljohnsonjr@xxxxxxxxx>]

    AWS RDS Postgresql 12.10
    
    
    We've got tables with columns of data type NUMERIC(38,0) which are a
    legacy from an Oracle migration.
    
    Besides what's mentioned in
    https://www.postgresql.org/docs/12/ddl-alter.html#id-1.5.4.8.10,
    what happens internally when I run:
    ALTER TABLE foo ALTER COLUMN bar TYPE BIGINT;
    
    I'm thinking mostly of record fragmentation.

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