why does the transaction age of template0 DB increase in postgresql

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why does the transaction age of template0 DB increase while it is never been used?

   datname        |    age    | 
 ----------------------+-----------+
  template0            | 192232070
enterprisedb postgresql-11 postgresql-12 postgresql
1 Answers

Every database has a datfrozenxid in its pg_database entry. This is identical to the minimum relfrozenxid of the pg_class entries of all tables in the database.

Whenever VACUUM freezes tuples in a table, it can advance these columns.

There is no real need to vacuum template0 regularly. However, even in that database a table receives an anti-wraparound autovacuum run whenever its relfrozenxid becomes older than autovacuum_freeze_max_age. This will be done very quickly: PostgreSQL will see in the visibility map that all pages are “all frozen” and advance relfrozenxid.

This is no real problem, so nobody sees a need to change or optimize that.

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