preventing transaction wraparound

[Mike Broers <mbroers@xxxxxxxxx>]

Lately I have been paranoid about the possibility of transaction wrap around failure due to a potential orphaned toast table.  I have yet to prove that I have such an object in my database.. but I am running Postgres 8.3 with auto_vacuum enabled and am doing nightly manual vacuums as well and cannot explain the results of this query.  Any assistance is greatly appreciated.

Yesterday I ran:

production=# select datname, age(datfrozenxid) from pg_database;

  datname   |    age    

------------+-----------

 template1  | 100260769

 template0  |  35997820

 postgres   | 100319291

 stage      | 100263734

 production | 100319291

and today after the nightly vacuum ran I got this:

production=# select datname, age(datfrozenxid) from pg_database;
 datname   |    age    
------------+-----------
template1  | 100677381
template0  |  37594611
postgres   | 100738854
stage      | 100680248
production | 100738770

Am I just counting down to 2,000,000,000 and the postgresapocolypse? Is there a way for me to determine what the actual transaction threshold is going to be? I've read the postgresql docs and greg smiths section in high performance and have to admit i am having difficulty understanding how this number is not retreating after a database manual vacuum.

thanks,

Mike