RE: pg_upgrade: Pass -j down to vacuumdb

Hi,

According to CF app, this patch needs review so I took a look at it.
Currently, your patch applies and builds cleanly, and all tests are also successful
based from the CF bot patch tester.

I'm not sure if I have understood the argument raised by Peter correctly. 
Quoting Peter, "it's not clear that pg_upgrade and vacuumdb are bound the same way, so it's not a given that the same
-jnumber should be used."
 
I think it's whether the # jobs for pg_upgrade is used the same way for parallel vacuum. 

According to the official docs, the recommended setting for pg_upgrade --j option is the maximum of the number of CPU
coresand tablespaces. [1]
 
As for vacuumdb, parallel vacuum's (-j) recommended setting is based from your max_connections [2], which is the max #
ofconcurrent connections to your db server.
 

[1] https://www.postgresql.org/docs/current/pgupgrade.html
[2] https://www.postgresql.org/docs/current/app-vacuumdb.html


Regards,
Kirk Jamison