Re: pg_upgrade: Pass -j down to vacuumdb

On 02/01/2019 20:47, Jesper Pedersen wrote:
> Well, that really depends. The user passed -j to pg_upgrade in order for
> the upgrade to happen faster, so maybe they would expect, as I would,
> that the ANALYZE phase would happen in parallel too.

pg_upgrade -j reduces the *downtime* caused by pg_upgrade during the
upgrade process. Also, during said downtime, nothing else is happening,
so you can use all the resources of the machine.

Once the system is back up, you don't necessarily want to use all the
resources. The analyze script is specifically written to run while
production traffic is active. If you just want to run the analyze as
fast as possible, you can just run vacuumdb -j directly, without using
the script.

Moreover, it's not clear that pg_upgrade and vacuumdb are bound the same
way, so it's not a given that the same -j number should be used.

Perhaps more documentation would be useful here.

--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services