With Pg10.0 coming, I have a question about pg_stat_tmp and upgrades that I'm hoping I can get some advice on.
Historically, we've created a tmpfs "disk" and mounted it on $PGDATA/pg_stat_tmp and then started Pg. For
most situations, this works well. However, we have one situation where it doesn't. Therefore, we've decided
to put pg_stat_tmp outside of $PGDATA.
OTOH, it occurs to me that when we run pg_upgrade, we're going to have 2 Pg's running at the same time. So
my concern is that if both new and old have "stats_temp_directory = '/db/pg_stat_tmp'" in their
postgresql.conf, are there going to be conflicts and "bad things" happen? Or is there some sort of
versioning within that area that will keep stuff separate and we'll be OK?
I'm concerned because I don't see anything like versioning when I look in the "dir", so if both of them try
to create a "global.stat" then it seems like "bad things" could happen.
OTOH, it's only stats and only an upgrade, so would it be better to make sure that the new version doesn't
use that (that config isn't set so it uses the dir in PGDATA) and then change it over once the upgrade is
done or what?
I could see where the upgrade process wouldn't do anything with stats while the 2 servers are running (but
only after the upgrade is done) so this might not matter. I will also say that I don't see anything like
this mentioned in the 10.0 docs for pg_upgrade.
I don't think it matters, but we'll be going from 9.5.1 to 10.0.
Thanks,
Kevin
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