Re: Server won't start with fallback setting by initdb.

On Wed, Mar 7, 2018 at 6:43 PM, Michael Paquier <michael@paquier.xyz> wrote:
> On Wed, Mar 07, 2018 at 06:39:32PM -0500, Tom Lane wrote:
>> OK, seems like I'm on the short end of that vote.  I propose to push the
>> GUC-crosschecking patch I posted yesterday, but not the default-value
>> change, and instead push Kyotaro-san's initdb change.  Should we back-patch
>> these things to v10 where the problem appeared?
>
> I would vote for a backpatch.  If anybody happens to run initdb on v10
> and gets max_connections to 10, that would immediately cause a failure.
> We could also wait for sombody to actually complain about that, but a
> bit of prevention does not hurt to ease future user experience on this
> released version.

In theory, back-patching the GUC-crosschecking patch could cause the
cluster to fail to restart after the upgrade.  It's pretty unlikely.
We have to postulate someone with, say, default values but for
max_connections=12.  But it's not impossible.  I would be inclined to
back-patch the increase in the max_connections fallback from 10 to 20
because that fixes a real, if unlikely, failure mode, but treat the
GUC cross-checking stuff as a master-only improvement.  Although it's
unlikely to hurt many people, there's no real upside.  Nobody is going
to say "boy, it's a good thing they tidied that GUC cross-checking in
the latest major release -- that really saved my bacon!".  Nothing is
really broken as things stand.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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