Date: Tue, 10 Jun 2014 10:13:39 -0700 (PDT)
From: David G Johnston <david.g.johnston@gmail.com>
To: pgsql-hackers@postgresql.org
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Subject: Re: /proc/self/oom_adj is deprecated in newer Linux kernels
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Gurjeet Singh-4 wrote
> Even if the clueless DBA tries to set the oom_score_adj below that of
> Postmaster, Linux kernel prevents that from being done. I demonstrate
> that in the below screen share. I used GUC as well as plain command
> line to try and set a child's badness (oom_score_adj) to be lower than
> that of Postmaster's, and Linux disallows doing that, unless I use
> root's powers.
> 
> So the argument that this GUC is a security concern, can be ignored.
> Root user (one with control of start script) still controls the lowest
> badness setting of all Postgres processes. If done at fork_process
> time, the child process simply inherits parent's badness setting.

The counter point here is that the postmaster can be set to "no kill" and
the >= condition allows for children to achieve the same while it is our
explicit intent that the children be strictly > parent.

To that end, should the adjustment value be provided as an offset to the
postmasters instead of an absolute value - and disallow <= zero offset
values in the process?

I get and generally agree with the environment variable proposal and it's
stated goal to restrict whom can makes changes. But how much less cost does
an environment variable have than a GUC if one GUC argument is still its
maintenance overhead?

David J.


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