Re: Proposal for Allow postgresql.conf values to be changed via SQL

Amit kapila <amit.kapila@huawei.com> writes:
> On Friday, November 23, 2012 10:10 PM Fujii Masao wrote:
>> What happens if the server crashes while SET PERSISTENT is writing the
>> setting to the file? A partial write occurs and restart of the server would fail
>> because of corrupted postgresql.auto.conf?

> This situation will not happen as SET PERSISTENT command will first write to ".lock" file and then at commit time, 
> rename it to ".auto.conf".

Yes, the right way to write the config file is to write under a
temporary name, fsync the file, and then use rename(2) to atomically
move it into place.  However, the above is contemplating some extra
complexity that I think is useless and undesirable, namely postponing
the rename until commit time.  The point of the suggestion that SET
PERSISTENT not be allowed inside a transaction block is so that you can
write the file immediately rather than have to add commit-time mechanism
to support the feature.  Aside from being extra complexity, and some
extra cycles added in *every single commit*, a post-commit write creates
another way to have post-commit failures, which we cannot cope with in
any sane way.
        regards, tom lane