Amit kapila <amit.kap...@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
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