Re: Is pg_control file crashsafe?

On 03.05.2016 2:17, Tom Lane wrote:

Alex Ignatov <a.ignatov@postgrespro.ru> writes:

I think that rename can help a little bit. At least on some FS it is
atomic operation.

Writing a single sector ought to be atomic too.  I'm very skeptical that
it'll be an improvement to just move the risk from one filesystem
operation to another; especially not to one where there's not even a
terribly portable way to request fsync.

                        regards, tom lane

pg_control is 8k long(i think it is legth of one page in default PG compile settings).
I also think that 8k recording can be atomic. Even if recording of one sector is atomic nobody can say about what sector from 8k record of pg_control  should be written first. It can be last sector or say sector number 10 from 16.