Re: Something else about Redo Logs disappearing

On Tue, Jun 09, 2020 at 01:27:20AM -0400, Tom Lane wrote:
! Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com> writes:
! > On 6/8/20 7:33 PM, Peter wrote:
! >> That "cp" is usually not synchronous. So there is the possibility
! >> that this command terminates successfully, and reports exitcode zero
! >> back to the Postgres, and then the Postgres will consider that log
! >> being safely away.
!
! > Which is why just following the above command in the docs is:
! > "(This is an example, not a recommendation, and might not work on all
! > platforms.) "
!
! Yeah. There have been discussions about changing that disclaimer to be
! more forceful, because in point of fact a plain "cp" is generally not safe
! enough. You need to fsync the written file, and on many filesystems you
! also have to fsync the directory it's in.

It certainly does not need to be "more forceful" - because this is not
about behavioural education, like training dogs, horses, or monkeys,
and neither do we entertain a BDSM studio.

What it needs instead is mention of the magic word "fsync". Because,
we already know that - we just need a reminder at the proper place.

Systems integrators are professional people. They are not in need of
more beating (spell: forceful education), only of substantial
technical hints and informations.

! > Generally for peace of mind folks use third party tools like:
!
! +1. Rolling your own archive script is seldom advisable.

Well then, using commercial solutions brings it's own problems. E.g.,
the people I happened to work for often had problems with torsion,
which happens when the solution gets longer than, say, twenty meters,
and these are walked at high speeds.

They didn't have a problem with scripting - rather the opposite, they
were happy with it and paid good money for.

cheerio,
PMc