Re: Use of 'cp -r' in CREATE DATABASE

I added this comment to the code in case we don't fix cp -r:

/* We might need to use cp -R one day for portability */

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Tom Lane wrote:
> Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
> > IIRC we don't copy anything but plain files and directories - no special
> > files, symlinks or fifos, so the -R/-r differences shouldn't affect us
> > anyway, should they? Also, that should make the implementation of an
> > internal recursive copy much simpler - far fewer cases to consider.
>
> In the ordinary case, yes. There could perhaps be hand-created symlinks
> in the source directory, but I think we would actually prefer that the
> copy be stupid about such things (copy the referenced file rather than
> duplicating the symlink). Special files would be a reason to error out.
>
> Also, I'm not sure that there's any good reason to recurse into
> subdirectories. The only subdirectory a database dir could have at
> present is the temp-file one, and we'd really prefer that that *not* be
> copied at all.
>
> A final point is that implementing CREATE DATABASE via "cp -r" is and
> always has been fundamentally broken anyway, because of the lack of
> interlocking against other backends changing the source database.
> We have a very half-baked defense against that (erroring out if anyone
> else is connected to the source DB at the start of the copy) which
> I would dearly love to get rid of. With a file-by-file copy, it might
> be possible to do better. (I'm wondering if there's any way to take
> ShareLocks on the individual tables we are copying --- if we could
> figure out their OIDs we could do this, but relfilenode is not OID.)
>
> These considerations might change somewhat when we get around to
> implementing tablespaces, but I think it's likely that that will
> make the need for a custom copy implementation greater, not less.
>
> regards, tom lane
>
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