Re: [patch] pg_copy - a command for reliable WAL archiving

On 2014-08-19 17:42:06 -0400, Alvaro Herrera wrote:
> MauMau wrote:
>
> > With that said, copying to a temporary file like <dest>.tmp and
> > renaming it to <dest> sounds worthwhile even as a basic copy
> > utility. I want to avoid copying to a temporary file with a fixed
> > name like _copy.tmp, because some advanced utility may want to run
> > multiple instances of pg_copy to copy several files into the same
> > directory simultaneously. However, I'm afraid multiple <dest>.tmp
> > files might continue to occupy disk space after canceling copy or
> > power failure in some use cases, where the copy of the same file
> > won't be retried. That's also the reason why I chose to not use a
> > temporary file like cp/copy.
>
> Is there a way to create a link to a file which only exists as an open
> file descriptor? If there was, you could create a temp file, open an
> fd, then delete the file. That would remove the issue with files being
> leaked due to failures of various kinds.

Isn't this a solution looking for a problem? We're using tempfiles in
dozens of other places and I really don't see why this is the place to
stop doing so. Just copy to <dest>.tmp and move it into place. If things
crash during that, the command will be repeated shortly afterwards again
*anyway*. Let's not get into platform specific games here.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services