Re: Misdesigned command/status APIs for parallel dump/restore

I wrote:
> I am pretty strongly tempted to get rid of MasterStartParallelItem
> altogether and just hard-code what it does in DispatchJobForTocEntry.
> ...
> A different line of thought would be to fix the worker-command-parsing
> situation by allowing the parsing to happen in format-specific code,
> but avoid duplicative coding by letting archive formats share a common
> implementation function if they had no need for any custom data.

In the attached patch for this, I took a middle ground of separating out
the command and status string building and parsing functions. There isn't
presently any provision for letting archive format modules override these,
but that could easily be added if we ever need it. Meanwhile, this saves
about 100 lines of rather messy code.

Like the other couple of patches I've posted recently for parallel dump,
this is against current HEAD. There will be minor merge conflicts when
these patches are combined; but they should be reviewable independently,
so I'll worry about the merge issues later.

regards, tom lane