Re: WIP parallel restore patch

Andrew Dunstan wrote:
> 
> Attached is my latest parallel restore patch. I think it's functionally
> complete for Unix.
> 
> Many bugs have been fixed since the last patch, and the hardcoded
> limitation to two table dependencies is removed. It seems fairly robust
> in my recent testing.
> 
> Remaining to be done:
> 
> . code cleanup
> . better error checking in a few places
> . final decision re command line option names/defaults
> . documentation
> . Windows support.

I've looked around this a bit, and it's fairly clear where the issue
comes in with Windows - we get heap corruption. Most likely because we
have multiple threads working on the same data somewhere.

I notice for example that we're doing a shallow copy of the
ArchiveHandle with a simple memcpy() for each thread. But that struct
contains a number of things like file descriptors and pointers. Have you
verified for each and every one of those that it actually doesn't get
modified anywhere? If not, a deep copy may be needed to make sure of that.

Other than that, are there any global variables that may be addressed
from more than one worker? If so they need to be marked as TLS.

And yes, I got hit by the lack of error checking a couple of times
during my testing - it would probably be a good idea to add that as soon
as possible, it helps a lot with the debugging.

If I run it with just a single thread, it also crashes in PQfinish()
called from die_horribly(), when trying to free conn->pgpass, which has
a value (non-NULL) but is not a valid pointer. This crash happens in the
worker thread, after it has logged that "fseek is required" - that's an
indicator something being passed down to the thread is either wrong or
being scribbled upon after the fact.

I didn't dig into these questions specifically - since you have already
been reading up on this code to do the patch you can probably reach the
answer to them much quicker :-) So I'll stick to the questions.

//Magnus