Re: pg_background (and more parallelism infrastructure patches)

>
> Patch 4 adds infrastructure that allows one session to save all of its
> non-default GUC values and another session to reload those values.
> This was written by Amit Khandekar and Noah Misch.  It allows
> pg_background to start up the background worker with the same GUC
> settings that the launching process is using.  I intend this as a
> demonstration of how to synchronize any given piece of state between
> cooperating backends.  For real parallelism, we'll need to synchronize
> snapshots, combo CIDs, transaction state, and so on, in addition to
> GUCs.  But GUCs are ONE of the things that we'll need to synchronize
> in that context, and this patch shows the kind of API we're thinking
> about for these sorts of problems.



> Patch 6 is pg_background itself.  I'm quite pleased with how easily
> this came together.  The existing background worker, dsm, shm_toc, and
> shm_mq infrastructure handles most of the heavily lifting here -
> obviously with some exceptions addressed by the preceding patches.
> Again, this is the kind of set-up that I'm expecting will happen in a
> background worker used for actual parallelism - clearly, more state
> will need to be restored there than here, but nonetheless the general
> flow of the code here is about what I'm imagining, just with somewhat
> more different kinds of state.  Most of the work of writing this patch
> was actually figuring out how to execute the query itself; what I
> ended up with is mostly copied form exec_simple_query, but with some
> difference here and there.  I'm not sure if it would be
> possible/advisable to try to refactor to reduce duplication.