On Thu, Mar 19, 2015 at 11:13 AM, Robert Haas <robertmh...@gmail.com> wrote: > Here is yet another version of this patch. In addition to the fixes > mentioned above, this version includes some minor rebasing around > recent commits, and also better handling of the case where we discover > that we cannot launch workers after all. This can happen because (1) > dynamic_shared_memory_type=none, (2) the maximum number of DSM > segments supported by the system configuration are already in use, or > (3) the user creates a parallel context with nworkers=0. In any of > those cases, the system will now create a backend-private memory > segment instead of a dynamic shared memory segment, and will skip > steps that don't need to be done in that case. This is obviously an > undesirable scenario. If we choose a parallel sequential scan, we > want it to launch workers and really run in parallel. Hopefully, in > case (1) or case (3), we will avoid choosing a parallel plan in the > first place, but case (2) is pretty hard to avoid completely, as we > have no idea what other processes may or may not be doing with dynamic > shared memory segments ... and, in any case, degrading to non-parallel > execution beats failing outright.
I see that you're using git format-patch to generate this. But the patch is only patch 1/4. Is that intentional? Where are the other pieces? I think that the parallel seqscan patch, and the assessing parallel safety patch are intended to fit together with this patch, but I can't find a place where there is a high level overview explaining just how they fit together (I notice Amit's patch has an "#include "access/parallel.h", which is here, but that wasn't trivial to figure out). I haven't been paying too much attention to this patch series. -- Peter Geoghegan -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
