On Wed, Mar 25, 2020 at 3:19 PM Andres Freund <and...@anarazel.de> wrote: > > Hi, > > On 2019-09-18 13:51:00 -0400, James Coleman wrote: > > In my experience it's not immediately obvious (even after reading the > > documentation) the implications of how concurrent index builds manage > > transactions with respect to multiple concurrent index builds in > > flight at the same time. > > > > Specifically, as I understand multiple concurrent index builds running > > at the same time will all return at the same time as the longest > > running one. > > > > I've attached a small patch to call this caveat out specifically in > > the documentation. I think the description in the patch is accurate, > > but please let me know if there's some intricacies around how the > > various stages might change the results. > > > > James Coleman > > I'd much rather see effort spent fixing this issue as far as it relates > to concurrent CICs. For the snapshot waits we can add a procarray flag > (alongside PROCARRAY_VACUUM_FLAG) indicating that the backend is > doing. Which WaitForOlderSnapshots() can then use to ignore those CICs, > which is safe, because those transactions definitely don't insert into > relations targeted by CIC. The change to WaitForOlderSnapshots() would > just be to pass the new flag to GetCurrentVirtualXIDs, I think.
Alvaro: I think you had some ideas on this too; any chance you've know of a patch that anyone's got cooking? Andres: If we got this fixed in current PG would you be opposed to documenting the caveat in previous versions? Thanks, James
