On 25 March 2017 at 13:10, Tomas Vondra <tomas.von...@2ndquadrant.com> wrote: > while working on a patch I ran into some crashes that seem to be caused by > inconsistent handling of max_parallel_workers - queries still seem to be > planned with parallel plans enabled, but then crash at execution. > > The attached script reproduces the issue on a simple query, causing crashed > in GatherMerge, but I assume the issue is more general.
I had a look at this and found a bunch of off by 1 errors in the code. I've attached a couple of patches, one is the minimal fix, and one more complete one. In the more complete one I ended up ditching the GatherMergeState->nreaders altogether. It was always the same as nworkers_launched anyway, so I saw no point in it. Here I've attempted to make the code a bit more understandable, to prevent further confusion about how many elements are in each array. Probably there's more that can be done here. I see GatherState has nreaders too, but I've not looked into the detail of if it suffers from the same weirdness of nreaders always matching nworkers_launched. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
gather_merge_minimal_fix.patch
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gather_merge_fix.patch
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