> It looks to me like you have work_mem set optimistically large. This
> query seems to be doing *many* large sorts and hashes:
I have work_mem set to 256MB. Reading in PG documentation I now realize that "several sort or hash operations might be running in parallel". So this is most likely the problem, although I don't really understand why memory never seems to increase for any of the other queries (not executed in a transaction). Some of these are at least the size of the query that is giving problems.
Btw, is there some way to determine up front how many sort or hash operations will be running in parallel for a given query?
Regards
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