Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> writes:
> So you have 16GB of RAM and here we're failing to posix_fallocate()
> 50MB (actually we can't tell if it's the ftruncate() or
> posix_fallocate() call that failed, but the latter seems more likely
> since the former just creates a big hole in the underlying tmpfs
> file). Can you share the query plan (EXPLAIN SELECT ...)?
I wonder if OP is running with a tmpfs size setting that's less than
the traditional Linux default of half of physical RAM size.
regards, tom lane