BTW, while nosing around looking for an explanation for our cross-version-upgrade woes, I chanced to notice that relation_statistics_update rejects negative values for relpages and relallvisible. This is nonsense. Internally those values are BlockNumbers and can have any value from 0 to UINT32_MAX. We represent them as signed int32 at the SQL level, which means they can read out as any int32 value. So the range checks that are being applied to them are flat wrong and should be removed. Admittedly, you'd need a table exceeding 16TB (if I did the math right) to see a problem, but that doesn't make it not wrong.
It might be a good idea to change the code so that it declares these values internally as BlockNumber and uses PG_GETARG_UINT32, but I think that would only be a cosmetic change not a correctness issue. regards, tom lane