Re: pg_amcheck contrib application

On Thu, Apr 8, 2021 at 5:21 PM Mark Dilger <mark(dot)dilger(at)enterprisedb(dot)com> wrote:
> All this leads me to believe that we should report the following:
>
> 1) If the total number of chunks retrieved differs from the expected number, report how many we expected vs. how many we got
> 2) If the chunk_seq numbers are discontiguous, report each discontiguity.
> 3) If the index scan returned chunks out of chunk_seq order, report that
> 4) If any chunk is not the expected size, report that
>
> So, for your example of chunk 1 missing from chunks [0..17], we'd report that we got one fewer chunks than we expected, that the second chunk seen was discontiguous from the first chunk seen, that the final chunk seen was smaller than expected by M bytes, and that the total size was smaller than we expected by N bytes. The third of those is somewhat misleading, since the final chunk was presumably the right size; we just weren't expecting to hit a partial chunk quite yet. But I don't see how to make that better in the general case.

Hmm, that might be OK. It seems like it's going to be a bit verbose in
simple cases like 1 missing chunk, but on the plus side, it avoids a
mountain of output if the raw size has been overwritten with a
gigantic bogus value. But, how is #2 different from #3? Those sound
like the same thing to me.

--
Robert Haas
EDB: http://www.enterprisedb.com