Re: psql - add SHOW_ALL_RESULTS option

On 23.12.21 12:40, Fabien COELHO wrote:
>> In [0], it was reported that certain replication commands result in 
>> infinite loops because of faulty error handling.  This still happens.  
>> I wrote a test for it, attached here.  (I threw in a few more basic 
>> tests, just to have some more coverage that was lacking, and to have a 
>> file to put the new test in.)
> 
> Hmmm… For some unclear reason on errors on a PGRES_COPY_* state 
> PQgetResult keeps on returning an empty result. PQexec manually ignores 
> it, so I did the same with a comment, but for me the real bug is somehow 
> in PQgetResult behavior…
> 
>> In [1], it was reported that server crashes produce duplicate error 
>> messages. This also still happens.  I didn't write a test for it, 
>> maybe you have an idea.  (Obviously, we could check whether the error 
>> message is literally there twice in the output, but that doesn't seem 
>> very general.)  But it's easy to test manually: just have psql 
>> connect, shut down the server, then run a query.
> 
> This is also a feature/bug of libpq which happens to be hidden by 
> PQexec: when one command crashes PQgetResult actually returns *2* 
> results. First one with the FATAL message, second one when libpq figures 
> out that the connection was lost with the second message appended to the 
> first. PQexec just happen to silently ignore the first result. I added a 
> manual reset of the error message when first shown so that it is not 
> shown twice. It is unclear to me whether the reset should be somewhere 
> in libpq instead. I added a voluntary crash at the end of the psql test.

I agree that these two behaviors in libpq are dubious, especially the 
second one.  I want to spend some time analyzing this more and see if 
fixes in libpq might be appropriate.