Re: [HACKERS] dubious improvement in new psql

Okay, I looked at the code again and I can't see anything wrong
conceptually. It follows libpq semantics which I remember to have grabbed
from the documentation:
results = PQexec(pset->db, query);
/* do something with result */
if (PQstatus(pset->db) == CONNECTION_BAD){    fputs("The connection to the server was lost. Attempting reset: ",
stderr);   PQreset(pset->db);    if (PQstatus(pset->db) == CONNECTION_BAD)    {        fputs("Failed.\n", stderr);
 PQfinish(pset->db);        PQclear(results);        pset->db = NULL;        return false;    }    else
fputs("Succeeded.\n",stderr);}
 


If you can still reproduce this somehow, I'd like to know where it hangs
and/or what the output was.


On 1999-12-25, Tom Lane mentioned:

> The new psql automatically tries to reconnect if the backend disconnects
> unexpectedly.  This feature strikes me as ill-conceived; furthermore
> it appears to be buggy.
> 
> It's ill-conceived because:
> (1) under WAL, following a backend crash the postmaster is going to be
> spending a few seconds reinitializing; an immediate reconnect attempt
> is almost guaranteed to fail.

Then rip out PQreset. It's not psql's job to make these kinds of
decisions.

> (2) if I'm running an SQL script, I think it's extremely foolhardy
> to press on with executing the script as though nothing had happened.
> A backend crash is not an event to be lightly ignored.

Then rip out PQreset. To quote from the docs:

"This function will close the connection to the backend and attempt to
reestablish a new connection to the same postmaster, using all the same
parameters previously used. This may be useful for error recovery if a
working connection is lost."

I don't know all the possible ways a backend can go down, but one of them
might be a short network failure. In that case attempting a reset might be
the reasonable thing to do. Again, this should be addressed at the libpq
level.

> 
> It's buggy because: it doesn't work reliably.  While poking at the
> backend's problems with oversize btree index entries, I saw psql claim
> it had successfully reconnected, and then go into a catatonic state.

Look at the above code; seems like a libpq problem.

> It wouldn't give me a new command prompt (not even with ^C), wouldn't
> exit with ^D, and had to be killed from another shell window.
> 
> This behavior doesn't seem to happen for every crash, but I'm not
> really interested in trying to debug it.  I think the "feature"

I am. :)

> ought to be ripped out.

-- 
Peter Eisentraut                  Sernanders väg 10:115
peter_e@gmx.net                   75262 Uppsala
http://yi.org/peter-e/            Sweden