Re: PL/pgSQL, RAISE and error context - Mailing list pgsql-hackers

On 07/07/2015 04:56 PM, Merlin Moncure wrote:
> On Tue, Jul 7, 2015 at 8:13 AM, Heikki Linnakangas <hlinnaka@iki.fi> wrote:
>> On 01/26/2015 05:14 PM, Tom Lane wrote:
>>>
>>> Pavel Stehule <pavel.stehule@gmail.com> writes:
>>>>
>>>> 2015-01-26 14:02 GMT+01:00 Marko Tiikkaja <marko@joh.to>:
>>>> I am thinking, so solution
>>>
>>>
>>>>        /* if we are doing RAISE, don't report its location */
>>>>       if (estate->err_text == raise_skip_msg)
>>>>           return;
>>>
>>>
>>>> is too simple, and this part should be fixed. This change can be done by
>>>> on
>>>> plpgsql or libpq side. This is bug, and it should be fixed.
>>>
>>>
>>> Doing this in libpq is utterly insane.  It has not got sufficient context
>>> to do anything intelligent.  The fact that it's not intelligent is exposed
>>> by the regression test changes that the proposed patch causes, most of
>>> which do not look like improvements.
>>
>> How can the server know if the client wants to display context information?
>
> It doesn't have to if the behavior is guarded with a GUC.  I just
> don't understand what all the fuss is about.  The default behavior of
> logging that is well established by other languages (for example java)
> that manage error stack for you should be to:
>
> *) Give stack trace when an uncaught exception is thrown
> *) Do not give stack trace in all other logging cases unless asked for

Java's exception handling is so different from PostgreSQL's errors that 
I don't think there's much to be learned from that. But I'll bite:

First of all, Java's exceptions always contain a stack trace. It's up to 
you when you catch an exception to decide whether to print it or not. 
"try { ... } catch (Exception e) { e.printStackTrace() }" is fairly 
common, actually. There is nothing like a NOTICE in Java, i.e. an 
exception that's thrown but doesn't affect the control flow. The best I 
can think of is System.out.println(), which of course has no stack trace 
attached to it.

Perhaps you're arguing that NOTICE is more like printing to stderr, and 
should never contain any context information. I don't think that would 
be an improvement. It's very handy to have the context information 
available if don't know where a NOTICE is coming from, even if in most 
cases you're not interested in it.

This is really quite different from a programming language's exception 
handling. First, there's a server, which produces the errors, and a 
separate client, which displays them. You cannot catch an exception in 
the client.

BTW, let me throw in one use case to consider. We've been talking about 
psql, and what to print, but imagine a more sophisticated client like 
pgAdmin. It's not limited to either printing the context or not. It 
could e.g. hide the context information of all messages when they occur, 
but if you double-click on it, it's expanded to show all the context, 
location and all. You can't do that if the server doesn't send the 
context information in the first place.

> I would be happy to show you the psql redirected output logs from my
> nightly server processes that spew into the megabytes because of
> logging various high level steps (did this, did that).

Oh, I believe you. I understand what the problem is, we're only talking 
about how best to address it.
- Heikki