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Re: Proposal "stack trace" like debugging option in PostgreSQL

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Hello

On 08/01/2016 12:15 AM, Tom Lane wrote:
Edson Richter <edsonrichter@xxxxxxxxxxx> writes:
From: tgl@xxxxxxxxxxxxx
Uh, doesn't the CONTEXT field of error messages give you that already?

Would you give me an example where I can get the info you mention above? Do I need to enable some kind of parameter to get this context field?

Well, you have not mentioned what sort of client environment you are
using, but the server certainly sends that information.  In psql,
for example, I can do this:

regression=# create table foo (f1 int primary key, f2 text);
CREATE TABLE
regression=# create function ifoo(int, text) returns void as
$$ begin insert into foo values($1,$2); end $$ language plpgsql;
CREATE FUNCTION
regression=# create function ifoo2(int, text) returns void as
$$ begin perform ifoo($1,$2); end $$ language plpgsql;
CREATE FUNCTION
regression=# select ifoo2(1,'foo');
 ifoo2
-------

(1 row)

regression=# select ifoo2(1,'foo');
ERROR:  duplicate key value violates unique constraint "foo_pkey"
DETAIL:  Key (f1)=(1) already exists.
CONTEXT:  SQL statement "insert into foo values($1,$2)"
PL/pgSQL function ifoo(integer,text) line 1 at SQL statement
SQL statement "SELECT ifoo($1,$2)"
PL/pgSQL function ifoo2(integer,text) line 1 at PERFORM

If you're using a misdesigned client that will not show these auxiliary
error fields, you could try looking in the server log --- at default
log verbosity, it will contain that info too.  The above test case
gave me this log entry:

ERROR:  duplicate key value violates unique constraint "foo_pkey"
DETAIL:  Key (f1)=(1) already exists.
CONTEXT:  SQL statement "insert into foo values($1,$2)"
        PL/pgSQL function ifoo(integer,text) line 1 at SQL statement
        SQL statement "SELECT ifoo($1,$2)"
        PL/pgSQL function ifoo2(integer,text) line 1 at PERFORM
STATEMENT:  select ifoo2(1,'foo');

			regards, tom lane



Maybe this could help, too.

In the documentation there is a description of how to get the call stack of functions:

https://www.postgresql.org/docs/current/static/plpgsql-control-structures.html

40.6.7. Obtaining Current Execution Information

The GET [ CURRENT ] DIAGNOSTICS command retrieves information about current execution state (whereas the GET STACKED DIAGNOSTICS command discussed above reports information about the execution state as of a previous error). This command has the form:

GET [ CURRENT ] DIAGNOSTICS variable { = | := } item [ , ... ];

Currently only one information item is supported. Status item PG_CONTEXT will return a text string with line(s) of text describing the call stack. The first line refers to the current function and currently executing GET DIAGNOSTICS command. The second and any subsequent lines refer to calling functions further up the call stack. For example:

CREATE OR REPLACE FUNCTION outer_func() RETURNS integer AS $$
BEGIN
  RETURN inner_func();
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION inner_func() RETURNS integer AS $$
DECLARE
  stack text;
BEGIN
  GET DIAGNOSTICS stack = PG_CONTEXT;
  RAISE NOTICE E'--- Call Stack ---\n%', stack;
  RETURN 1;
END;
$$ LANGUAGE plpgsql;

SELECT outer_func();

NOTICE:  --- Call Stack ---
PL/pgSQL function inner_func() line 5 at GET DIAGNOSTICS
PL/pgSQL function outer_func() line 3 at RETURN
CONTEXT:  PL/pgSQL function outer_func() line 3 at RETURN
 outer_func
 ------------
           1
(1 row)

Regards
Charles

--
Swiss PostgreSQL Users Group
c/o Charles Clavadetscher
Treasurer
Motorenstrasse 18
CH – 8005 Zürich

http://www.swisspug.org

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