ERROR: Transaction not found - postgresql

Question

I have just found in pg_log some line of this specific error:
ERROR: Transaction not found //some_hash
error + surrounding lines:
2014-06-04 15:08:49 CEST my_user db_name LOCATION: exec_bind_message, postgres.c:1771
2014-06-04 15:08:49 CEST my_user db_name NOTICE: 00000: Transaction expired
2014-06-04 15:08:49 CEST my_user db_name LOCATION: exec_stmt_raise, pl_exec.c:3041
2014-06-04 15:08:49 CEST my_user db_name ERROR: P0001: Transaction not found egcrppnddxt82frc
2014-06-04 15:08:49 CEST my_user db_name LOCATION: exec_stmt_raise, pl_exec.c:3041
I have found this error only in postgres source code. Is it some internal error? When it can occur?
PostgreSQL version:
PostgreSQL 9.3.2 on x86_64-unknown-linux-gnu,
compiled by gcc (Debian 4.4.5-8) 4.4.5, 64-bit
It's a comment I have found in the source code:
/* We check the transaction's database ID for paranoia's sake: if
it's in another DB then its xmin does not cover us. Caller
should have detected this already, so we just treat any funny
cases as "transaction not found".*/

Answer 1

Your errors are being thrown by user defined code written in PL/PgSQL.
They are not coming from PostgreSQL. That is why the message Transaction not found does not appear in PostgreSQL's source code except in comments. You're barking up entirely the wrong tree.
This:
2014-06-04 15:08:49 CEST my_user db_name ERROR: P0001: Transaction not found egcrppnddxt82frc
2014-06-04 15:08:49 CEST my_user db_name LOCATION: exec_stmt_raise, pl_exec.c:3041
shows:
The SQLSTATE is P0001, the default code used by RAISE ERROR in PL/PgSQL if you don't override it;
It's being logged from exec_stmt_raise, the RAISE statement, inside pl_exec.c, the PL/PgSQL executor;
Transaction not found egcrppnddxt82frc is a message from your application
I would've expected to see more context lines showing the PL/PgSQL procedure name, too, but perhaps in an explicit RAISE they're only emitted to the client, not the server error log. I don't remember.
You might be able to locate the culprit with:
\x
SELECT *
FROM pg_proc p
INNER JOIN pg_language l ON (p.prolang = l.oid)
WHERE l.lanname = 'plpgsql'
AND p.prosrc LIKE '%Transaction not found%';
.. assuming that the procedure isn't forming the error from several separate strings or getting it from somewhere else.
This is why you always include complete, un-edited error messages. If you'd just showed the whole error line I could've told you what was going on hours ago.