Обсуждение: cursor "" does not exist

Hi,

I'm querying a Postgres 8.0.3 database from Java via the 8.0-311 JDBC 
driver. It mostly works. I ran into the "cursor does not exist" problem, 
but was able to fix it with
connection.setAutoCommit(false);

Or so I thought.

There are several JSP pages which still throw the 'cursor "<unnamed 
portal 1>" does not exist' error. Everything works well if I call the 
same Java fuction on the command line.

I tried to observe the network packets and found an interesting thing: 
the "select *" queries and responses that works look like this:

Request S_1 BEGIN  select * from user_pkg.GetPerson_fcn($1) as result 571
Response BEGIN result <unnamed portal 1>C SELECT

While those that fail look like this:

Request select * from material_pkg.ListCautions_fcn($1,$2)  as result B
Response result <unnamed portal 1>C SELECT

Note that the successful ones contain strings "S_1" and "BEGIN", and the 
failed ones do not. However, there also are successful queries without 
these strings, but they are not "select *" queries. Eg,

Request SELECT typname FROM pg_catalog.pg_type WHERE oid=$1 1790
Response typname refcursorC SELECT

When I do it successfully on the command line, the "S_1" and "BEGIN" 
lines are also present in the query.

I have a feeling it's some idiosyncrasy that I'm not familiar with. Does 
"BEGIN" refer to the beginning of a trasaction?

I will be grateful for any suggestions.

Simon
-- 

Simon (Vsevolod ILyushchenko)   simonf@cshl.edu            http://www.simonf.com

Terrorism is a tactic and so to declare war on terrorism
is equivalent to Roosevelt's declaring war on blitzkrieg.

Zbigniew Brzezinski, U.S. national security advisor, 1977-81

On Wed, Jun 15, 2005 at 06:45:56PM -0400, Vsevolod (Simon) Ilyushchenko wrote:
> While those that fail look like this:
> 
> Request select * from material_pkg.ListCautions_fcn($1,$2)  as result B
> Response result <unnamed portal 1>C SELECT
> 
> Note that the successful ones contain strings "S_1" and "BEGIN", and the 
> failed ones do not. However, there also are successful queries without 
> these strings, but they are not "select *" queries. Eg,

> I have a feeling it's some idiosyncrasy that I'm not familiar with. Does 
> "BEGIN" refer to the beginning of a trasaction?

Yes.  A transaction looks like this:

BEGIN;
SQL1;
SQL2;
COMMIT;

But it also looks like this:

SQL3;

because in PostgreSQL, everything is always automatically in a
transaction, and a bald SQL statement is just a transaction one
statement long.  With autocommit off, I think what you get is no
COMMIT, but you still get the bald transaction.

What you really need is to make sure you're starting a
multi-statement transaction every time.

A

-- 
Andrew Sullivan  | ajs@crankycanuck.ca
The plural of anecdote is not data.    --Roger Brinner