libpq questuion

Dmitry Samersoff wrote:

While update table whithin fetch forward loop
cause infinite fetching of updated touple?

(code fragment below cause infinite
displayng record with oid 20864)

----------------------------------------------------------------------------
PQexec(_conn, "BEGIN");
PQexec(_conn, "DECLARE curr1 CURSOR FOR select oid, name from domains;");

while(1)
{
_res = PQexec(_conn, "FETCH FORWARD 1 IN curr1");
if( PQresultStatus(_res) != PGRES_TUPLES_OK ) break;

PQexec(_conn, "update domains set type = 3 where oid = 20864" );
printf("oid: %s name: %s\n", PQgetvalue(_res,0,0),PQgetvalue(_res,0,1));
}
---------------------------------------------------------------------------

Which Postgres version?

I guess it is a side effect from the visibility of tuples
(records) in conjunction with portals (cursors).

The reason must be that the the UPDATE inside the loop add's
new tuples to the table at it's end. It also issues a
CommandCounterIncrement(), so the new tuples get visible to
the already running scan for the portal.

I planned to get my hands onto the visibility code in tqual.c
after v6.5 to prepare the system for deferred queries. I
have some things about it in mind, but must discuss the
details with Vadim before I start implementing it. They
interfere with MVCC.

Should I go for it before v6.5?

Jan

--

#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck@debis.com (Jan Wieck) #

Hello all,

-----Original Message-----
From: owner-pgsql-hackers@postgreSQL.org
[mailto:owner-pgsql-hackers@postgreSQL.org]On Behalf Of Jan Wieck
Sent: Monday, February 08, 1999 11:47 PM
To: dms@wplus.net
Cc: pgsql-hackers@hub.org
Subject: Re: [HACKERS] libpq questuion

Dmitry Samersoff wrote:

While update table whithin fetch forward loop
cause infinite fetching of updated touple?

(code fragment below cause infinite
displayng record with oid 20864)

------------------------------------------------------------------
----------

PQexec(_conn, "BEGIN");
PQexec(_conn, "DECLARE curr1 CURSOR FOR select oid, name from

domains;");

while(1)
{
_res = PQexec(_conn, "FETCH FORWARD 1 IN curr1");
if( PQresultStatus(_res) != PGRES_TUPLES_OK ) break;

PQexec(_conn, "update domains set type = 3 where oid = 20864" );
printf("oid: %s name: %s\n",

PQgetvalue(_res,0,0),PQgetvalue(_res,0,1));

}

------------------------------------------------------------------
---------

Which Postgres version?

I guess it is a side effect from the visibility of tuples
(records) in conjunction with portals (cursors).

The reason must be that the the UPDATE inside the loop add's
new tuples to the table at it's end. It also issues a
CommandCounterIncrement(), so the new tuples get visible to
the already running scan for the portal.

Current cursors are strangely sensitive in some cases.
So 4 months ago,I requested INSENSITIVE cursors..
I'm very happy if you will implement INSENSITIVE cursors.

And all cursors will be INSENSITIVE even if there are no
INSENSITIVE keywords ?

Thanks.

Hiroshi Inoue
Inoue@tpf.co.jp