[DB-SIG] mxODBC is truncating BLOBs when reading them

[Friedlander Paul]

Thanks for getting back to me.

First of all, here is the traceback:

>>> c.execute("SELECT raw_data FROM datasets LIMIT 1")
>>> a = c.fetchall()
Traceback (most recent call last):
  File "<interactive input>", line 1, in ?
Warning: ('01004', -2, 'Fetched item was truncated.', 3480)

As for the setup. I am using ActivePython V2.2 and the latest stable release
of mxODBC. Postgres is running
on a Linux box and I am running the client on Windows 2000. The ODBC driver
(running on windows) is from insight distribution systems (version
7.01.00.09, PSQLODBC.DLL, 11/27/01).

I was originally using the ODBC driver that comes with ActivePython. It
worked correctly (the data was returned correctly). However, reading BYTEA
columns seemed to make it unstable and crashed Python. All other operations
including writing BYTEA columns ran flawlessly. As a work around, I tried
mxODBC. I can query other types of fields but get the traceback above when I
try to query a BYTEA field. I haven't tried writing to a BYTEA field. 

The binary data is typically between 15k and 20k.

For the time being, I have ported the client application to linux using
psycopg but this isn't my prefered solution (it works fine in Linux).

Per the Postgres documentation, I am escaping "\", "'", and \x00. I think
that I have discovered that 0x0D characters are mysteriously disappearing
too and am looking into escaping them also.

I hope this gives you enough information to point me in a direction.

Thanks again.


-----Original Message-----
From: M.-A. Lemburg [mailto:mal@lemburg.com]
Sent: Tuesday, July 16, 2002 5:28 PM
To: Friedlander Paul
Cc: 'db-sig@python.org'
Subject: Re: [DB-SIG] mxODBC is truncating BLOBs when reading them


Friedlander Paul wrote:
> I am using mxODBC to retrieve data from a Postgres database. I am using
the
> latest ActivePython distribution.
> 
> When I read data from a column with BYTEA data I get a warning and am told
> that the data was truncated. I found a comment that this used to be a
> problem with MySQL databases but has been fixed.

Just guessing here since you don't provide enough information
(traceback, log file, versions, etc.): this could be related
to a network buffer problem or a problem with the ODBC driver
for Postgres. mxODBC doesn't truncate the data -- it's the
driver that's truncating it.

> I am using the Windows sub-object and am accessing the database through an
> ODBC converter provided by insight (running in the windows control panel).
> 
> Can anyone shed light on this?

Please post the traceback and give some hint about the size
of the data you are requesting.

Thanks,
-- 
Marc-Andre Lemburg
CEO eGenix.com Software GmbH
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