MySQL Bugs: #24876: Access becomes very slow when using a full medium text field with MyODBC 5

Bug #24876	Access becomes very slow when using a full medium text field with MyODBC 5
Submitted:	7 Dec 2006 7:17	Modified:	10 Jul 2007 5:46
Reporter:	Erica Moss	Email Updates:
Status:	Closed	Impact on me:	None
Category:	Connector / ODBC	Severity:	S1 (Critical)
Version:	5.00.09	OS:	Windows (win XP sp 2/Access 2003)
Assigned to:	Jess Balint	CPU Architecture:	Any

Description:
The attached file is a mysqldump file of a small table like so:
Create Table: CREATE TABLE `testtable`
  `c1` int(11) NOT NULL auto_increment,
  `c2` mediumtext,
  PRIMARY KEY  (`c1`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.28 sec)

The table contains a single record with 16776960 bytes in the medium text field. Using the MyODBC 3.51 drivers it is possible to link to the table in Access, and create and open a form based on the table.  However if this is attempted using the 5.0 drivers Access will stop responding.  If much smaller data is used in this field then it works fine, but at some critical point memory starts leaking.

How to repeat:
1. Extrace the attached 7-zip file
2. Source the file into a mysql database
3. Link to the table (testtable) in Access
4. Create a form based on the linked table
5. Open the form

This same thing is happening with the larger text data types.  After further experimentation it appears that it's crashing because it's taking a long time to complete the query and I interrupted Access before it completed.  However this test is taking considerably longer to complete than it does under 3.51 where the table opens in about one second.

sql dump of test table

Attachment: testtable.7z (application/octet-stream, text), 15.14 KiB.

Committed in rev 712.

Access is not crashing, it's simply doing waaayyyy too much work. I've fixed the way partial-retrieval of strings is handled internally. It should complete in a "tolerable" amount of time now.

I've tested this patch and as Jess states, the behavior is certainly better than it was, in that the operation will complete and Access doesn't stop responding.  However a report which pointed to a medium/large text field that would open in roughly one second using the 3.51 driver is taking 15-20 seconds with 5.0 driver.

Fixed significantly, and pending release in 5.00.12.