Stability and performance issue after 4.0 to 4.1 upgrade.

[Wolfgang Blauen]

I am having performance and stability problems with an existing application written in VB6 after an upgrade from 4.0.1 to 4.1.10.
The application uses the ODBC (3.51) connector to retrieve data from and update data in a MySQL database that was created in version 4.0.1.

Performance:
After an upgrade to Version 4.1.10 (and/or 4.1.0) the application has significant performance problems.
I have tested all hardware, OS (W2K) and network components and the server performs perfectly.
All tables are myISAM type with a mixture of fixed and dynamic row types.

Stability:
This is by far the more serious problem that showed up:

There seems to be some cross linking between records. i.e: "Select name, number from service where extrefno=436;" returns an empty record set while "Select name, number from service where extrefno>435 and extrefno<437;" returns the correct record (only ole exists in the table). An update query with the "... where extrefno=436 ... " clause resports 37 updated records (should be only 1 because “extrefno” is the primary key on the table). Similar things happen on deletes.
I’ve tried to dump the database and get an error number 23: “out of resources …” on several tables.
Dropping the tables resolves the issue but (naturally) I loose the data .
"Repair table ... extended" or "myisamcheck ..." do not find any problems and do not resolve the issue.

Any input is appreciated. Thanks in advance.