Bug #5109 Crash with key_buffer_size>4GByte (64 Bit System)

Description:
If the key_buffer_size is increased beyond 4 GByte (either on startup, or while 
mysql is running with 'set global'), mysqld will run happily until it actually attempts to 
increase the key_buffer beyond 4 GByte. As soon as the key buffer exceeds 4 GByte, it 
crashes. 
 
If it is 'illegal' to use key buffers that large, I would expect an error message (or that it 
just ignores the larger setting). 
 
This is on a Suse 9.1 system for AMD64, using the x86_64 version of mysql 
(recompiled from src rpms) 
 
Overall, mysql happily uses more then 4 GBytes total. Just not for the key buffer. 

How to repeat:
1. start mysql 
2. set global key_buffer_size=5000000000 
3. issue queries until the key_buffer exceeds 4 GByte 

Suggested fix:
either ignore key_buffer_size settings that exceed 4 GByte, or move to a 64 bit 
implementation.

Can you provide us with an access to your machine.

If you could, we would like to have 6 GB or more available for testing. 

Is that possible.

If yes, send us your e-mail address, so that we can exchange keys privately.

no, we don't really need this, thank you very much.

We have an 8GB box in-house.

Hi,

Just to verify, what distribution are you using?  I see the version, but what did you download 
from the website (filename)?  I just want to make sure that you are using a 64 bit version of 
MySQL as well.

Best Regards

I am using the 64 bit version of mysql. I downloaded the src rpm from mysql.com 
(4.0.20-0) and rebuild it for the 'x86_64' target. At the time, the binary rpm would 
not run at all (separate bug which I think has been resolved by now)

Hi,

I was unable to repeat this crash 4.0.20 or 4.1.4, both compiled on an SGI Altix box with IA 64 
processors.  I set the key buffer to 6GB.

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1 to server version: 4.0.20

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql> show variables like "key_buffer_size";
+-----------------+------------+
| Variable_name   | Value      |
+-----------------+------------+
| key_buffer_size | 6442450944 |
+-----------------+------------+
1 row in set (0.00 sec)

Please let me know what binary installation you downloaded.

Best Regards

Hi,

I apologize, you had already mentioned the installation method you used.  I'm sorry you had to 
provide that again.

So you can set the key_buffer to 5GB but you can use more than 4GB?  This may be related to 
this bug:
http://bugs.mysql.com/bug.php?id=3827

When you see the limit reached, see what top reports as the total memory usage for mysqld?

Best Regards

reopened for more testing

Hi,

We're still looking into this.  We're trying to get an AMD64 machine set up with > 4GB of memory 
to see if it's glibc, something with the thread library or anything else.

We will update this bug ASAP.

Best Regards

The problem is that you should have been prevented from setting key_buffer_size larger than 4GB (bug 5731 relates to that), which is the maximum value supported currently.  This does result in a crash once actual key buffer usage exceeds the real amount of RAM allocated, however I am going to mark this as a duplicate of 5731, as a fix for that will prevent this crash.