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From:Joerg Bruehe Date:June 15 2005 10:56am
Subject:Re: InnnoDb - change innodb_buffer_pool_size ?
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Hello Michael!


Michael Gale wrote:
> Hello,
> 
>     I have finished reading something similer on the web, why is there a 
> 2GB limit ?

I assume you are using Linux on an x86 compatible machine (Pentium, 
Athlon, ...), so you have 32 bit addresses.
32 bit give you 4 G different values; as each address identifies a 
single byte, you can address 4 GB on the machine.

The Linux kernel differs between user and system addresses, this is 
essential to pass data around, for example in system calls.
Traditionally, this was done on the highest address bit (2 GB system 
address space, 2 GB user). With the growing size of applications, this 
has become configurable (with kernel generation) to a 1 / 3 ratio.

> 
> If I can compile the kernel to say eys there is 4GB of memory why can 
> mysql not use 3GB of it ?

But still these 3 GB (space of virtual addresses) must hold everything 
the application (in your case: MySQL) can address, so it contains code, 
stacks of all threads in the process, static data, all configurable 
buffers etc.

As a first step, you can use the "size" command on "mysqld" to get some 
of these values, then calculate the total thread stack space and add it.
Subtract that from your user address space size (2 or 3 GB), and 
distribute the result among all buffers, caches etc.

In any case, I see no way to use 3 GB just for the InnoDB buffer pool on 
a 32 bit system.


Joerg Bruehe

-- 
Joerg Bruehe, Senior Production Engineer
MySQL AB, www.mysql.com

Thread
InnnoDb - change innodb_buffer_pool_size ?Michael Gale15 Jun
  • RE: InnnoDb - change innodb_buffer_pool_size ?Partha Dutta15 Jun
    • Re: InnnoDb - change innodb_buffer_pool_size ?Michael Gale15 Jun
      • Re: InnnoDb - change innodb_buffer_pool_size ?Joerg Bruehe15 Jun
  • Re: InnnoDb - change innodb_buffer_pool_size ?Michael Gale15 Jun
    • Re: InnnoDb - change innodb_buffer_pool_size ?Jeff Smelser15 Jun