key_buffer_size

[steve]

As anyone benchmarked if there is an advantage in setting
key_buffer_size in startup parameters. In a Linux environment, can
we not rely on Linux to cache the indecis?

I would prefer that, since then a large chunck of memory is not
dedicated to the keys, and mysql+Linux can dynamically decide how to
allocate memory.,

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[Missaka Wijekoon]

Re: key_buffer_size

That depends...

Yes Linux can cache portions the file system (your index) in memory,
however, MySQL will still have to make system calls to access those
indices. While the time to access a "cached" file is lower, you incur
the cost of system calls when the kernel has to mediate the reads on the
index files.

If MySQL has a larger key_buffer_size , then presumably it can access
that same data in userspace and be even faster.

As far as benchmarks are concerned, it really depends on the following
parameters (in no particular order):
1. How your data is indexed and queried.
2. The speed of your file system.
3. The layout of your file system - If the index and data files
are on different disks and/or controllers then it is even
better.
4. The amount of memory you have.
5. The speed and type of processor you have.

-Misk


steve wrote:[color=blue]
> As anyone benchmarked if there is an advantage in setting
> key_buffer_size in startup parameters. In a Linux environment, can
> we not rely on Linux to cache the indecis?
>
> I would prefer that, since then a large chunck of memory is not
> dedicated to the keys, and mysql+Linux can dynamically decide how to
> allocate memory.,
>[/color]