On Thu, Mar 09, 2000 at 02:05:37AM +0100, Nicolas MONNET wrote:
> On Wed, 8 Mar 2000, Alan Cox wrote:
>
> |> If I remember properly, MySQL does not use mmaped files yet; if it would,
> |> would that make a difference? Currently it may just be busy copying
> |> buffers (I don't know how much of it is a userland issue vs. kernel
> |> space).
> |
> |When your I/O subsystem can do 100Mbytes/second sustained then maybe, but
> |with the PC of today - wildly improbable.
>
> I understand this; I mentioned earlier that in my case, MySQL isn't even
> swapping (300MB physical memory vs. 45MB db).
Its worth mentioning that MySQL uses a _really_ dumb locking strategy
which starves writers and causes db performance to suck really badly
when you have multiple concurrent readers and writers. We used to see
it here, and it brings the machine to its knees. To see if you're
hitting this, do "procinfo -d" and see if you're getting very large
numbers of context switches / sec.
If this is the case, its not a kernel issue, its a stupid app, and I
can give you a fairly crude workaround if you mail me in private.
Sean
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