Re: MYSQL,Linux & large threads number

[Bill Davidsen]

On Fri, 15 Mar 2002, Peter Zaitsev wrote:

> Hello mysql,
> 
>   Some time ago I wrote about slow down of mysql with large number of
>   threads, which is quite common in Linux-Apache-Mysql-PHP enviroment.
> 
>   The test was simulating the worst case of concurrency - all the
>   threads are modified global variable in a loop 5000000 times in
>   total, using standard mutex for synchronization. The yeild is used
>   in a loop to force even more fair distribution of lock usage by
>   threads and increase context switches, therefore it did not change
>   much with large number of threads. I.e with 64 threads time without
>   yeild is 1:33.5

> For Next test I'll try to use Ingo's scheduler to see if it helps to
> solve the problem, also I'll try to test real mysql server to see
> which slowdown it will have.

I think it would be instructive to try using NGPT and either a patched
kernel or 2.4.19-pre3 which has the extra system calls included. I make no
predictions, but large improvements have been noted with a large number of
threads.

> 
> 
> 
> 
> CODE: (Dumb one just for test)
> 
>   
> #include <stdio.h>
> #include <pthread.h>
> #include <time.h>
> #define NUM_TH 1000

You might want to read this from the command line as an option and malloc
the vecors. Just a thought, I'm bad at guessing how lare a test I may want
to run.

-- 
bill davidsen <[e-mail]>
  CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.