Too many mysqld instances

Hi.

We need to run mysql on a server with minimum memory usage. Currently,
there are running 3 mysqld instances and 1 mysqld_safe instances on the
linux box. How do I reduce the number of instances, I did not find a
corresponding setting in the config file.

Regards, Jan

Gordon Burditt schrieb:
> I believe Linux shows you threads with 'ps', so you've probably
> got 1 process, 3 threads for mysqld.
>
> I believe the mysqld variable 'max_connections' will control this,
> but you really don't want to set it below 3.

I think 'ps' shows all processes not threads. Both 'ps' and 'top' show
my two mysqld instances.

Regards, Jan

gordonb.wng7k@burditt.org (Gordon Burditt) wrote:
>>We need to run mysql on a server with minimum memory usage. Currently,
>>there are running 3 mysqld instances and 1 mysqld_safe instances on the
>>linux box. How do I reduce the number of instances, I did not find a
>>corresponding setting in the config file.
>
> I believe Linux shows you threads with 'ps', so you've probably
> got 1 process, 3 threads for mysqld.

It's threads definitely. Linux kernels below 2.6 don't show the
difference between threads and processes from user space.

> I believe the mysqld variable 'max_connections' will control this,
> but you really don't want to set it below 3.

Mysqld runs in multiple threads. There is one master thread, a variable
number of helper threads (log writer, replication, I/O) plus one thread
per client connection (worker threads). There is also a thread cache
for workers; it's size is conrolled by the thread_cache variable. Some
nonstandard features (i.e. replication) and storage engines (innodb)
start additional threads. AFAIK 3 threads is minimum.

As for memory consumption: mysqld threads are pretty lightweight. Most
buffers are shared. Each thread consumes it's own stack (192KB) sort
buffer, read buffer (default: 8M each) and local variables. Beside the
buffers thats approximately 300KB memory footprint per extra thread.


XL