Re: Performance under contention

On 11/22/10 18:47, Kevin Grittner wrote:
> Ivan Voras<ivoras(at)freebsd(dot)org> wrote:
>
>> It looks like a hack
>
> Not to everyone. In the referenced section, Hellerstein,
> Stonebraker and Hamilton say:
>
> "any good multi-user system has an admission control policy"
>
> In the case of PostgreSQL I understand the counter-argument,
> although I'm inclined to think that it's prudent for a product to
> limit resource usage to a level at which it can still function well,
> even if there's an external solution which can also work, should
> people use it correctly. It seems likely that a mature admission
> control policy could do a better job of managing some resources than
> an external product could.

I didn't think it would be that useful but yesterday I did some
(unrelated) testing with MySQL and it looks like its configuration
parameter "thread_concurrency" does something to that effect.

Initially I thought it is equivalent to PostgreSQL's max_connections but
no, connections can grow (MySQL spawns a thread per connection by
default) but the actual concurrency is limited in some way by this
parameter.

The comment for the parameter says "# Try number of CPU's*2 for
thread_concurrency" but obviously it would depend a lot on the
real-world load.