Re: PostgreSQL

On Wed, Feb 01, 2006 at 06:58:04PM -0800, Alfred Perlstein wrote:
> 
> Also, thread to thread synchronization is somewhat faster than process
> to process synchronization.  Honestly, the default thread synchronization
> primitives typically blow the inter-process ones out of the water,
> although there are some OS's and libraries that provide relatively
> fast/cheap inter process syntonization.

It depends *very* strongly which mechanisms you use. If all you need and
want is a block mutex, you ultimately have to call the kernel for
synchronistation anyway -- both in forking and 1:1 threading.

Databases are different from many other applications in that they have a
wide range of possible lock points and it is not easy to even guess
where contention might be. For example, the discussed Postgres is pretty
reader lock free due to the Multi Version Commit system. MySQL is
different in that regard.

> Also, I'm pretty sure that synchronization between threads doesn't
> require locked bus cycles, only atomic ops, again another saving.

Ahem. How do you expect two threads on different CPUs to synchronise
correctly if no locked bus cycles are involved? It is important to
distinguish atomic operation and atomic bus locked operations after all
:-)

Joerg