Re: Threads

On Tue, 2003-01-07 at 12:21, Greg Stark wrote:
> Greg Copeland <greg(at)CopelandConsulting(dot)Net> writes:
>
> > That's the power of using the process model that is currently in use. Should
> > it do something naughty, we bitch and complain politely, throw our hands in
> > the air and exit. We no longer have to worry about the state and validity of
> > that backend.
>
> You missed the point of his post. If one process in your database does
> something nasty you damn well should worry about the state of and validity of
> the entire database, not just that one backend.
>

I can assure you I did not miss the point. No idea why you're
continuing to spell it out. In this case, it appears the quotation is
being taken out of context or it was originally stated in an improper
context.

> Are you really sure you caught the problem before it screwed up the data in
> shared memory? On disk?
>
>
> This whole topic is in need of some serious FUD-dispelling and careful
> analysis. Here's a more calm explanation of the situation on this particular
> point. Perhaps I'll follow up with something on IO concurrency later.
>

Hmmm. Not sure what needs to be dispelled since I've not seen any FUD.

> The point in consideration here is really memory isolation. Threads by default
> have zero isolation between threads. They can all access each other's memory
> even including their stack. Most of that memory is in fact only needed by a
> single thread.
>

Again, this has been covered already.

> Processes by default have complete memory isolation. However postgres actually
> weakens that by doing a lot of work in a shared memory pool. That memory gets
> exactly the same protection as it would get in a threaded model, which is to
> say none.
>

Again, this has all been covered, more or less. You're comments seem to
imply that you did not fully read what has been said on the topic thus
far or that you misunderstood something that was said. Of course, it's
also possible that I may of said something out of it's proper context
which may be confusing you.

I think it's safe to say I don't have any further comment unless
something new is being brought to the table. Should there be something
new to cover, I'm happy to talk about it. At this point, however, it
appears that it's been beat to death already.

--
Greg Copeland <greg(at)copelandconsulting(dot)net>
Copeland Computer Consulting