RE: New behavior cause data corruption in v11

[Joshua Fletcher]

Sounds right to me.  

-Josh

--
Josh Fletcher
4D Technical Services Team Member
http://www.4d.com

> -----Original Message-----
> From: David Dancy [mailto:david.dancy@...]
> Sent: Tuesday, November 10, 2009 6:02 PM
> To: 4D iNug Technical
> Subject: Re: New behavior cause data corruption in v11
>
> Alan,
>
> I think I've got this straight in my head. Let me see if I can get it
> out in words:
>
> At this point (AFAIK) triggers only run on one CPU/core on the server.
>
> The only change to the triggers mechanism in v11 from v2004 is that a
> trigger now no longer blocks access to the whole database. It only
> blocks access to the table it's running in, so you can have multiple
> triggers running at the same time, provided that they are for
> different tables.
>
> The triggers are all 4D language, which means that they execute in the
> cooperative thread maintained by the server on the client's behalf.
> Each client has a cooperative thread and a pre-emptive thread. The
> cooperative thread runs inside the 4D process, which means it's tied
> to one CPU/core. The OS may shift it to a different CPU/core, but the
> point is it's only running on one CPU/core at a time, and all the
> cooperative threads together run in the same CPU/core because they're
> all in the same process. The pre-emptive thread (I believe) can attach
> to any CPU/core. But since all triggers run in the cooperative thread
> for their client, although you may have multiple triggers going at
> once, they are all on the same CPU/core.
>
> If a trigger issues a query, that is handled by the server's DB
> engine, using as many threads as required. Since the DB engine threads
> are all pre-emptive, they can attach to any CPU/core as the OS sees
> fit. I think the trigger's cooperative thread will block until the
> results come back from the DB engine.
>
> Corrections/clarifications welcome.
>
> HTH
>
> David Dancy
> Sydney, Australia

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