Hi
The info about DLM is from some Compaq and Oracle
employees who I know from Digital days.
While it is not confidential information
(the DLM is not being marketed as such) the
SW engineers have lifed the code from VMS -->
CompaqTRU64 (was Digital Unix on Alpha) -->
RDB Port to DUNIX.
Subsequently Oracle needed the DLM to keep RDB going,
sudenly realised that the DLM could be *really* useful :-)
and sub-licensed the code from Compaq.
What both Compaq and Oracle are marketing is clustering
with near linear scalability.
NB: If you use Oracle 9i RAC on non Compaq environemnts
the Oracle data must be on RAW partitions to get proper
performance. If on Compaq you can use the normal (AFC) file
system.
Sun also have a DLM like clustering capability, but not
as mature.
The BAD news - DLM is closed/proprietory. It is not being
licensed as such. It is part of True64 and Oracle.
Compaq to donate the DLM to GNU/FSF?
- I'd like to see that ;-)
My guess is if the PosgreSQL project wanted to implement
parallel homogenous clustering the project would need to
have the following:
1. Design and implemnent an OpenDLM
(possibly as a new open source project)
My guess, assuming input from ex Digits, DECUS and other
VMS people, 10-20 man years over 12-18 months
2. Linux/FreeBSD incorporate OpenDLM into file system
3. PostgreSQL use OpenDLM to manage all DB locking
Well! There's a macro road map if I've ever seen one!
Regards, Kym Farnik (mailto:kym@recalldesign.com)
-- Recall Design http://www.recalldesign.com
53 Gilbert Street, Adelaide, South Australia 5000
Direct: (61-8) 8217 0556
Fax: (61-8) 8217 0555
Mobile: 0438 014 007
Keith wrote:
> I've waited, well, more than a decade for someone to really start using
> the DLM, or something like it, in a really useful way again. Oddly, at
> the time VAXclusters flourished, database vendors (except for DEC;
> remember RDB?) seemed to go around the DLM and roll their own locking.
>
> A standard like this could be really useful in open source databases.
>
> * Is there a link that talks about the DLM being used in the RACs?
> Oracle's documentation doesn't seem to mention the DLM.
>
> * Is there anything open about the DLM spec or code? I.e., could it
> actually be used in a project like PostgreSQL?
>
> * Is there any open source equivalent?
>
> * Have you looked at any PostgreSQL code and thought about how the DLM
> might be incorporated? (I'm not even really much of a C coder, but the
> idea is exciting to me).
>
> I suspect a lot of folks on the list have no idea how useful something
> like the DLM could be.
>