[elephant-devel] BDB vs postmodern

[Ian Eslick]

I doubt that Elephant on postmodern is going to be faster than using  
CL-SQL to do direct ORM against Postgresql.  Despite the great work  
that Henrik and others have done with Postmodern, there are too many  
layers of abstraction in the architecture to overcome.  The real point  
of using Elephant is ease of use, rapid prototyping and the  
programming API, not absolute performance.

I do suspect that raw performance (using BDB) may be comparable or  
better to any SQL/ORM solution for some simple access patterns, but  
for complex queries and joins SQL is probably the better way to go.   
We have already seen various comments on the list about common  
features of SQL databases that Elephant is missing (like getting a  
COUNT without generating all the objects).


As for using BDB to do replication and distributed transactions - it's  
possible but no one has tried it.  Elephant would need some serious  
modifications as the transaction protocol is different and I think  
that you'd have to build your own Global Transaction Manager either in  
Lisp or as an additional C daemon.

It's also possible that there are architectural or performance issues  
in using Postgresql across multiple machines of which I am unaware -  
hopefully one of the PG experts will comment.

Ian

On Feb 20, 2008, at 9:47 PM, lists at infoway.net wrote:

> Well, this is certainly interesting, since this would allow me to  
> decouple the storage system from the lisp environment allowing the  
> possibility of setting up a cluster of lisp machines to handle  
> application logic. Isn't there a way to achieve this on BDB?
>
> We prefer to deploy our systems on clusters of "inexpensive"  
> machines in order to leverage hardware failures and it seems that  
> scalability of BDB/Lisp applications is achieved by scaling a single  
> machine.
>
> Now, postmodern being 4x slower could be an issue. However, how does  
> that compare to a regular CL-SQL and relational queries is a  
> different story. If postmodern is about the same speed as hitting  
> Postgres with CL-SQL and just using plain SQL instead of elephant,  
> at the end of the day, that's the performance our users are getting  
> anyway :)
>
> Thanks,
> Waldo
>
>>>
>>> Since Postgres does allow for features such as replication,  
>>> clustering, and fail-over with multiple active simultaneous client  
>>> connections, does this mean that I could have multiple (separate)  
>>> lisp clients using elephant connecting to a separate Postgres  
>>> cluster with no concurrency issues?
>>
>> Yes.
>>
>> You can do this on BDB, but only on the same system as it relies on  
>> shared memory locks between processes.  This helps for multi-CPU  
>> systems (one lisp process per CPU) but not for distributing  
>> Elephant across
>>
>>> Thanks,
>>> Waldo
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