I'd like to see comparisons on startup time between DBMS
based applications and Prevayler
based apps. Obviously, this isn't going to be your strong point, but it would help complete the picture, show how much you pay for the improvements mentioned above...
Sure. According to DouglasGiacomini, Prevayler
recovers 300.000 simple object creation commands in 50 seconds on his home PC (IDE hard-drive). I shall produce better benchmarks, though. If you have more results, please publish them here too. -- KlausWuestefeld
What about the impact of maintaining multiple indexes in a given entity? Obviously, for hierarchical storage and simple hash lookups, objects in memory are superior to databases. But when replacing a database, could you be losing some of the effeciencies of heavily optimized DB indexing techniques? In other words, if you use prevayler, do you have to become an indexing expert in order to balance memory usage for multiple indexes against performance considerations?
Hardly. Performance is a non-issue. In the WORST CASE
, indexing can be done exactly the same way your database does it @;) but without inter-process comunication and without object marshalling/unmarshalling. We are talking 3 to 4 orders of magnitude
The real issue is the complexity of your code. You can write indexing code yourself or you can use a library for that. See: HowDoIQueryMyObjects
? You are no longer restricted to indexing schemes that must work well with disk blocks, such as the database indexing schemes. --KlausWuestefeld
Can I suggest that without detailed configuration details of the box, these figures still don't mean that much to me. What's the memory size & speed? What sort of boxes are these running on? What's the IO subsystem like? It's all well & good to test these on my PC at home, but that hardly compares to the hardware I'd deploy to. That's where it really counts after all.
On every comparison, the same machine was used for Prevayler
and the database in question. Feel free, though, to run the tests on any hardware you want and publish your results here. --KlausWuestefeld
And what's that you say? In process operations are orders of magnitude faster than calling out to another system. WOW ;) You talk elsewhere about still being able to remote query using RMI, CORBA, JSP's perhaps... Can we see some performance comparisons based on these, where we're no longer talking about everything working in the same VM?
The client-to-appserver connection will be equally slow with Prevayler
or with a database. The appserver itself, though, is 3 to 4 orders of magnitude faster with Prevayler
because, as you well spotted, you can have a cohesive ObjectServer
in a single process. With the database/appserver architecture you cannot. That's precisely the point. --KlausWuestefeld
I need fault tolerance. Load balancing. Multiple VM's accessing the same data at once. How does it compare under these conditions?
Well, if you manage to put 9983 machines in an Oracle
cluster (with zero overhead, mind you), then you might get the same performance scalability as Prevayler
on a single machine. The best thing is we don't even have to discuss. Just run the tests. --KlausWuestefeld
What would be interesting is to test against an in-memory Java DB like McKoi ;-) --StephanSchmidt
Just do it. The test will run on anything that has a JDBC driver. --KlausWuestefeld
Yes, if I have some time left. But I guess we will change either way, because right now I think McKoi does heavy caching and SnipSnap
does heavy caching resulting in keeping the data twice in memory. --StephanSchmidt
"What are you waiting for? You're faster than this. Don't think you are, know you are..."
--Morpheus in The Matrix
Are you not comparing a Database that is using a remote protocol (JDBC in this case) to Prevayler
which is all in one VM?
Yes. This question was already asked and answered above. --KlausWuestefeld
Seems to me that to get an Apples/Apples comparison your benchmark should have a remote client (using RMI, or something like that).
No. Feel free to run your database in the same VM as the test. @;) --KlausWuestefeld
As a follow up to the above question - please don't dismiss the remote issue as "we dont need to do it that way". If this technology is going be accepted as a viable persistence mechanism, it is going to need to deal with multiple remote clients.
No. Persistence mechanisms do not have to "deal with" remote access. That would be coupling. They just have to "allow for" remote access. That is what "cohesion" means. --KlausWuestefeld
Security in particular is a concern. Having a remote protocol makes it much easier to control access to the data.
Doing access-control directly on data is brutally breaking encapsulation but, anyway, you are finally free to use whatever remote protocol you want. --KlausWuestefeld
Any non trivial application is going to have to use a remote protocol of some description. For example, if I am Bank - I am going to want some degree of isolation between my core transactional data and my application clients. RDBMS
provide some measure of isolation. Yes, I am free to use any remote protocol I want - but I have to use something - and your benchmark does not factor this in. Once again - I think your benchmark is not comparing apples to apples.
Don't get me wrong - I really like the idea of prevayler! Writing enterprise apps is very difficult - and a large part of that is dealing with impedance mismatch between the object and relational worlds. That being said, the issues of security, isolation, etc. are going to have to be dealt with if this technology is going to be usefull.
One approach might be to wrap Prevayler
in a distributed technology like Jini (using RIO, etc.). A persistent capable application could expose business methods (e.g. Account.updateBalance, etc.). You deploy a bundle of Biz Logic + Persistence to the persistence service. Remote clients can discover the service (via the lookup service) - and you get to leverage all the other Jini goodies (access control, robust service recovery, etc). Now that would be cool! I think there is a lot of potential synergy here. For example - your replication services could automagically discover each other. A deployed application could use the Quality of Service features of RIO to ask for the level of replication they desire.
-- Warren mailto:firstname.lastname@example.org
Simply: I AM
comparing apples to apples. You are wrong to state otherwise and that is not your point, anyway. Your point is: YOU ARE NOT INTERESTED
in apples. You are interested in REMOTE APPLES
. Regarding "remote apples" then, here we go again: The client-to-appserver connection will be equally slow with Prevayler or with a database. The appserver itself, though, is 3 to 4 orders of magnitude faster with Prevayler because, as you well spotted, you can have a cohesive Object Server in a single process. With the database/appserver architecture you cannot. That's precisely the point.
I like the Jini idea. --KlausWuestefeld
I think your claim of having an appserver that's 3 to 4 orders of magnitude faster with Prevayler
is valid for the case where a remote client (if it's an appserver, there are going to be remote clients) is making a single request that would result in a very complex query over several objects (thousands, it looks like). The performance of a Prevayler
-based appserver vs. a RDBMS
-based appserver would look different for the case of many remote remote clients resulting in a few queries each. I think Prevayler
would still be faster, but probably not 3 or 4 orders of magnitude faster. --Mark Kinzie
Data drilling and mining activities as well as huge batch processes, where no client interaction is involved, also benefit from the 3 to 4 orders of magnitude acceleration. But regarding small queries from remote clients you are certainly right. The server will still have to process network packets and format responses for the clients. Using Prevayler
, the time to execute the business query itself is negligible. Prevayler
actually raises the performance bar for all other components in your architecture. --KlausWuestefeld
I wonder if anyone would be prepared to generate some benchmarks for a Berkely DB based solution or similar. I would if I had the opportunity but I don't.