Design decision: where to put transaction?

Hello, Java expert and System Anlysis, Architect around the world, pls help me on this:
There are two type of EJB, namely Session EJB and Entity EJB. Both of them can be used to manipulate the data in database. So, for the transaction, such as withdraw money from a bank, Session EJB or Entity EJB is best used to implement that transaction?
Thanks.

Hello
It depends on where you want to control the work flow. If you are planning to use the session bean as a session facade, and process work flow by handling entity beans from with in its methods, you must handle transactions in the session beans.
So, you can call withDrawMoney(double amt) on the session bean from the client, the session bean will handle the transaction. You can even define the transaction demarcation at the method level.
As a rule, I would handle transaction in a session bean, if I am not handling business logic in the entity bean.
Hope this helps.
Shiva Kolli
Hello, Java expert and System Anlysis, Architect
around the world, pls help me on this:
There are two type of EJB, namely Session EJB and
Entity EJB. Both of them can be used to manipulate the
data in database. So, for the transaction, such as
withdraw money from a bank, Session EJB or Entity EJB
is best used to implement that transaction?
Thanks.

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Hi,
I'm building a 1 tier web shop, using mostly Ajax, Servlets and JPA and I need your advice on a design decision.
When a user demands to see the products belonging to a particular category of products, my DAO object returns to the servlet a java.util.List<Product>, where Product is a JPA entity. In the servlet class I "manually" create the Ajax XML response, the user gets to see the products, everything is nice and great.
I am not happy with the fact that the list of products remains detached in the servlet class, sort of say, and when another user demands to see the same products another list gets greated. These are objects that have method scope, but still they are on the stack, right? For 100 users who want to see 100 products each, the no. of objects created could cause the application to have a slower reponse time.
So my question is about the design of the application.
I obtain the list of products in the servlet class and construct the XML response. Right before sending the response, should I pass the list of products back to the DAO, and ask the EntityManager to merge the products? Will this reduce the no. of objects my application creates? Shouldn't I do this because I'm merging entities that have not been changed and the merge operation is time consuming?
Should I not pass back the products to the DAO and set each product in the list to reference null and call System.gc() ?
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first of all, a merge is only used to synchronize a changed entity that is not managed by an entity manager with the database. Why did you even come to the conclusion that you might need this?
No you don't nullify the entities in the list. You let the entire list go when you are done with it. Manually nullifying can hinder the garbage collector, just don't do it unless you have a very good reason for doing so.
Your main problem seems to be that you don't like the fact that you are fetching 100 objects for both users, putting duplicate objects in memory on the server. Are you sure this is a problem? You shouldn't be thinking about optimizations while you are still developing you know. I would wait until you are done, then profile the application to see where bottlenecks are; if fetching those 100 products turns out to take a lot of system resources, THEN optimize it.
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Where to put the commit in the FORALL BULK COLLECT LOOP

Hi,
Have the following LOOP code using FORALL and bulk collect, but didnt know where to put the
'commit' :
open f_viewed;
LOOP
fetch f_viewed bulk collect into f_viewed_rec LIMIT 2000;
forall i in 1..f_viewed_rec.count
insert into jwoodman.jw_job_history_112300
values f_viewed_rec(i);
--commit; [Can I put this 'commit' here? - Jenny]
EXIT when f_viewed%NOTFOUND;
END LOOP;
commit;
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mc**** wrote:
Bulk collect normally used with large data sets. If you have less dataset such as 1000-2000 records then you canot get such a performance improvent using bulk collect.(Please see oracle documents for this)
When you update records Oracle acquire exclusive lock for that. So if you use commit inside the loop then it will process number of records defined by limit parameter at ones and then commit those changes.
That will release all locks acquired by Oracle and also teh memory used to keep those uncommited transactions.
If you use commit outside the loop,
Just assume that you insert 100,000 records, all those records will store in oracle memory and it will affect all other users performance as well.
Further more if you update 100,000 records then it will hold exclusive lock for all 100,000 records addtion to the usage of the oracle memory.
I am using this for telco application which we process over 30 million complex records (one row has 234 columns).
When we work with large data sets we do not depends with the oracle basic rollback function. because when you keep records without commit itb uses oracle memory and badly slowdown all other processes.Hi mc****,
What a load of dangerous and inaccurate rubbish to be telling a new Oracle developer. Commit processing should be driven by the logical unit of a transaction. This should hold true whether that transaction involves a few rows or millions. If, and only if, the transaction is so large that it affects the size constraints of the database resources, in particular, rollback or redo space, then you can consider breaking that transaction up to smaller transactions.
Why is frequent committing undesirable I hear you ask?
First of all it is hugely wasteful of rollback or redo space. This is because while the database is capable of locking at a row level, redo is written at a block level, which means that if you update, delete or insert a million rows and commit after each individual statement, then that is a million blocks that need to go into redo. As many of these rows will be in the same block, if you instead do these as one transaction, then the same block in redo can be transacted upon, making the operation more efficient. True, locks will be held for longer, but if this is new data being done in batches then users will rarely be inconvenienced. If locking is a problem then I would suggest that you should be looking at how you are doing your processing.
Secondly, committing brings into play one of the major serialization points in the database, log sync. When a transaction is committed, the log buffer needs to be written to disc. This occurs serially for multiple commits. Each commit has to wait until the commit before has completed. This becomes even more of a bottleneck if you are using Data Guard in SYNC mode, as the commit cycle does not complete until the remote log is notified as written.
This then brings us two rules of thumb that will always lead a developer in the right direction.
1. Commit as infrequently as possible, usually at the logical unit of a transaction
2. When building transactions, first of all seek to do it using straight SQL (CTAS, insert select, update where etc). If this can't be easily achieved, then use PL/SQL bulk operations.
Regards
Andre

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Newbie here, so please be gentle and explicit (no detail is
too much to give or insulting to me).
I'm hoping one of you architecture/design gurus can help me
with this. I am trying to use good principals of design and not
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Again, the object that manages all that is instantiated on the main
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might have a button, on frame 2 and 3 nothing, on frame 4 maybe a
clip I allow the user to drag around etc. So I thought I would add
a layer to NavClip where I will have key frames and put the various
interactive assets on the appropriate key frames. So now I don't
know where to put the code that instantiates these objects (i.e.
the objects that know how to deal with the events and such for each
of these interactive assets). I tried putting the code on my main
timeline, but realized that I can't address the interactive assets
until the NavClip is on the frame that holds the particular asset.
I'm trying not to sprinkle code all over the place, so what do I
do? I thought I might be able to address the assets by just
providing a name for the asset and not a reference to the asset
itself, and then address the asset that way (i.e.
NavClip["interactive_mc"] instead of NavClip.interactive_mc), but
then I thought that's not good since I think there is no type
checking when you use the NavClip["interactive_mc"] form.
I hope I'm not being too dim a bulb on this and have missed
something really obvious. Thanks in advance to anyone who can help
me use a best practice.

1. First of all, the code should be:
var myDraggable:Draggable=new Draggable(myClip_mc);
myDraggable.initDrag();
Where initDrag() is defined in the Draggable class. When you
start coding functions on the timeline... that's asking for
problems.
>>Do I wind up with another object each time this
function is called
Well, no, but. That would totally depend on the code in the
(Draggable) class. Let's say you would have a private static var
counter (private static, so a class property instead of an instance
property) and you would increment that counter using a
setInterval(). The second time you enter the frame and create a new
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You shouldn't be using that, period. If you don't need the
asset anymore, delete it using the destroy() method. Again, if you
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define the Draggable class (class Draggable extends MovieClip) and
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library). In the Draggable class you can define a function unOnLoad
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don't need anymore to make sure we don't end up with all kinds of
stuff hanging around in the memory. When you extend the MovieClip
Class you can (additionally) use the onUnLoad event. And with the
code you posted, no it wouldn't delete the myClip_mc unless you
program it to do so.

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Hello,
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Design decision: where to put transaction?

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