Re[5]: [JBoss-user] Page by Page iteration

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Yes, but with commit option A data is still in the cache and no need
to go to the db.

alex

Tuesday, May 06, 2003, 3:56:56 PM, julien viet wrote:

jv> per spec, cmr collections are meant to be used in the transaction
jv> that created it and discarded after.

jv> julien

Dnc>> Julien,

Dnc>> The JBossCMP book seems to indicate that this is not the case w/ commit
Dnc>> option B:

Dnc>> "JBossCMP assumes that there is more than one user of the database but
Dnc>> keeps the
Dnc>> context information about entities between transactions. This context
Dnc>> information is used
Dnc>> for optimizing loading of the entity. [20]This is the default commit
Dnc>> option."

Dnc>> is that wrong, or am I just misunderstanding it? (I would have assumed that
Dnc>> the "context" info mentioned there was the list cache data).

Dnc>> If so, why would on_load be any better than on_find -- just because you may
Dnc>> load less data depending on when you stop iterating through the collection?

julien>>> you can associate a read-ahead on_load with the size of the
julien>>> limit parameter.

Dnc>> But then you need to find a way to ensure that the on_load page-size in the
Dnc>> deployment descriptor and the limit paramether your code passes in stay in
Dnc>> sync. Can LIMIT take a literal?

Dnc>> And wouldn't on_find work just as well in this case (since you're certain
Dnc>> you're going to read all the returned entries unless an exception occurs).

Dnc>> Dave

Dnc>>                       julien viet                                                                                                          
Dnc>>                       <ju...@jb...>                 To:       "Dav...@na..." <jbo...@li...>            
Dnc>>                       Sent by:                           cc:                                                                               
Dnc>>                       jbo...@li...ur        Subject:  Re[2]: [JBoss-user] Page by Page iteration                              
Dnc>>                       ceforge.net                                                                                                          

Dnc>>                       05/06/2003 07:41 AM                                                                                                  
Dnc>>                       Please respond to                                                                                                    
Dnc>>                       jboss-user                                                                                                           

Dnc>>> Can't you use read-ahead w/ on_load strategy? I.e., in
Dnc>> jbosscmp-jdbc.xml,
Dnc>>> have something like:
Dnc>> this will not work because you cannot cache a collection
Dnc>> between transactions.

Dnc>> what you should try is the use of JBossQL limit offset :
Dnc>> SELECT OBJECT(o) FROM object AS o ORDER BY o.id OFFSET ?1 LIMIT ?2

Dnc>> this will give you what you want. this will work efficiently
Dnc>> on relatively small size collection < 10000.

Dnc>> you can associate a read-ahead on_load with the size of the limit
Dnc>> parameter.

Dnc>> julien

Dnc>>> Can't you use read-ahead w/ on_load strategy? I.e., in
Dnc>> jbosscmp-jdbc.xml,
Dnc>>> have something like:

Dnc>>> <entity>
Dnc>>>       <ejb-name>MyEJB</ejb-name>
Dnc>>>       <query>
Dnc>>>             <query-method>
Dnc>>>                   <method-name>findAll_paged</method-name>
Dnc>>>                   <method-params/>
Dnc>>>             </query-method>
Dnc>>>             <jboss-ql><![CDATA[SELECT OBJECT(o) FROM my_table o ORDER
Dnc>> BY
o.somefield]]>>>></jboss-ql>
Dnc>>>             <read-ahead>
Dnc>>>                   <strategy>on_load</strategy>
Dnc>>>                   <page-size>20</page-size>
Dnc>>>             </read-ahead>
Dnc>>>       </query>
Dnc>>> </entity>

Dnc>>> Then your finder will pre-load the data for the first 20 rows into the
Dnc>>> pre-load cache, and I believe that when you iterate to #21 it'll grab
Dnc>> the
Dnc>>> data for the next 20.

Dnc>>> I'm not sure how this works when you throw CMR into the mix.

Dnc>>> And of course, it's not portable.

Dnc>>> Dave

Dnc>>>                       "Brian McSweeney"

Dnc>>>                       <bri...@au...        To:
Dnc>> <jbo...@li...>
Dnc>>>                       >                                  cc:

Dnc>>>                       Sent by:                           Subject:
Dnc>> [JBoss-user] Page by Page iteration
Dnc>>>                       jbo...@li...ur

Dnc>>>                       ceforge.net

Dnc>>>                       05/06/2003 05:51 AM

Dnc>>>                       Please respond to

Dnc>>>                       jboss-user

Dnc>>> Hi everyone,

Dnc>>> I'm looking for a little advice. I'm implementing a struts-jboss web
Dnc>> app
Dnc>>> which
Dnc>>> uses page-by-page data iteration. On the ejb side I'm using session
Dnc>> facades
Dnc>>> with cmp & cmr entity beans. However, in order to get the relevant
Dnc>> data
Dnc>>> back
Dnc>>> to iterate over, I currently have to utilise findAll, to retrieve a
Dnc>>> collection of
Dnc>>> entity beans.

Dnc>>> This is surely not good - as the data gets large, I'm getting back
Dnc>>> thousands
Dnc>>> of ejbs, just to display the first 20 or 30 on the first page. I
Dnc>> presume
Dnc>>> the
Dnc>>> correct way to do this with raw sql would be something like:

Dnc>>> 1) Get a count of all the relevant rows
Dnc>>> 2) Select the first 20
Dnc>>> 3) For each next page, select 20 offsetting at the relevant point.

Dnc>>> Am I correct in this being the proper approach?

Dnc>>> However, I haven't used raw sql with ejbs and I'm not sure how to.
Dnc>>> Advice here please.

Dnc>>> Finally, if I use raw sql, are stored procedures the correct way to
Dnc>> go.
Dnc>>> I've been told that they are considerably faster.
Dnc>>> thanks for all your help,
Dnc>>> Brian