RE: prefetch and autoRetreive

[John <wu...@mailandnews.com>]

I figured that would fix it, but I also figured that was in there for a reason 
and I didn't want to change something I didn't completely understand.  That's 
mainly why I asked why it had to be that way.

I'm the one that has the patch for deep-prefetching via joins, so I don't 
really care, because that usually works better for me.  I just wanted to bring 
the issue up in case anyone else had the same problem.  Thanks for the 
comments.

John

>===== Original Message From Jakob Braeuchi <jb...@gmx.ch> =====
>hi john,
>
>have you tried disabling the collection-desriptor tweaking in
>RelationshipPrefetcherImpl#prepareRelationshipSettings() ?
>
>public void prepareRelationshipSettings()
>{
>setCascadeRetrieve(getObjectReferenceDescriptor().getCascadeRetrieve());
>getObjectReferenceDescriptor().setCascadeRetrieve(false);  // comment it
>}
>
>
>jakob
>
>John wrote:
>> I sensed that, but I'm not sure the penalty for loading an object twice is 
is
>> bad as the penalty I was getting.  A lot of places in our code assume the
>> object reference is loaded on a required relationship.  One thread was
>> prefetching and turned off auto-retrieve, then another came in and thought
>> that was the right value and set it back to that.  So from then on none of 
the
>> objects had the relationship loaded and I got NullPointerException 
everywhere.
>>  I suppose that multiple loads could be more of an issue with the global
>> cache, but with cache-per-broker I'm not sure if that's an issue.  At least 
to
>> me double-load isn't as big a deal as the NPE's.  I had to discontinue 
using
>> prefetch in the couple of places I was using it.  (Not sure that's the 
worst
>> thing anyway, since I don't know that it helped a whole lot.)
>>
>> John
>>
>>
>>>===== Original Message From Jakob Braeuchi <jb...@gmx.ch> =====
>>>hi john,
>>>
>>>
>>>John wrote:
>>>
>>>
>>>Has there been any solution to this issue (OJB188)?  This bit me in the
>>
>> butt,
>>
>>>but of course it took quite a bit of digging and debugging to realize this
>>
>> is
>>
>>>what was happening.  Why exactly is the value changed while prefetching?
>>>
>>>
>>>auto-retrieve is disabled during prefetching of a relationship to avoid
>>>loading the same obj multiple times.
>>>
>>>jakob
>>>
>>>
>>>I have a patched version of OJB that was based on HEAD from the middle of
>>>August, so I haven't been able to update for a while (don't want to
>>
>> repatch).
>>
>>>It seems that there have been some changes to OJB since then with regards
>>
>> to
>>
>>>(proxy) prefetching, autoretrieve, etc, especially in how those are
>>
>> configured
>>
>>>in the repository.  Are these summarized anywhere?
>>>
>>>John Marshall
>>>Connectria
>>>
>>>
>>>=============================================
>>>Date: Fri, 11 Jul 2003 18:19:33 +0200
>>>From: Jakob Braeuchi <jb...@gmx.ch>
>>>Subject: Potential problem with prefetch-relationships ?
>>>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>>
>>>
>>>hi theo,
>>>
>>>during prefetch auto-retrieve is disabled. when an other thread uses the
>>>relationship-desriptor it will find auto-retrive off.
>>>this is a known problem but i do not have a solution for it :(
>>>
>>>
>>>jakob
>>>
>>>Theo Niemeijer wrote:
>>>
>>>
>>>
>>>>Hi all,
>>>>I seemed to have stumbled on a potential problem with
>>>>the "prefetch relationship" option in PB query.
>>>>
>>>>After using prefetchRelationship for retrieval of big list of results,
>>>>and at the same time performing other queries,
>>>>I seemed to have lost the "auto-retrieve" attribute on
>>>>the collection descriptor.
>>>>
>>>>The result was that subsequent queries did not
>>>>retrieve that collection anymore, probably because the
>>>>"auto-retrieve" was disabled.
>>>>
>>>>The problem is quite hard to reproduce, but my guess is
>>>>that different threads modified the repository descriptor
>>>>in the wrong sequence, by means of the setCascadeRetrieve
>>>>method used in prepareRelationshipSettings.
>>>>
>>>>I might be wrong, because I simply do not oversee all aspects
>>>>of OJB. But am I right to view this as a potential problem
>>>>in "concurrency situations" like websites ?
>>>>I do not feel too comfortable that OJB makes these "temporary"
>>>>changes to the repository model.
>>>>
>>>>Cheers,
>>>>	Theo Niemeijer
>>>
>>>
>>>
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>>>
>>>
>>>
>>>
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>>
>>
>>
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>>
>>
>
>
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Re: prefetch and autoRetreive

[Jakob Braeuchi <jb...@gmx.ch>]

hi john,

do you have an up-to-date version of this patch you could post on the list ?

jakob

John wrote:
> I figured that would fix it, but I also figured that was in there for a reason 
> and I didn't want to change something I didn't completely understand.  That's 
> mainly why I asked why it had to be that way.
> 
> I'm the one that has the patch for deep-prefetching via joins, so I don't 
> really care, because that usually works better for me.  I just wanted to bring 
> the issue up in case anyone else had the same problem.  Thanks for the 
> comments.
> 
> John
> 
> 
>>===== Original Message From Jakob Braeuchi <jb...@gmx.ch> =====
>>hi john,
>>
>>have you tried disabling the collection-desriptor tweaking in
>>RelationshipPrefetcherImpl#prepareRelationshipSettings() ?
>>
>>public void prepareRelationshipSettings()
>>{
>>setCascadeRetrieve(getObjectReferenceDescriptor().getCascadeRetrieve());
>>getObjectReferenceDescriptor().setCascadeRetrieve(false);  // comment it
>>}
>>
>>
>>jakob
>>
>>John wrote:
>>
>>>I sensed that, but I'm not sure the penalty for loading an object twice is 
> 
> is
> 
>>>bad as the penalty I was getting.  A lot of places in our code assume the
>>>object reference is loaded on a required relationship.  One thread was
>>>prefetching and turned off auto-retrieve, then another came in and thought
>>>that was the right value and set it back to that.  So from then on none of 
> 
> the
> 
>>>objects had the relationship loaded and I got NullPointerException 
> 
> everywhere.
> 
>>> I suppose that multiple loads could be more of an issue with the global
>>>cache, but with cache-per-broker I'm not sure if that's an issue.  At least 
> 
> to
> 
>>>me double-load isn't as big a deal as the NPE's.  I had to discontinue 
> 
> using
> 
>>>prefetch in the couple of places I was using it.  (Not sure that's the 
> 
> worst
> 
>>>thing anyway, since I don't know that it helped a whole lot.)
>>>
>>>John
>>>
>>>
>>>
>>>>===== Original Message From Jakob Braeuchi <jb...@gmx.ch> =====
>>>>hi john,
>>>>
>>>>
>>>>John wrote:
>>>>
>>>>
>>>>Has there been any solution to this issue (OJB188)?  This bit me in the
>>>
>>>butt,
>>>
>>>
>>>>but of course it took quite a bit of digging and debugging to realize this
>>>
>>>is
>>>
>>>
>>>>what was happening.  Why exactly is the value changed while prefetching?
>>>>
>>>>
>>>>auto-retrieve is disabled during prefetching of a relationship to avoid
>>>>loading the same obj multiple times.
>>>>
>>>>jakob
>>>>
>>>>
>>>>I have a patched version of OJB that was based on HEAD from the middle of
>>>>August, so I haven't been able to update for a while (don't want to
>>>
>>>repatch).
>>>
>>>
>>>>It seems that there have been some changes to OJB since then with regards
>>>
>>>to
>>>
>>>
>>>>(proxy) prefetching, autoretrieve, etc, especially in how those are
>>>
>>>configured
>>>
>>>
>>>>in the repository.  Are these summarized anywhere?
>>>>
>>>>John Marshall
>>>>Connectria
>>>>
>>>>
>>>>=============================================
>>>>Date: Fri, 11 Jul 2003 18:19:33 +0200
>>>>From: Jakob Braeuchi <jb...@gmx.ch>
>>>>Subject: Potential problem with prefetch-relationships ?
>>>>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>>>
>>>>
>>>>hi theo,
>>>>
>>>>during prefetch auto-retrieve is disabled. when an other thread uses the
>>>>relationship-desriptor it will find auto-retrive off.
>>>>this is a known problem but i do not have a solution for it :(
>>>>
>>>>
>>>>jakob
>>>>
>>>>Theo Niemeijer wrote:
>>>>
>>>>
>>>>
>>>>
>>>>>Hi all,
>>>>>I seemed to have stumbled on a potential problem with
>>>>>the "prefetch relationship" option in PB query.
>>>>>
>>>>>After using prefetchRelationship for retrieval of big list of results,
>>>>>and at the same time performing other queries,
>>>>>I seemed to have lost the "auto-retrieve" attribute on
>>>>>the collection descriptor.
>>>>>
>>>>>The result was that subsequent queries did not
>>>>>retrieve that collection anymore, probably because the
>>>>>"auto-retrieve" was disabled.
>>>>>
>>>>>The problem is quite hard to reproduce, but my guess is
>>>>>that different threads modified the repository descriptor
>>>>>in the wrong sequence, by means of the setCascadeRetrieve
>>>>>method used in prepareRelationshipSettings.
>>>>>
>>>>>I might be wrong, because I simply do not oversee all aspects
>>>>>of OJB. But am I right to view this as a potential problem
>>>>>in "concurrency situations" like websites ?
>>>>>I do not feel too comfortable that OJB makes these "temporary"
>>>>>changes to the repository model.
>>>>>
>>>>>Cheers,
>>>>>	Theo Niemeijer
>>>>
>>>>
>>>>
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>>>>For additional commands, e-mail: ojb-user-help@db.apache.org
>>>>
>>>>
>>>>
>>>>
>>>>---------------------------------------------------------------------
>>>>To unsubscribe, e-mail: ojb-user-unsubscribe@db.apache.org
>>>>For additional commands, e-mail: ojb-user-help@db.apache.org
>>>
>>>
>>>
>>>---------------------------------------------------------------------
>>>To unsubscribe, e-mail: ojb-user-unsubscribe@db.apache.org
>>>For additional commands, e-mail: ojb-user-help@db.apache.org
>>>
>>>
>>
>>
>>---------------------------------------------------------------------
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> 
> 
> 
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> 


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