I don't like any of the options...
(1) transaction timeout - bad performance; may force client to retry,
etc.
(2) reorganize logic to guarantee sequence -- not really feasible with
sophisticated recursive search algorithm.
(3) make entities re-entrant -- that's suitable for some methods but not
others on my entity.
(4) in "search" session bean, synchronize on a static mutex object to
serialize access to search bean -- easy fix, but not very scalable and
not sanctioned by EJB.
But I understand and I'll pick the least-terrible method.
Will the optimistic cache be the default in the future?
- Keith
-----Original Message-----
From: Nortje, Andrew <[EMAIL PROTECTED]>
To: 'jBoss' <[EMAIL PROTECTED]>
Date: Thursday, November 30, 2000 12:43 PM
Subject: RE: [jBoss-User] deadlock accessing EntityBeans
>Keith
>
>You can define your entity beans to be reentrant in ejb-jar.xml like
this.
>This might fix your problem. The J2EE spec discourages this, can't
remember
>the exact reasons right now...
>
> <entity>
> <description>Member Bean</description>
> <display-name>Member Bean</display-name>
> <ejb-name>Member</ejb-name>
> <home>com.uni.entity.myaccount.MemberHome</home>
> <remote>com.uni.entity.myaccount.Member</remote>
> <ejb-class>com.uni.entity.myaccount.MemberBean</ejb-class>
> <persistence-type>Bean</persistence-type>
> <prim-key-class>com.uni.entity.myaccount.MemberPK</prim-key-class>
> <reentrant>True</reentrant>
> <resource-ref>
> <res-ref-name>jdbc/UniteItDB</res-ref-name>
> <res-type>javax.sql.DataSource</res-type>
> <res-auth>Container</res-auth>
> </resource-ref>
> </entity>
>
>
>
>> -----Original Message-----
>> From: Rickard Oberg [mailto:[EMAIL PROTECTED]]
>> Sent: Thursday, November 30, 2000 12:24 PM
>> To: jBoss
>> Subject: Re: [jBoss-User] deadlock accessing EntityBeans
>>
>>
>> Hi!
>>
>> "Keith L. Musser" wrote:
>> > I have a SessionBean which performs a search on Entity Beans. The
>> > sequence in which the search accesses the Entity Beans
>> depends on call
>> > arguments to the session bean.
>> >
>> > When I invoke the session bean from multiple clients, I get
>> deadlock.
>> >
>> > This appears to be because search 1 assesses entity A
>> first, then entity
>> > B. Search 2, however, acesses entity B first, then entity A.
>> >
>> > So if the timing is just wrong, both searches get the first
>> entity, but
>> > cannot get the second, since it's locked by the other search.
>> >
>> > Is there a way to set up jboss.xml to prevent this from happening?
>>
>> This is a known issue with concurrent systems and pessimistic
>> concurrency schemes (which is what our cache uses). You should either
>> wait for transaction timeout and retry, or make sure that they are
>> always used in the same order.
>>
>> There are plans to make an optimistic concurrency cache which
>> would fix
>> this, but this will not be done for awhile.
>>
>> regards,
>> Rickar
>>
>> --
>> Rickard Oberg
>>
>> Email: [EMAIL PROTECTED]
>>
>>
>> --
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>
>
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