Problem/misunderstanding with ObjectCache, multiple databases and ObjectModification, 1.0.4

[Längerich, Bernd <B....@actosoft.de>]

Hi,

I have some problems understanding (and using) the concept of the cache when using multiple databases and determining the object modification level at the store method.

Assume we have two databases A and B with one being the default and one being the backup database. Both connections are configured using the cache:
       <object-cache class="org.apache.ojb.broker.cache.ObjectCacheDefaultImpl">
         <attribute attribute-name="timeout" attribute-value="-1"/>
       </object-cache>

Given the following code sequence with empty databases, I have some problems:

AnObject someObject = new AnObject();
[...]
PersistenceBroker defaultBroker = PersistenceBrokerFactory.defaultPersistenceBroker();
defaultbroker.store(someObject); // resulting in an INSERT to the default DB
[...]
defaultBroker.store(someObject); // resulting in an UPDATE to the default DB

PersistenceBroker backupBroker = PersistenceBrokerFactory.createPersistenceBroker(new PBKey("backup"));
backupBroker.store(someObject); // resulting in an UPDATE to the backup DB, which fails as there is no such row in the DB


As far as I understand the code from PersistanceBrokerImpl, it should query the cache and/or the DB:
        /*
        if PK values are set, lookup cache or db to see whether object
        needs insert or update
        */
        if (!insert)
        {
            insert = objectCache.lookup(oid) == null
                && !serviceBrokerHelper().doesExist(cld, oid, obj);
        }
        store(obj, oid, cld, insert);

The insert should be false, as the PK fields are not null, and the objectCache for the backupBroker should give null.
I traced with P6Spy, but I can't detect a SELECT to determine the existence of the row, so I assume the objectCache.lookup(oid) returns true.

Any hints?

Bernd

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Re: Problem/misunderstanding with ObjectCache, multiple databases and ObjectModification, 1.0.4

[Armin Waibel <ar...@apache.org>]

Hi Bernd,

Längerich wrote:
> Hi,
> 
> I have some problems understanding (and using) the concept of the cache when using multiple databases and determining the object modification level at the store method.
> 
> Assume we have two databases A and B with one being the default and one being the backup database. Both connections are configured using the cache:
>        <object-cache class="org.apache.ojb.broker.cache.ObjectCacheDefaultImpl">
>          <attribute attribute-name="timeout" attribute-value="-1"/>
>        </object-cache>
>
> Given the following code sequence with empty databases, I have some problems:
> 
> AnObject someObject = new AnObject();
> [...]
> PersistenceBroker defaultBroker = PersistenceBrokerFactory.defaultPersistenceBroker();
> defaultbroker.store(someObject); // resulting in an INSERT to the default DB
> [...]
> defaultBroker.store(someObject); // resulting in an UPDATE to the default DB
> 
> PersistenceBroker backupBroker = PersistenceBrokerFactory.createPersistenceBroker(new PBKey("backup"));
> backupBroker.store(someObject); // resulting in an UPDATE to the backup DB, which fails as there is no such row in the DB
>
> 
> As far as I understand the code from PersistanceBrokerImpl, it should query the cache and/or the DB:
>         /*
>         if PK values are set, lookup cache or db to see whether object
>         needs insert or update
>         */
>         if (!insert)
>         {
>             insert = objectCache.lookup(oid) == null
>                 && !serviceBrokerHelper().doesExist(cld, oid, obj);
>         }
>         store(obj, oid, cld, insert);
> 
> The insert should be false, as the PK fields are not null, and the objectCache for the backupBroker should give null.
> I traced with P6Spy, but I can't detect a SELECT to determine the existence of the row, so I assume the objectCache.lookup(oid) returns true.
> 
> Any hints?

You are right, OJB find the object in the cache (because you operate 
with the same objects on different DB's using a shared cache) and 
indicate to update the object instead of insert.

Do you really need a shared cache on your "backup" broker? I would 
recommend to use a "per broker cache" (for backup-broker)
http://db.apache.org/ojb/docu/guides/objectcache.html#ObjectCachePerBrokerImpl
Then OJB will not find the object in the cache of backup-broker and 
perform a DB select.

regards,
Armin

> 
> Bernd
> 
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> 

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