Re: Binary Large Objects (LOB/BLOB) in Hibernate and JDBC: Unresolved issues

2012/1/9 Oliver Jowett <oliver(at)opencloud(dot)com>:
> Otherwise, what should JDBC do differently here? Be specific. It would

First, I pretty sure that Hibernate nor the Tomcat/Java GC are
misconfigured - since it works now after having installed the trigger
by hand.

To become more specific read the first two sections as a first hint
here in this official doc:
http://www.postgresql.org/docs/current/interactive/lo.html

I try to trace the JDBC calls coming from Hibernate (although the
problem seems to me pretty clearly located).
That investigation will take some time.

Yours, Stefan

2012/1/9 Oliver Jowett <oliver(at)opencloud(dot)com>:
> On 9 January 2012 14:29, Stefan Keller <sfkeller(at)gmail(dot)com> wrote:
>> 2012/1/9 Oliver Jowett <oliver(at)opencloud(dot)com>:
>>> As a LO is independent storage that might have multiple references to> it (the OID might be stored in many places), without explicit deletion> you need a GC mechanism to collect unreferenced LOs eventually -> that's what vacuumlo etc are doing.
>> I can follow that. But that's not what the JDBC user expects nor is it
>> explained (nor mentioned) in the JDBC docs.
>>
>> From a conceptual view I have just an entity MyWebcam with an
>> attribute called image. Attribute image is of attribute cardinality
>> 1:1 (and private):
>>
>> // Java using Hibernate/JPA:
>>  @Entity
>>  @Lob
>>  @Basic(fetch=FetchType.LAZY)
>>  public class MyWebcam {
>>    private byte[] image;
>>    private String name;
>>    public byte[] getImage() { return image; }
>>    public void setImage(byte[] _image) { image=_image; }
>>    // ... other stuff
>>  }
>>
>> That's the classic use case.
>> Isn't it obvious that if setImage() sets another byte[] that the image
>> space get's cleared by the layers below?
>> And since Hibernate chose to use one variant of JDBC, it's also JDBC
>> which has to take care about orphans.
>
> Well, either the Hibernate mapping is misconfigured, or your database
> is misconfigured i.e. you are not collecting garbage LOs. If you have
> a suitable GC mechanism configured, then what happens?
>
> Otherwise, what should JDBC do differently here? Be specific. It would
> be helpful if you could provide a native JDBC example, rather than a
> Hibernate example, since it's not clear what JDBC calls are being made
> by Hibernate.
>
> Oliver