Thread

Re: [QUESTIONS] Re: [HACKERS] text should be a blob field

Peter T Mount <psqlhack@maidast.demon.co.uk> — 1998-03-04T20:16:07Z

On Wed, 4 Mar 1998, Bruce Momjian wrote:

> > 1. Is there a call made by the backend to each datatype when a row is 
> >    deleted? I can't see one.
> 
> Well, you could have a RULE that deletes the large object at row
> deletion time.

As I haven't yet played with Rules & Triggers, and now we have 6.3 out of
the way, I'm going to start.

> However, if two rows point to the same large object, the first one
> deleting it would delete the large object for the other.  The only
> solution to this is to have a separate large object table, and use
> reference counts so only the last user of the object deletes it. 

Ah, in this case, there would be a single large object per column/row. If
the row is deleted, then so will the blob.

> > 2. When we update a row, we don't want the overhead of copying a very
> >    large blob when a row is first copied, then the original deleted, etc.
> 
> Again, a deletion-only rule, but if the update the row and change the
> large object, you would have to delete the old stuff.

That's true.

> Seems very messy to me.  Perhaps put all the large objects in a table,
> and have a process clean up all the unreferenced large objects.

I think that would be a last resort thing to use.

-- 
Peter T Mount  petermount@earthling.net or pmount@maidast.demon.co.uk
Main Homepage: http://www.demon.co.uk/finder
Work Homepage: http://www.maidstone.gov.uk Work EMail: peter@maidstone.gov.uk