Re: [HACKERS] Backend problem with large objects

Applied manually.  The patch did not apply cleanly, and needed a &tuple
in inv_wrold, not tuple.


> > On Tue, 2 Feb 1999, Tatsuo Ishii wrote:
> > 
> > > Reproduced here too. Seems very old and known problem of large object
> > > (writing into in the middle of a large object does not work).
> > 
> > Many thanks, does this mean it's not likely to be fixed? If so I'll take
> > this to the documentation list, if there is one. But first, can anyone
> > explain what *is* allowed in lo_write after lo_lseek? Is it OK to
> > overwrite a large object for example? 
> 
> Ok. I think I have found the source of the problem. Please apply
> included patches and try again.
> 
> > I also note that there is no way to truncate a large object without
> > reading the beginning bit and copying it out to another new large object,
> > which involves it going down the wire to the client and then back again. 
> > Are there any plans to implement lo_trunc or something? Perhaps this is
> > difficult for the same reason lo_write is difficult inside a large object.
> 
> Seems not too difficult, but I don't have time to do that.
> ---
> Tatsuo Ishii
> 
> ----------------------------- cut here ----------------------------------
> *** postgresql-6.4.2/src/backend/storage/large_object/inv_api.c.orig    Sun Dec 13 14:08:19 1998
> --- postgresql-6.4.2/src/backend/storage/large_object/inv_api.c    Thu Feb  4 22:02:43 1999
> ***************
> *** 545,555 ****
>               tuplen = inv_wrnew(obj_desc, buf, nbytes - nwritten);
>           else
>           {
> !             if (obj_desc->offset > obj_desc->highbyte)
>                   tuplen = inv_wrnew(obj_desc, buf, nbytes - nwritten);
>               else
>                   tuplen = inv_wrold(obj_desc, buf, nbytes - nwritten, tuple, buffer);
> !             ReleaseBuffer(buffer);
>           }
>   
>           /* move pointers past the amount we just wrote */
> --- 545,561 ----
>               tuplen = inv_wrnew(obj_desc, buf, nbytes - nwritten);
>           else
>           {
> !                   if (obj_desc->offset > obj_desc->highbyte) {
>                   tuplen = inv_wrnew(obj_desc, buf, nbytes - nwritten);
> +                 ReleaseBuffer(buffer);
> +             }
>               else
>                   tuplen = inv_wrold(obj_desc, buf, nbytes - nwritten, tuple, buffer);
> !             /* inv_wrold() has already issued WriteBuffer()
> !                which has decremented local reference counter
> !                (LocalRefCount). So we should not call
> !                ReleaseBuffer() here. -- Tatsuo 99/2/4
> !             ReleaseBuffer(buffer); */
>           }
>   
>           /* move pointers past the amount we just wrote */
> 
> 


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