Re: [HACKERS] Backend problem with large objects

> 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 */