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 */