Re: Backend problem with large objects

What do we do with this.  Is it already done?  Looks quite old.


> Well, after a delay of a lot of months (sorry, huge personal crises!) I am
> happy to report that this works now, at least on a cursory test. I'll hit
> on it a bit harder soon and report back, but hopefully this patch'll be in
> time for 6.5? Certainly it works better now than before so maybe include
> the patch anyway, even if there isn't time to do better testing.
> 
> Cheers, and many many thanks Tatsuo.
> 
> Ian
> 
> ---------- Forwarded message ----------
> Date: Fri, 12 Feb 1999 23:12:07 +0900
> From: Tatsuo Ishii <t-ishii@sra.co.jp>
> To: t-ishii@sra.co.jp
> Cc: Ian Grant <I.A.N.Grant@damtp.cam.ac.uk>,
>     Bruce Momjian <maillist@candle.pha.pa.us>, pgsql-hackers@postgreSQL.org
> Subject: Re: [HACKERS] Backend problem with large objects 
> 
> > >Many thanks indeed for this. Unfortunately it doesn't completely work:  it
> > >fixes the problem as reported, but when, instead of writing five
> > >characters, one at a time, I write five at once, the backend dies in
> > >the same place it did before. Here's the C code slightly modified to
> > >reproduce the problem:
> > 
> > Give me some time. I'm not sure if I could solve new problem, though.
> > --
> > Tatsuo Ishii
> 
> I think I have fixed the problem you mentioned. Ian, could you apply
> included patches and test again? Note that those are for 6.4.2 and
> additions to the previous patches.
> 
> BTW, lobj strangely added a 0 filled disk block at the head of the
> heap. As a result, even 1-byte-user-data lobj consumes at least 16384
> bytes (2 disk blocks)! Included patches also fix this problem.
> 
> To Bruce:
> Thanks for taking care of my previous patches for current.  If
> included patch is ok, I will make one for current.
> 
> ---------------------------- 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    Fri Feb 12 20:21:05 1999
> ***************
> *** 624,648 ****
>           || obj_desc->offset < obj_desc->lowbyte
>           || !ItemPointerIsValid(&(obj_desc->htid)))
>       {
>   
>           /* initialize scan key if not done */
>           if (obj_desc->iscan == (IndexScanDesc) NULL)
>           {
> -             ScanKeyData skey;
> - 
>               /*
>                * As scan index may be prematurely closed (on commit), we
>                * must use object current offset (was 0) to reinitialize the
>                * entry [ PA ].
>                */
> -             ScanKeyEntryInitialize(&skey, 0x0, 1, F_INT4GE,
> -                                    Int32GetDatum(obj_desc->offset));
>               obj_desc->iscan =
>                   index_beginscan(obj_desc->index_r,
>                                   (bool) 0, (uint16) 1,
>                                   &skey);
>           }
> - 
>           do
>           {
>               res = index_getnext(obj_desc->iscan, ForwardScanDirection);
> --- 630,655 ----
>           || obj_desc->offset < obj_desc->lowbyte
>           || !ItemPointerIsValid(&(obj_desc->htid)))
>       {
> +         ScanKeyData skey;
> + 
> +         ScanKeyEntryInitialize(&skey, 0x0, 1, F_INT4GE,
> +                        Int32GetDatum(obj_desc->offset));
>   
>           /* initialize scan key if not done */
>           if (obj_desc->iscan == (IndexScanDesc) NULL)
>           {
>               /*
>                * As scan index may be prematurely closed (on commit), we
>                * must use object current offset (was 0) to reinitialize the
>                * entry [ PA ].
>                */
>               obj_desc->iscan =
>                   index_beginscan(obj_desc->index_r,
>                                   (bool) 0, (uint16) 1,
>                                   &skey);
> +         } else {
> +             index_rescan(obj_desc->iscan, false, &skey);
>           }
>           do
>           {
>               res = index_getnext(obj_desc->iscan, ForwardScanDirection);
> ***************
> *** 666,672 ****
>               tuple = heap_fetch(obj_desc->heap_r, SnapshotNow,
>                                  &res->heap_iptr, buffer);
>               pfree(res);
> !         } while (tuple == (HeapTuple) NULL);
>   
>           /* remember this tid -- we may need it for later reads/writes */
>            ItemPointerCopy(&tuple->t_ctid, &obj_desc->htid);
> --- 673,679 ----
>               tuple = heap_fetch(obj_desc->heap_r, SnapshotNow,
>                                  &res->heap_iptr, buffer);
>               pfree(res);
> !         } while (!HeapTupleIsValid(tuple));
>   
>           /* remember this tid -- we may need it for later reads/writes */
>            ItemPointerCopy(&tuple->t_ctid, &obj_desc->htid);
> ***************
> *** 675,680 ****
> --- 682,691 ----
>       {
>           tuple = heap_fetch(obj_desc->heap_r, SnapshotNow,
>                              &(obj_desc->htid), buffer);
> +         if (!HeapTupleIsValid(tuple)) {
> +           elog(ERROR,
> +                "inv_fetchtup: heap_fetch failed");
> +         }
>       }
>   
>       /*
> ***************
> *** 746,757 ****
>   
>       nblocks = RelationGetNumberOfBlocks(hr);
>   
> !     if (nblocks > 0)
>           buffer = ReadBuffer(hr, nblocks - 1);
> !     else
>           buffer = ReadBuffer(hr, P_NEW);
> ! 
> !     page = BufferGetPage(buffer);
>   
>       /*
>        * If the last page is too small to hold all the data, and it's too
> --- 757,771 ----
>   
>       nblocks = RelationGetNumberOfBlocks(hr);
>   
> !     if (nblocks > 0) {
>           buffer = ReadBuffer(hr, nblocks - 1);
> !         page = BufferGetPage(buffer);
> !     }
> !     else {
>           buffer = ReadBuffer(hr, P_NEW);
> !         page = BufferGetPage(buffer);
> !         PageInit(page, BufferGetPageSize(buffer), 0);
> !     }
>   
>       /*
>        * If the last page is too small to hold all the data, and it's too
> ***************
> *** 865,876 ****
>   
>           nblocks = RelationGetNumberOfBlocks(hr);
>   
> !         if (nblocks > 0)
>               newbuf = ReadBuffer(hr, nblocks - 1);
> !         else
>               newbuf = ReadBuffer(hr, P_NEW);
>   
> -         newpage = BufferGetPage(newbuf);
>           freespc = IFREESPC(newpage);
>   
>           /*
> --- 879,894 ----
>   
>           nblocks = RelationGetNumberOfBlocks(hr);
>   
> !         if (nblocks > 0) {
>               newbuf = ReadBuffer(hr, nblocks - 1);
> !             newpage = BufferGetPage(newbuf);
> !         }
> !         else {
>               newbuf = ReadBuffer(hr, P_NEW);
> +             newpage = BufferGetPage(newbuf);
> +             PageInit(newpage, BufferGetPageSize(newbuf), 0);
> +         }
>   
>           freespc = IFREESPC(newpage);
>   
>           /*
> ***************
> *** 973,978 ****
> --- 991,999 ----
>       WriteBuffer(buffer);
>       if (newbuf != buffer)
>           WriteBuffer(newbuf);
> + 
> +     /* Tuple id is no longer valid */
> +     ItemPointerSetInvalid(&(obj_desc->htid));
>   
>       /* done */
>       return nwritten;
> 
> 


--  Bruce Momjian                        |  http://www.op.net/~candle maillist@candle.pha.pa.us            |  (610)
853-3000+  If your life is a hard drive,     |  830 Blythe Avenue +  Christ can be your backup.        |  Drexel Hill,
Pennsylvania19026