RE: [HACKERS] tables > 1 gig

> 
> > > Yes, I can see your point.  It would show them different views of the
> > > table.
> > >
> > > So, as you were saying, we have no way of invalidating file 
> descriptors
> > > of other backends for secondary segments.
> > 
> > > Why does truncating the file
> > > not work?  Any ideas?
> > >
> > 
> > I have gotten no bug reports for my trial implementation.
> > AFAIK,only Ole Gjerde has tested my patch.
> > Is it sufficient ?
> 
> Yes.  We need something, and maybe after we add it, people can do
> testing and find any problems.  It is better to apply it than to leave
> it as it currently exists, no?
>

OK,here is my patch for PostgreSQL6.5-release.

Regards.

Hiroshi Inoue
Inoue@tpf.co.jp

*** storage/smgr/md.c.orig    Fri Jun 11 12:20:06 1999
--- storage/smgr/md.c    Fri Jun 18 15:10:54 1999
***************
*** 674,684 ****     segno = 0;     for (;;)     {
!         if (v->mdfd_lstbcnt == RELSEG_SIZE
!             || (nblocks = _mdnblocks(v->mdfd_vfd, BLCKSZ)) == RELSEG_SIZE)         {
- 
-             v->mdfd_lstbcnt = RELSEG_SIZE;             segno++;              if (v->mdfd_chain == (MdfdVec *) NULL)
--- 674,685 ----     segno = 0;     for (;;)     {
!         nblocks = _mdnblocks(v->mdfd_vfd, BLCKSZ);
!         if (nblocks > RELSEG_SIZE)
!             elog(FATAL, "segment too big in mdnblocks!");
!         v->mdfd_lstbcnt = nblocks;
!         if (nblocks == RELSEG_SIZE)         {             segno++;              if (v->mdfd_chain == (MdfdVec *)
NULL)
***************
*** 711,732 ****     MdfdVec    *v;  #ifndef LET_OS_MANAGE_FILESIZE
!     int            curnblk;      curnblk = mdnblocks(reln);
!     if (curnblk / RELSEG_SIZE > 0)
!     {
!         elog(NOTICE, "Can't truncate multi-segments relation %s",
!             reln->rd_rel->relname.data);
!         return curnblk;
!     } #endif      fd = RelationGetFile(reln);     v = &Md_fdvec[fd];      if (FileTruncate(v->mdfd_vfd, nblocks *
BLCKSZ)< 0)         return -1;      return nblocks; 
 
--- 712,766 ----     MdfdVec    *v;  #ifndef LET_OS_MANAGE_FILESIZE
!     int            curnblk,
!                 i,
!                 oldsegno,
!                 newsegno,
!                 lastsegblocks;
!     MdfdVec            **varray;      curnblk = mdnblocks(reln);
!     if (nblocks > curnblk)
!         return -1;
!     oldsegno = curnblk / RELSEG_SIZE;
!     newsegno = nblocks / RELSEG_SIZE;
!  #endif      fd = RelationGetFile(reln);     v = &Md_fdvec[fd]; 
+ #ifndef LET_OS_MANAGE_FILESIZE
+     varray = (MdfdVec **)palloc((oldsegno + 1) * sizeof(MdfdVec *));
+     for (i = 0; i <= oldsegno; i++)
+     {
+         if (!v)
+             elog(ERROR,"segment isn't open in mdtruncate!");
+         varray[i] = v;
+         v = v->mdfd_chain;
+     }
+     for (i = oldsegno; i > newsegno; i--)
+     {
+         v = varray[i];
+         if (FileTruncate(v->mdfd_vfd, 0) < 0)
+         {
+             pfree(varray);
+             return -1;
+         }
+         v->mdfd_lstbcnt = 0;
+     }
+     /* Calculate the # of blocks in the last segment */
+     lastsegblocks = nblocks - (newsegno * RELSEG_SIZE);
+     v = varray[i];
+     pfree(varray);
+     if (FileTruncate(v->mdfd_vfd, lastsegblocks * BLCKSZ) < 0)
+         return -1;
+     v->mdfd_lstbcnt = lastsegblocks;
+ #else     if (FileTruncate(v->mdfd_vfd, nblocks * BLCKSZ) < 0)         return -1;
+     v->mdfd_lstbcnt = nblocks;
+ #endif      return nblocks;