Vacuum/mdtruncate() (was: RE: [HACKERS] Current TODO list)

On Mon, 24 May 1999, Hiroshi Inoue wrote:
> Backends would continue to access the file descritors already hold
> if vacuum does nothing about the invalidation of Relation Cache.

Yes, and I don't believe that is a problem. I may be wrong however...

First, please reverse my patch to mdtruncate() in md.c as soon as
possible. It does not work properly in some cases.

Second, I do have a better patch in the works. It is included below, but
DO NOT APPLY THIS!!! I would like someone to look it over quick. I have
checked the logic by hand for a few cases and done a bunch of tests. I
would like to test more first.

While doing a bunch of vacuums, I have seen some strange things(so my
patch probably isn't 100%).
I started with 58 segments, and did a bunch of delete/vacuums and got it
down to about 5-6. Then I got the error below while running a vacuum
analyze. This appeared after the index clean, but before any tuples were
moved.
ERROR: HEAP_MOVED_IN was not expected

Also, I was seeing some more errors about INDEX' TUPLES being higher than
HEAP TUPLES. Didn't this just get fixed, or did I break something with my
patch. I was seeing these after doing delete/vacuums with my patch.

Thanks,
Ole Gjerde

Index: src/backend/storage/smgr/md.c
===================================================================
RCS file: /usr/local/cvsroot/pgsql/src/backend/storage/smgr/md.c,v
retrieving revision 1.43
diff -u -r1.43 md.c
--- src/backend/storage/smgr/md.c 1999/05/17 06:38:41 1.43
+++ src/backend/storage/smgr/md.c 1999/05/24 06:30:25
@@ -712,32 +712,62 @@

#ifndef LET_OS_MANAGE_FILESIZE
int curnblk,
- i,
oldsegno,
- newsegno;
- char fname[NAMEDATALEN];
- char tname[NAMEDATALEN + 10];
+ newsegno,
+ lastsegblocks,
+ segcount = 0;
+ MdfdVec *ov,
+ *lastv;
+ MemoryContext oldcxt;

+ fd = RelationGetFile(reln);
curnblk = mdnblocks(reln);
- oldsegno = curnblk / RELSEG_SIZE;
- newsegno = nblocks / RELSEG_SIZE;

- StrNCpy(fname, RelationGetRelationName(reln)->data, NAMEDATALEN);
+ oldsegno = (curnblk / RELSEG_SIZE) + 1;
+ newsegno = (nblocks / RELSEG_SIZE) + 1;
+ oldcxt = MemoryContextSwitchTo(MdCxt);

- if (newsegno < oldsegno) {
- for (i = (newsegno + 1);; i++) {
- sprintf(tname, "%s.%d", fname, i);
- if (FileNameUnlink(tname) < 0)
- break;
+ if (newsegno < oldsegno && newsegno > 1)
+ {
+ lastv = v = &Md_fdvec[fd];
+ for (segcount = 1; v != (MdfdVec *) NULL;segcount++, v = v->mdfd_chain)
+ {
+ if(segcount == newsegno) /* Save pointer to last file
+ in the chain */
+ lastv = v;
+ if(segcount > newsegno)
+ {
+ FileUnlink(v->mdfd_vfd);
+ ov = v;
+ if (ov != &Md_fdvec[fd])
+ pfree(ov);
+ }
}
+ lastv->mdfd_chain = (MdfdVec *) NULL;
}
-#endif

+ /* Find the last file in the md chain */
+ for (v = &Md_fdvec[fd]; v->mdfd_chain != (MdfdVec *) NULL;)
+ v = v->mdfd_chain;
+
+ /* Calculate the # of blocks in the last segment */
+ lastsegblocks = nblocks - ((newsegno - 1) * RELSEG_SIZE);
+
+ MemoryContextSwitchTo(oldcxt);
+
+ if (FileTruncate(v->mdfd_vfd, lastsegblocks * BLCKSZ) < 0)
+ return -1;
+
+#else
+
fd = RelationGetFile(reln);
+
v = &Md_fdvec[fd];

if (FileTruncate(v->mdfd_vfd, nblocks * BLCKSZ) < 0)
return -1;
+
+#endif

return nblocks;