Re: [DOCS] Autovacuum and XID wraparound

Alvaro Herrera wrote:
> However, given that Heikki just confirmed that CLUSTER does not freeze
> tuples, it's not really possible to do this, so I'll drop the CLUSTER
> patch for now.
>
> This means that people using CLUSTER to compact tables won't have the
> benefit of advancing relfrozenxid, so they will have to run VACUUM on
> those tables at some point anyway, even though there will be no dead
> tuples :-(

Now that I think this a bit more, I think CLUSTER should freeze the
tuples. I was worried about losing valuable debug information by doing
that, but thinking a bit more that's not a big concern: we wouldn't
freeze tuples newer than recent xmin. The update chain logic is the most
risky part of the code, and we wouldn't lose the xmin and xmax of tuples
that are part of update chains.

Patch attached. You'll need the changes to cluster.c to set the
relfrozenid as well.

--
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com
Index: src/backend/access/heap/rewriteheap.c
===================================================================
RCS file: /home/hlinnaka/pgcvsrepository/pgsql/src/backend/access/heap/rewriteheap.c,v
retrieving revision 1.3
diff -c -r1.3 rewriteheap.c
*** src/backend/access/heap/rewriteheap.c    17 Apr 2007 21:29:31 -0000    1.3
--- src/backend/access/heap/rewriteheap.c    16 May 2007 13:42:23 -0000
***************
*** 538,543 ****
--- 538,545 ----
      OffsetNumber    newoff;
      HeapTuple        heaptup;

+     heap_freeze_tuple(tup->t_data, state->rs_oldest_xmin, NULL);
+
      /*
       * If the new tuple is too big for storage or contains already toasted
       * out-of-line attributes from some other relation, invoke the toaster.