Re: TOAST usage setting

Zeugswetter Andreas ADI SD wrote:
>
> > > The big question is do we want to drop the target tuple  size down
> to
> > > 512, and increase the chunk size to 8k for 8.3?  Dropping the tuple
> > > size down to 512 is going to give us some smaller TOAST values to
> fill
> > > in free space created by the 8k chuck size, assuming you have both
> > > types of values in the table.  Do we want to increase the access
> time
> > > of long TOAST by 6% if it means having more wasted space for lots of
>
> > > 4.1k values?
> >
> > If we do that people could see their disk space usage increase by up
> to
> > 16x: currently 513 bytes fits in heap and takes (roughly) 513
> > bytes;
>
> No, you misunderstood. Bruce was suggesting changing the target to 512.
> That means if a row is wider than ~2k, toaster will try to toast until
> the base row is
> ~512 bytes. I would not do that part for 8.3.

OK, what do you suggest for 8.3?  Attached are my suggestion to use 512
and a 4k chunk size, which I think means that 2.7k is the worst values
that has a loss of around 25%.

--
  Bruce Momjian  <bruce@momjian.us>          http://momjian.us
  EnterpriseDB                               http://www.enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +
Index: src/include/access/tuptoaster.h
===================================================================
RCS file: /cvsroot/pgsql/src/include/access/tuptoaster.h,v
retrieving revision 1.35
diff -c -c -r1.35 tuptoaster.h
*** src/include/access/tuptoaster.h    6 Apr 2007 04:21:43 -0000    1.35
--- src/include/access/tuptoaster.h    2 Jun 2007 02:52:22 -0000
***************
*** 42,48 ****
   * given to needs_toast_table() in toasting.c before unleashing random
   * changes.
   */
! #define TOAST_TUPLES_PER_PAGE    4

  /* Note: sizeof(PageHeaderData) includes the first ItemId on the page */
  #define TOAST_TUPLE_THRESHOLD    \
--- 42,48 ----
   * given to needs_toast_table() in toasting.c before unleashing random
   * changes.
   */
! #define TOAST_TUPLES_PER_PAGE    16

  /* Note: sizeof(PageHeaderData) includes the first ItemId on the page */
  #define TOAST_TUPLE_THRESHOLD    \
***************
*** 69,75 ****
   *
   * NB: Changing TOAST_MAX_CHUNK_SIZE requires an initdb.
   */
! #define EXTERN_TUPLES_PER_PAGE    4                /* tweak only this */

  /* Note: sizeof(PageHeaderData) includes the first ItemId on the page */
  #define EXTERN_TUPLE_MAX_SIZE    \
--- 69,75 ----
   *
   * NB: Changing TOAST_MAX_CHUNK_SIZE requires an initdb.
   */
! #define EXTERN_TUPLES_PER_PAGE    2                /* tweak only this */

  /* Note: sizeof(PageHeaderData) includes the first ItemId on the page */
  #define EXTERN_TUPLE_MAX_SIZE    \