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 <[EMAIL PROTECTED]> 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 \
---------------------------(end of broadcast)---------------------------
TIP 4: Have you searched our list archives?
http://archives.postgresql.org
