Ühel kenal päeval, P, 2006-12-03 kell 22:14, kirjutas Jim Nasby:
> On Nov 29, 2006, at 2:29 AM, Hannu Krosing wrote:
> > Ühel kenal päeval, K, 2006-11-29 kell 11:19, kirjutas Peter
> > Eisentraut:
> >> vacuumlazy.c contains a hint "Consider compacting this relation"
> >> but AFAICT,
> >> there is no indication anywhere how "compacting" is supposed to be
> >> achieved.
> >> I guess this means VACUUM FULL or CLUSTER, but I don't think the
> >> hint can be
> >> processed effectively by a user.
> >
> > I once had an online/concurrent/non-locking compacting script,
> > which did
> > for each const_pk_col_with_largest_ctid staring starting from end of
> > relation
> >
> > UPDATE rel
> > SET pk_col=pk_col
> > WHERE pk_col = const_pk_col_with_largest_ctid
> >
> > until the tuple moved to another page as determined by
> >
> > SELECT ctid FROM rel where pk_col=const_pk_col_with_largest_ctid
> >
> > if the tuple moved to a larger page number then it was time for
> > another
> > lazy vacuum.
>
> Larger or smaller?
Larger, smaller is the expected behaviour without vacuum.
> There's a TODO about allowing control over what pages in a relation
> you get back from FSM that would make this a lot easier. In the case
> of a bloated table, you'd want to have the FSM favor handing out
> pages at the beginning of the heap. If you combined that with a
> special mode where new tuples would not be created on any page in the
> last X percent of the heap, it would be trivial to clean up a bloated
> table. Theoretically, you might be able to apply the same kind of
> technique to cleaning up a bloated index.
>
> BTW, the other reason to allow selecting where the FSM hands out data
> is for keeping a table clustered.
FSM is consulted only in case the new tuple does not fit on the same
page as old. for clustering putposes, this should also be optional.
> You might also be able to keep
> indexes in a more optimal order on-disk (as I understand it, over
> time the physical order of an index can become very different from
> the index order).
> --
> Jim Nasby jim@nasby.net
> EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
>
>
--
----------------
Hannu Krosing
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