Re: HOT is applied

On 9/21/07, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>
>
> I'm also starting to come around to liking the page-header-xid field
> a bit more. I suggest that it could replace the "page is prunable"
> flag bit altogether --- to mark the page prunable, you must store
> some appropriate xid into the header field. This would avoid a useless
> prune attempt immediately after a page is marked prunable.
>
>
Agree. I was thinking of minimum of the following:

1 xmin of INSERT_IN_PROGRESS tuple
2 xmax of DELETE_IN_PROGRESS tuple
3 xmax of RECENTLY_DEAD_TUPLE

When we attempt a prune, we can set xid to the minimum of the above
three. If none of the above tuples exist in the page, xid can be set to
FrozenXid
A page need not be pruned if its xid is set to FrozenXid or is greater
than OldtestXmin.

In addition, I guess we can even set the xid also when we insert,
delete or update from the page unless its already set to a lower value.

Thanks,
Pavan

--
Pavan Deolasee
EnterpriseDB http://www.enterprisedb.com