Re: 9.3: load path to mitigate load penalty for checksums

On Tue, 2012-06-12 at 18:02 -0400, Tom Lane wrote:
> Or (d) it's not a problem, since the inserting XID is still busy
> according to the readers' snapshots.

How much of a savings did we get from PD_ALL_VISIBLE when it was added
into the page-at-a-time visibility check?

>From 608195a3a3656145a7eec7a47d903bc684011d73:

"In addition to the visibility map, there's a new PD_ALL_VISIBLE flag on
each heap page, also indicating that all tuples on the page are visible
to all transactions. It's important that this flag is kept up-to-date.
It is also used to skip visibility tests in sequential scans, which
gives a small performance gain on seqscans."

If "small" means that it's something we can give up, then focusing on
HEAP_XMIN_COMMITTED makes sense. But if we can't give it up, then we
need to take it into account in the proposal.

Regards,Jeff Davis