Re: HOT latest patch - version 8

Heikki Linnakangas wrote:
> I have some suggestions which I'll post separately,

A significant chunk of the complexity and new code in the patch comes
from pruning hot chains and reusing the space for new updates. Because
we can't reclaim dead space in the page like a VACUUM does, without
holding the vacuum lock, we have to deal with pages that contain deleted
tuples, and be able to reuse them, and keep track of the changes in
tuple length etc.

A much simpler approach would be to try to acquire the vacuum lock, and
compact the page the usual way, and fall back to a cold update if we
can't get the lock immediately.

The obvious downside of that is that if a page is continuously pinned,
we can't HOT update tuples on it. Keeping in mind that the primary use
case for HOT is largeish tables, small tables are handled pretty well by
autovacuum, chances are pretty good that you can get a vacuum lock when
you need it.

Thoughts?

I'm looking for ways to make the patch simpler and less invasive. We may
want to put back some of this stuff, or come up with a more clever
solution, in future releases, but right let's keep it simple.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com