Re: Protecting against unexpected zero-pages: proposal

Robert,

> Uh, no it doesn't.  It only requires you to be more aggressive about
> vacuuming the transactions that are in the aborted-XIDs array.  It
> doesn't affect transaction wraparound vacuuming at all, either
> positively or negatively.  You still have to freeze xmins before they
> flip from being in the past to being in the future, but that's it.

Sorry, I was trying to say that it's similar to the freeze issue, not
that it affects freeze.  Sorry for the lack of clarity.

What I was getting at is that this could cause us to vacuum
relations/pages which would otherwise never be vaccuumed (or at least,
not until freeze).  Imagine a very large DW table which is normally
insert-only and seldom queried, but once a month or so the insert aborts
and rolls back.

I'm not saying that your proposal isn't worth testing.  I'm just saying
that it may prove to be a net loss to overall system efficiency.

>> If we ever handle that, would #6 be a moot point, or do you think
>> > it's still a significant issue?

Kevin, the case which your solution doesn't fix is the common one of
"log tables" which keep adding records continuously, with < 5% inserts
or updates.  That may seem like a "corner case" but such a table,
partitioned or unpartitioned, exists in around 1/3 of the commercial
applications I've worked on, so it's a common pattern.

--                                  -- Josh Berkus                                    PostgreSQL Experts Inc.
                        http://www.pgexperts.com