Re: limiting hint bit I/O

> If the problem is that all the freezing happens at once, then ISTM the
> solution is to add a random factor. Say, when a tuple just passes the
> lower threshold it has a 1% chance of being frozen. The chance grows
> until it is 100% as it reaches the upper threshold.

Doesn't have to be random; it could be determinative.  That is, we could
have a vacuum_freeze_max_size parameter ... and accompanying autovacuum
parameter ... which allowed the user to limit freezing scans to, say,
1GB of the table at a time.  If I could, say, call a manual freeze of
10% of the largest tables ever night, then I might actually be able to
schedule it.  It's a full scan of the whole table which is fatal.

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