Re: Freezing without write I/O

On 31.05.2013 00:06, Bruce Momjian wrote:
> On Thu, May 30, 2013 at 04:33:50PM +0300, Heikki Linnakangas wrote:
>> This would also be the first step in allowing the clog to grow
>> larger than 2 billion transactions, eliminating the need for
>> anti-wraparound freezing altogether. You'd still want to truncate
>> the clog eventually, but it would be nice to not be pressed against
>> the wall with "run vacuum freeze now, or the system will shut down".
>
> Keep in mind that autovacuum_freeze_max_age is 200M to allow faster clog
> truncation. Does this help that?

No. If you want to keep autovacuum_freeze_max_age set at less than 2
billion, you don't need support for more than 2 billion transactions.
But for those who would like to set autovacuum_freeze_max_age higher
than 2B, it would be nice to allow it.

Actually, even with autovacuum_freeze_max_age = 200 M, it would be nice
to not have the hard stop at 2 billion, in case autovacuum falls behind
really badly. With autovacuum_freeze_max_age = 200M, there's a lot of
safety margin, but with 1000M or so, not so much.

- Heikki