Re: truncating pg_multixact/members

On 2014-01-06 20:51:57 -0500, Robert Haas wrote:
> On Mon, Jan 6, 2014 at 7:50 PM, Jim Nasby <jim(at)nasby(dot)net> wrote:
> > On 1/4/14, 8:19 AM, Robert Haas wrote:
> >> Also, while multixactid_freeze_min_age should be low, perhaps a
> >> million as you suggest, multixactid_freeze_table_age should NOT be
> >> lowered to 3 million or anything like it. If you do that, people who
> >> are actually doing lots of row locking will start getting many more
> >> full-table scans. We want to avoid that at all cost. I'd probably
> >> make the default the same as for vacuum_freeze_table_age, so that
> >> mxids only cause extra full-table scans if they're being used more
> >> quickly than xids.
> >
> > Same default as vacuum_freeze_table_age, or default TO
> > vacuum_freeze_table_age? I'm thinking the latter makes more sense...
>
> Same default. I think it's a mistake to keep leading people to think
> that the sensible values for one set of parameters are somehow related
> to a sensible set of values for the other set. They're really quite
> different things.

Valid argument - on the other hand, defaulting to the current variable's
value has the advantage of being less likely to cause pain when doing a
minor version upgrade because suddenly full table vacuums are much more
frequent.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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