On Wed, Jan 30, 2013 at 5:39 AM, Kevin Grittner <kgrittn(at)ymail(dot)com> wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
>> Don't think I did. I was talking about vacuum_freeze_table_age
>> because that influences the amount of full-table scans
> Not any more than vacuum_freeze_min_age does.
There is a lot more room for vacuum_freeze_table_age to be increased,
then there is for vacuum_freeze_min_age to be decreased.
> | a whole table sweep is forced if the table hasn't been fully
> | scanned for vacuum_freeze_table_age minus vacuum_freeze_min_age
> | transactions.
Why is vacuuming described as such a violent process? It doesn't
"force" a table sweep, it just goes ahead and performs one. In
general, it seems hard to tell from the docs that this only promotes a
vacuum which is going to happen anyway from a vm one to a full scan
one. The forcefulness makes it sound more like it is doing vacuums
that wouldn't happen otherwise (like autovacuum_freeze_max_age does,
which actually could be described as "force" since it turns on the
autovac launcher even if it is configured to be off)
> So reducing vacuum_freeze_min_age not only helps minimize the
> writes that are needed when autovacuum needs to scan the entire
How does it do that? If the tuple doesn't need to frozen now because
it was already frozen, that just means the write happened at a
different time but it still happened.
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