Re: Partial vacuum versus pg_class.reltuples

On Mon, Jun 8, 2009 at 10:40 AM, Alvaro
Herrera<alvherre(at)commandprompt(dot)com> wrote:
> Tom Lane escribió:
>> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
>> > Robert Haas escribió:
>> >> Maybe we should just have a GUC to enable/disable
>> >> partial vacuums.
>>
>> > IIRC you can set vacuum_freeze_table_age to 0.
>>
>> That has the same effects as issuing VACUUM FREEZE, no?
>
> As far as I can make from the docs, I think it only forces a full table
> scan, but the freeze age remains the same.

Yeah, that looks like what I was looking for, thanks. I looked for it
in the docs under the vacuum-related sections, but couldn't find it,
and I didn't know the name of it so I couldn't find it that way
either. I wonder if we should consider moving all of the vacuum and
autovacuum parameters into one section.

http://developer.postgresql.org/pgdocs/postgres/runtime-config-client.html#GUC-VACUUM-FREEZE-TABLE-AGE

In the worst case scenario where the new partial-table-vacuums are
causing headaches for someone, they should hopefully be able to use
this parameter to basically turn them off without too many nasty side
effects.

(Another nice thing about this parameter is that if you have a really
big table that is append-mostly, you can potentially tune this
parameter downward to spread out the freezing activity. With the
default settings, you might cruise along merrily until you hit 150M
transactions and then generate an I/O storm as you freeze a pretty big
chunk of the table all at once. With a lower setting, non-partial
vacuums will be more frequent, but each one will generate a smaller
amount of write traffic.)

...Robert