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Re: autovacuum not prioritising for-wraparound tables

From: Christopher Browne <cbbrowne(at)gmail(dot)com>
To: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: autovacuum not prioritising for-wraparound tables
Date: 2013-01-31 20:28:58
Message-ID: CAFNqd5UpzusNfHD=xmduosuBh94nxie2y33=2wQ0iL4gm6A76A@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, Jan 31, 2013 at 3:18 PM, Alvaro Herrera
<alvherre(at)2ndquadrant(dot)com> wrote:
> Robert Haas escribió:
>> On Thu, Jan 31, 2013 at 2:40 PM, Alvaro Herrera
>> <alvherre(at)2ndquadrant(dot)com> wrote:
>> > Alvaro Herrera escribió:
>> >
>> >> Okay, here's a patch along these lines.  I haven't considered Jim's
>> >> suggestion downthread about discounting dead tuples from relpages; maybe
>> >> we can do that by subtracting the pages attributed to dead ones,
>> >> estimating via tuple density (reltuples/relpages).
>> >
>> > Patch attached.
>>
>> This strikes me as too clever by half.  You've introduced the concept
>> of a "Browne strength" (apparently named for Christopher Browne) and
>> yet you haven't even bothered to add a comment explaining the meaning
>> of the term, let along justifying the choice of that formula rather
>> than any other.  I don't want to dog this proposal to death, because
>> surely we can do better than the status quo here, but adopting the
>> first formula someone proposed without any analysis of whether it does
>> the right thing cannot possibly be the correct decision process.
>
> My intention was to apply a Nasby correction to Browne Strength and call
> the resulting function Browne' (Browne prime).  Does that sound better?
>
> Now seriously, I did experiment a bit with this and it seems to behave
> reasonably.  Of course, there might be problems with it, and I don't
> oppose to changing the name.  "Vacuum strength" didn't sound so great,
> so I picked the first term that came to mind.  It's not like picking
> people's last names to name stuff is a completely new idea; that said,
> it was sort of a joke.

Color me amused :-).

And, when thinking about how strong these things are, just remember,
"smell isn't everything".

I spent 20 minutes at a whiteboard arriving at the "Browne strength",
and I think it's not unreasonable as a usage of the data already
immediately at hand.  But it is absolutely just intended as a
strawman proposal, and I'd be pleased to see it get prodded into
something more "prime."
-- 
When confronted by a difficult problem, solve it by reducing it to the
question, "How would the Lone Ranger handle this?"


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