Re: Why do we let autovacuum give up?

On Thu, Jan 23, 2014 at 1:41 PM, Mark Kirkwood <
mark(dot)kirkwood(at)catalyst(dot)net(dot)nz> wrote:

> On 24/01/14 10:16, Mark Kirkwood wrote:
>
>> On 24/01/14 10:09, Robert Haas wrote:
>>
>>> On Thu, Jan 23, 2014 at 4:03 PM, Mark Kirkwood
>>> <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz> wrote:
>>>
>>>> On 24/01/14 09:49, Tom Lane wrote:
>>>>
>>>>> 2. What have you got that is requesting exclusive lock on pg_attribute?
>>>>> That seems like a pretty unfriendly behavior in itself. regards, tom
>>>>> lane
>>>>>
>>>> I've seen this sort of problem where every db session was busily
>>>> creating
>>>> temporary tables. I never got to the find *why* they needed to make so
>>>> many,
>>>> but it seemed like a bad idea.
>>>>
>>> But... how does that result on a vacuum-incompatible lock request
>>> against pg_attribute?
>>>
>>> I see that it'll insert lots of rows into pg_attribute, and maybe
>>> later delete them, but none of that blocks vacuum.
>>>
>>>
>> That was my thought too - if I see it happening again here (was a year or
>> so ago that I saw some serious pg_attribute bloat) I'll dig deeper.
>>
>>
>>
> Actually not much digging required. Running the attached script via
> pgbench (8 sessions) against a default configured postgres 8.4 sees
> pg_attribute get to 1G after about 15 minutes.
>

At that rate, with default throttling, it will be a close race whether
autovac can vacuum pages as fast as they are being added. Even if it never
gets cancelled, it might not ever finish.

Cheers,

Jeff