| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, PostgreSQL-Dev <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Vacuum: allow usage of more than 1GB of work mem |
| Date: | 2016-09-06 18:51:14 |
| Message-ID: | CANP8+j+rHpWYw4gOvxmE5hM8jx4ASgi=nWufBb0MqiD=MfVA-w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 6 September 2016 at 19:23, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Tue, Sep 6, 2016 at 2:16 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> What occurs to me is that we can exactly predict how many tuples we
>> are going to get when we autovacuum, since we measure that and we know
>> what the number is when we trigger it.
>>
>> So there doesn't need to be any guessing going on at all, nor do we
>> need it to be flexible.
>
> No, that's not really true. A lot can change between the time it's
> triggered and the time it happens, or even while it's happening.
> Somebody can run a gigantic bulk delete just after we start the
> VACUUM.
Which wouldn't be removed by the VACUUM, so can be ignored.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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