Re: Improve the concurency of vacuum full table and select statement on the same relation

On 10/16/15 10:04 AM, Robert Haas wrote:
> On Thu, Oct 15, 2015 at 8:28 PM, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com> wrote:
>> It's just how the authors of pg_repack decided to handle it. It seems pretty
>> reasonable, since you probably don't want an errant DDL statement to cause
>> the rollback of hours or days of pg_repack work.
>>
>> Ultimately, I don't think you'll find many people interested in working on
>> this, because the whole goal is to never need VACUUM FULL or pg_repack. If
>> you're clustering just for the sake of clustering, that has it's own set of
>> difficulties that should be addressed.
>
> I think the topic of online table reorganization is a pretty important
> one, actually. That is a need that we have had for a long time,
> creates serious operational problems for users, and it's also a need
> that is not going away. I think the chances of eliminating that need
> completely, even if we rearchitected or heap storage, are nil.

Yeah, which is why I made the comment about CLUSTER.

> I think the bigger issue is that it's a very hard problem to solve.

ISTM nothing can be done here until there's some way to influence how
pages get pulled from the FSM (IE: pull from one of the first X pages
with free space). Maybe having some way to expose that would be enough
of a start.

> pg_repack is one approach, but I've heard more than one person say
> that, as C-3PO said about the asteroid, it may not be entirely stable.

I looked at it recently, and it seems to be under active development.
But I agree it'd be better if we could handle this internally.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com