Re: Horizontal scalability/sharding

On 30 August 2015 at 03:17, Bruce Momjian <bruce(at)momjian(dot)us> wrote:

> I have recently increased my public statements about the idea of adding
> horizontal scaling/sharding to Postgres.

Glad to see it. Many people have been pushing such things for years, so it
is good to finally see some debate about this on Hackers.

> I wanted to share with hackers
> a timeline of how we got here, and where I think we are going in the
> short term:
>
> 2012-2013: As part of writing my scaling talk
> (http://momjian.us/main/presentations/overview.html#scaling), studying
> Oracle RAC, and talking to users, it became clear that an XC-like
> architecture (sharding) was the only architecture that was going to allow
> for write scaling.
>

What other architectures were discussed? Where was that discussion?

> Users and conference attendees I talked to were increasingly concerned
> about the ability of Postgres to scale for high write volumes. They didn't
> necessarily need that scale now, but they needed to know they could get
> it if they wanted it, and wouldn't need to switch to a new database in
> the future. This is similar to wanting a car that can get you on a highway
> on-ramp fast --- even if you don't need it, you want to know it is there.
>

+1

> 2014: I started to shop around the idea that we could use FDWs,
> parallelism, and a transaction/snapshot manager to get XC features
> as built-in to Postgres. (I don't remember where the original idea
> came from.) It was clear that having separate forks of the source code
> in XC and XL was never going to achieve critical mass --- there just
> aren't enough people who need high right scale right now, and the fork
> maintenance overhead is a huge burden.
>

I personally support the view that we should put scalability features into
Postgres core, rather than run separate forks.

> I realized that we would never get community acceptance to dump the XC
> (or XL) code needed for sharding into community Postgres

How or why did you realize that? There has never been any such discussion,
AFAIK. Surely it can be possible to move required subsystems across?

> , but with FDWs,
> we could add the features as _part_ of improving FDWs, which would benefit
> FDWs _and_ would be useful for sharding. (We already see some of those
> FDW features in 9.5.)
>

That is a huge presumption. Not discussed or technically analyzed in any
way with the community.

> October, 2014: EDB and NTT started working together in the community
> to start improving FDWs as a basis for an FDW-based sharding solution.
> Many of the 9.5 FDW improvements that also benefit sharding were developed
> by a combined EDB/NTT team. The features improved FDWs independent of
> sharding, so they didn't need community buy-in on sharding to get them
> accepted.
>
> June, 2015: I attended the PGCon sharding unconference session and
> there was a huge discussion about where we should go with sharding.
> I think the big take-away was that most people liked the FDW approach,
> but had business/customer reasons for wanting to work on XC or XL because
> those would be production-ready faster.
>

Cough, cough. You must surely be joking that "most people liked the FDW
approach"? How did we measure the acceptance of this approach?

What actually is the FDW approach? Since its not been written down
anywhere, or even explained verbally, how can anyone actually agree to it?

> July, 2015: Oleg Bartunov and his new company Postgres Professional (PP)
> started to think about joining the FDW approach, rather than working on
> XL, as they had stated at PGCon in June. A joint NTT/EDB/PP phone-in
> meeting is scheduled for September 1.
>

> August, 2015: While speaking at SFPUG, Citus Data approached me about
> joining the FDW sharding team. They have been invited to the September
> 1 meeting, as have the XC and XL people.
>

2ndQuadrant is working in this area, specifically bringing XL 9.5 forwards.
Please can invites be posted to myself, Pavan Deolasee and Petr Jelinek
also? I'll pass on to others also.

Koichi Suzuki is arranging a meeting in Hong Long for XC/XL discussions.
Presumably EDB is invited also? If Koichi is a leading organizer of this,
why are there two meetings?

October, 2015: EDB is sponsoring a free 3-hour summit about FDW sharding
> at the PG-EU conference in Vienna. Everyone is invited, but it is hoped
> most of the September 1 folks can attend.
>

> February, 2016: Oleg is planning a similar meeting at their February
> Moscow conference.
>

> Anyway, I wanted to explain the work that has been happening around
> sharding.

Thanks

> As things move forward, I am increasingly convinced that write
> scaling will be needed soon,

+1

> that the XC approach is the only reasonable way to do it,

> and that FDWs are the cleanest way to get it into community
> Postgres.
>

Those two things aren't at all obvious to me.

Please don't presume my opposition. If the technical information were made
public, I might understand and agree with "the FDW approach", perhaps
others also. 2ndQuadrant is certainly happy to become involved in any team
aiming to add features to Postgres core, as long as that makes sense. There
may be areas we can all agree upon even if the full architecture remains in
doubt.

Before the community commits to a long term venture together we should see
the plan. Like all IT projects, expensive failure is possible and the lack
of a design is a huge flashing red warning light for me at present. If that
requires a meeting of all Developers, why are the meetings for this
specifically not happening at the agreed Developer meetings?

--
Simon Riggs http://www.2ndQuadrant.com/
<http://www.2ndquadrant.com/>
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