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From Nikolay Izhikov <nizhi...@apache.org>
Subject Re: New SQL execution engine
Date Fri, 27 Sep 2019 14:25:37 GMT
Igor.

> The main issue - there is no *selection*.

1. I don't remember community decision about this.

2. We should avoid to make such long-term decision so quickly.
We done this kind of decision with H2 and come to the point when we should review it.

> 1) Implementing white papers from scratch
> 2) Adopting Calcite to our needs.

The third option don't fix issues we have with H2.
The fourth option I know is using spark-catalyst.

What is wrong with writing engine from scratch?

I ask you to start with engine requirements.
Can we, please, discuss it?

> If you have an alternative - you're welcome, I'll gratefully listen to you.

We have alternative for now - H2 based engine.

> The main question isn't "WHAT" but "HOW" - that's the discussion topic from my point
of view.

When we make a decision about engine we can discuss roadmap for replacement.
One more time - replacement of SQL engine to some more customizable make sense for me.
But, this kind of decisions need carefull discussion.

В Пт, 27/09/2019 в 17:08 +0300, Seliverstov Igor пишет:
> Nikolay,
> 
> The main issue - there is no *selection*.
> 
> There is a field of knowledge - relational algebra, which describes how to transform
relational expressions saving their semantics, and a couple of implementations (Calcite is
only one written in Java).
> 
> There are only two alternatives:
> 
> 1) Implementing white papers from scratch
> 2) Adopting Calcite to our needs.
> 
> The second way was chosen by several other projects, there is experience, there is a
list of known issues (like using indexes) so, almost everything is already done for us.
> 
> Implementing a planner is a big deal, I think anybody understands it there. That's why
our proposal to reuse others experience is obvious.
> 
> If you have an alternative - you're welcome, I'll gratefully listen to you.
> 
> The main question isn't "WHAT" but "HOW" - that's the discussion topic from my point
of view.
> 
> Regards,
> Igor
> 
> > 27 сент. 2019 г., в 16:37, Nikolay Izhikov <nizhikov@apache.org> написал(а):
> > 
> > Roman.
> > 
> > > Nikolay, Maxim, I understand that our arguments may not be as obvious 
> > > for you as it obvious for SQL team. So, please arrange your questions in 
> > > a more constructive way.
> > 
> > What is SQL team?
> > I only know Ignite community :)
> > 
> > Please, share you knowledge in IEP.
> > I want to join to the process of engine *selection*.
> > It should start with the requirements to such engine.
> > Can you write it in IEP, please?
> > 
> > My point is very simple:
> > 
> > 1. We made the wrong decision with H2
> > 2. We should make a well-thought decision about the new engine.
> > 
> > > How many tickets would satisfy you?
> > 
> > You write about "issueS" with the H2.
> > All I see is one open ticket.
> > IEP doesn't provide enough information.
> > So it's not about the number of tickets, it's about
> > 
> > > These two points (single map-reduce execution and inflexible optimizer) 
> > > are the main problems with the current engine.
> > 
> > We may come to the point when Calcite(or any other engine) brings us third and other
"main problems".
> > This is how it happens with H2.
> > 
> > Let's start from what we want to get with the engine and move forward from this
base.
> > What do you think?
> > 
> > 
> > 
> > В Пт, 27/09/2019 в 16:15 +0300, Roman Kondakov пишет:
> > > Maxim, Nikolay,
> > > 
> > > I've listed two issues which show the ideological flaws of the current 
> > > engine.
> > > 
> > > 1. IGNITE-11448 - Open. This ticket describes the impossibility of 
> > > executing queries which can not be fit in the hardcoded one pass 
> > > map-reduce paradigm.
> > > 
> > > 2. IGNITE-6085 - Closed (won't fix) - This ticket describes the second 
> > > major problem with the current engine: H2 query optimizer is very 
> > > primitive and can not perform many useful optimizations.
> > > 
> > > These two points (single map-reduce execution and inflexible optimizer) 
> > > are the main problems with the current engine. It means that our engine 
> > > is currently  suitable for execution only a very limited subset of the 
> > > typical SQL queries. For example it can not even run most of the TPC-H 
> > > benchmark queries because they don't fit to the simple map-reduce paradigm.
> > > 
> > > > All I see is links to two tickets:
> > > 
> > > How many tickets would satisfy you? I named two. And it looks like it is 
> > > not enough from your point of view. Ok, so how many is enough? The set 
> > > of problems caused by listed above tickets is infinite, therefore I can 
> > > not create a ticket for each of them.
> > > > Tech details also should be added.
> > > 
> > > Tech details are in the tickets.
> > > 
> > > > We can't discuss such a huge change as an execution engine replacement
with descrition like:
> > > > "No data co-location control, i.e. arbitrary data can be returned silently"
or
> > > > "Low control on how query executes internally, as a result we have limited
possibility to implement improvements/fixes."
> > > 
> > > Why not? Don't you understand these problems? Or you don't think this is 
> > > a problem?
> > > 
> > > > Let's make these descriptions more specific.
> > > 
> > > What do you mean by "more specific"? What is the criteria of the 
> > > specific description?
> > > 
> > > 
> > > 
> > > Nikolay, Maxim, I understand that our arguments may not be as obvious 
> > > for you as it obvious for SQL team. So, please arrange your questions in 
> > > a more constructive way.
> > > 
> > > Thank you!
> 
> 

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