ignite-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Vladimir Ozerov <voze...@gridgain.com>
Subject Re: Resurrect FairAffinityFunction
Date Wed, 16 Aug 2017 05:41:08 GMT
Dima,

It is not hard to implement. It is hard to reason on whether your query
will fail or not. Moreover, cache groups is an antipattern for SQL,
personally I do not want users to use it unless absolutely needed (large
topologies, large number of caches). Also take in count that the same
problem with different partition distribution holds for any two caches with
different affinity functions, so the problem is not tied to
FairAffinityFunction only.

IMO correct fix should be as follows:
1) Add requirement that every affinity function must provide sensible
implementation of equals/hashCode
2) Add "boolean deterministic()" method to affinity function interface;
"true" means that function doesn't depend on any external things, such as
topology history
3) Fail SQL if there are at least two PARTITIONED caches with different or
non-deterministic affinity functions, and distributed joins are not enabled
4) Fix FairAffinityFunction and make it deterministic, it should not depend
on previous state.

Makes sense?

On Wed, Aug 16, 2017 at 3:31 AM, Dmitriy Setrakyan <dsetrakyan@apache.org>
wrote:

> On Tue, Aug 15, 2017 at 1:12 PM, Vladimir Ozerov <vozerov@gridgain.com>
> wrote:
>
> > I do not like the idea as it would make it very hard to reason about
> > whether your SQL will fail or not. Let's looks at the problem from the
> > different angle. I have this question for years - why in the world *fair*
> > affinity function, whose only ultimate goal is to provide equal partition
> > distribution, depends on it's own previous state? Can we re-design in a
> way
> > that it depends only on partition count and current topology state?
> >
>
> Vladimir, we must know previous state, otherwise the data partitions will
> be randomly moving across the network every time a topology changes.
>
> From the SQL standpoint, you can just fail all queries that have a JOIN
> from different cache groups, if at least one of the groups is using Fair
> Affinity. I am not sure why this would be hard.
>
>
> >
> > On Thu, Aug 10, 2017 at 12:16 AM, Valentin Kulichenko <
> > valentin.kulichenko@gmail.com> wrote:
> >
> > > As far as I know, all logical caches with the same affinity function
> and
> > > node filter will end up in the same group. If that's the case, I like
> the
> > > idea. This is exactly what I was looking for.
> > >
> > > -Val
> > >
> > > On Wed, Aug 9, 2017 at 8:18 AM, Evgenii Zhuravlev <
> > > e.zhuravlev.wk@gmail.com>
> > > wrote:
> > >
> > > > Dmitriy,
> > > >
> > > > Yes, you're right. Moreover, it looks like a good practice to combine
> > > > caches that will be used for collocated JOINs in one group since it
> > > reduces
> > > > overall overhead.
> > > >
> > > > I think it's not a problem to add this restriction to the SQL JOIN
> > level
> > > if
> > > > we will decide to use this solution.
> > > >
> > > > Evgenii
> > > >
> > > >
> > > >
> > > >
> > > > 2017-08-09 17:07 GMT+03:00 Dmitriy Setrakyan <dsetrakyan@apache.org
> >:
> > > >
> > > > > On Wed, Aug 9, 2017 at 6:28 AM, ezhuravl <e.zhuravlev.wk@gmail.com
> >
> > > > wrote:
> > > > >
> > > > > > Folks,
> > > > > >
> > > > > > I've started working on a https://issues.apache.org/
> > > > > > jira/browse/IGNITE-5836
> > > > > > ticket and found that the recently added feature with cacheGroups
> > > doing
> > > > > > pretty much the same that was described in this issue. CacheGroup
> > > > > > guarantees
> > > > > > that all caches within a group have same assignments since they
> > > share a
> > > > > > single underlying 'physical' cache.
> > > > > >
> > > > >
> > > > > > I think we can return FairAffinityFunction and add information
to
> > its
> > > > > > Javadoc that all caches with same AffinityFunction and NodeFilter
> > > > should
> > > > > be
> > > > > > combined in cache group to avoid a problem with inconsistent
> > previous
> > > > > > assignments.
> > > > > >
> > > > > > What do you guys think?
> > > > > >
> > > > >
> > > > > Are you suggesting that we can only reuse the same
> > FairAffinityFunction
> > > > > across the logical caches within the same group? This would mean
> that
> > > > > caches from the different groups cannot participate in JOINs or
> > > > collocated
> > > > > compute.
> > > > >
> > > > > I think I like the idea, however, we need to make sure that we
> > enforce
> > > > this
> > > > > restriction, at least at the SQL JOIN level.
> > > > >
> > > > > Alexey G, Val, would be nice to hear your thoughts on this.
> > > > >
> > > > >
> > > > > >
> > > > > > Evgenii
> > > > > >
> > > > > >
> > > > > >
> > > > > > --
> > > > > > View this message in context: http://apache-ignite-
> > > > > > developers.2346864.n4.nabble.com/Resurrect-FairAffinityFunction-
> > > > > > tp19987p20669.html
> > > > > > Sent from the Apache Ignite Developers mailing list archive
at
> > > > > Nabble.com.
> > > > > >
> > > > >
> > > >
> > >
> >
>

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message