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From Andrey Gura <ag...@gridgain.com>
Subject Re: Transformers in SCAN queries
Date Fri, 05 Feb 2016 00:14:03 GMT
Val,

>From my point of view, special query class that allows transforming is
confusing. Two points about it:

1. ScanTransformQuery will duplicate ScanQuery code with all drawbacks that
we have. Moreover, any fix for ScanQuery should be repeated for
ScanTransformQuery. It will lead to bugs. DRY.

2. If some users want to do transformations for SqlQuery we will introduce
SqlTransformQuery. Right? At this point see previous item.

Transformation logic is some kind of strategy. IMHO, the most convenient
API should get transformation logic as some function provided by user.

On Thu, Feb 4, 2016 at 11:05 PM, Valentin Kulichenko <
valentin.kulichenko@gmail.com> wrote:

> Agree with Sergi. Mixing SQL with Java code transformers is confusing. In
> rare case when it's really required, user can implement a custom function.
>
> I copy-pasted the API to the ticket [1]. Please provide any additional
> comments there.
>
> [1] https://issues.apache.org/jira/browse/IGNITE-2546
>
> -Val
>
> On Thu, Feb 4, 2016 at 10:08 AM, Andrey Gura <agura@gridgain.com> wrote:
>
> > Sergi,
> >
> >
> > > What you are going to transform remotely here?
> >
> >
> > I'm not going. I believe :)
> >
> > Just hypothetical use case: You have one SqlFieldsQuery but different
> > requirements for returned values. For one case you have to return some
> > string fields as is and for another case you have to trim string to 32
> > characters. Of course you still can trim strings locally but transformers
> > allow you do it remotely.
> >
> > Anyway, this solution can be usefull for rest query types.
> >
> > On Thu, Feb 4, 2016 at 8:54 PM, Sergi Vladykin <sergi.vladykin@gmail.com
> >
> > wrote:
> >
> > > The whole point of Transformer is to do remote transform, how will this
> > > work with SqlFieldsQuery? What you are going to transform remotely
> here?
> > I
> > > believe all the transformations must happen at SQL level here.
> > >
> > > Sergi
> > >
> > >
> > >
> > > 2016-02-04 20:10 GMT+03:00 Andrey Gura <agura@gridgain.com>:
> > >
> > > > SqlQuery, TextQuery and SpiQuery are similar to ScanQuery because all
> > of
> > > > them also defined as Query<Cache.Entry<>>.
> > > >
> > > > It can be usefull to have one query SqlQuery that can return
> different
> > > > result that will be produced from cache entry by transformer.
> > > >
> > > > Actually only SqlFieldsQuery has different definition. So
> transformers
> > > can
> > > > be applied to any type of query (including SqlFieldsQuery, I
> believe).
> > > >
> > > > On Thu, Feb 4, 2016 at 7:42 PM, Sergi Vladykin <
> > sergi.vladykin@gmail.com
> > > >
> > > > wrote:
> > > >
> > > > > I don't like the idea of having additional method *query(Query<E>
> > qry,
> > > > > Transformer<E, R> transfomer); *because I don't see how these
> > > > transformers
> > > > > will work for example with SQL, but this API makes you think that
> > > > > transformers are supported for all the query types.
> > > > >
> > > > > Sergi
> > > > >
> > > > > 2016-02-04 16:46 GMT+03:00 Andrey Gura <agura@gridgain.com>:
> > > > >
> > > > > > Val,
> > > > > >
> > > > > > can we introduce new method into IgnteCache API?
> > > > > >
> > > > > > Now we have method: public <R> QueryCursor<R> query(Query<R>
> qry);
> > > > > >
> > > > > > New method will be something like this: <R> QueryCursor<R>
> > > > query(Query<E>
> > > > > > qry, Transformer<E, R> transfomer);
> > > > > >
> > > > > > It allows provide transformers for all query types and chnages
> will
> > > be
> > > > > > related only with query cursor functionality.
> > > > > >
> > > > > > Will it work?
> > > > > >
> > > > > > On Thu, Feb 4, 2016 at 11:13 AM, Andrey Kornev <
> > > > andrewkornev@hotmail.com
> > > > > >
> > > > > > wrote:
> > > > > >
> > > > > > > Another perhaps bigger problem with running queries (including
> > scan
> > > > > > > queries) using closures was discussed at length on the
@dev not
> > so
> > > > long
> > > > > > > ago. It has to do with partitions migration due to cluster
> > topology
> > > > > > changes
> > > > > > > which may result in the query returning incomplete result.
And
> > > while
> > > > it
> > > > > > is
> > > > > > > possible to solve this problem for the scan queries by
using
> some
> > > > > clever
> > > > > > > tricks, all bets are off with the SQL queries.Andrey
> > > > > > >     _____________________________
> > > > > > > From: Valentin Kulichenko <valentin.kulichenko@gmail.com>
> > > > > > > Sent: Thursday, February 4, 2016 6:29 AM
> > > > > > > Subject: Re: Transformers in SCAN queries
> > > > > > > To:  <dev@ignite.apache.org>
> > > > > > >
> > > > > > >
> > > > > > >                    Dmitry,
> > > > > > >
> > > > > > >  The main difference in my view is that you lose pagination
> when
> > > > > sending
> > > > > > >  results from servers to client. What if one wants to iterate
> > > through
> > > > > all
> > > > > > >  entries in cache?
> > > > > > >
> > > > > > >  On Wed, Feb 3, 2016 at 9:47 PM, Dmitriy Setrakyan <
> > > > > > dsetrakyan@apache.org>
> > > > > > >  wrote:
> > > > > > >
> > > > > > >  > Valentin,
> > > > > > >  >
> > > > > > >  > Wouldn’t the same effect be achieved by broadcasting
a
> closure
> > > to
> > > > > the
> > > > > > >  > cluster and executing scan-query on every node locally?
> > > > > > >  >
> > > > > > >  > D.
> > > > > > >  >
> > > > > > >  > On Wed, Feb 3, 2016 at 9:17 PM, Valentin Kulichenko
<
> > > > > > >  > valentin.kulichenko@gmail.com> wrote:
> > > > > > >  >
> > > > > > >  > > Igniters,
> > > > > > >  > >
> > > > > > >  > > I keep getting requests from our users to add
optional
> > > > > transformers
> > > > > > to
> > > > > > >  > SCAN
> > > > > > >  > > queries. This will allow to iterate through
cache, but do
> > not
> > > > > > transfer
> > > > > > >  > > whole key-value pairs across networks (e.g.,
get only
> keys).
> > > The
> > > > > > > feature
> > > > > > >  > > looks useful and I created a ticket [1].
> > > > > > >  > >
> > > > > > >  > > I am struggling with the design now. The problem
is that I
> > > > wanted
> > > > > to
> > > > > > >  > extend
> > > > > > >  > > existing ScanQuery object for this, but this
seems to be
> > > > > impossible
> > > > > > >  > because
> > > > > > >  > > it already extends Query<Cache.Entry<K,
V>> and thus can
> > > iterate
> > > > > > only
> > > > > > >  > > through entries.
> > > > > > >  > >
> > > > > > >  > > The only option I see now is to create a separate
query
> > type,
> > > > > > > copy-paste
> > > > > > >  > > everything from ScanQuery and add *mandatory*
transformer.
> > > > > Something
> > > > > > > like
> > > > > > >  > > this:
> > > > > > >  > >
> > > > > > >  > > ScanTransformQuery<K, V, R> extends Query<R>
{
> > > > > > >  > >     IgniteBiPredicate<K, V> filter;
> > > > > > >  > >     IgniteClosure<Cache.Entry<K, V>,
R> transformer;
> > > > > > >  > >     int part;
> > > > > > >  > >     ...
> > > > > > >  > > }
> > > > > > >  > >
> > > > > > >  > > Thoughts? Does anyone has other ideas?
> > > > > > >  > >
> > > > > > >  > > [1]    https://issues.apache.org/jira/browse/IGNITE-2546
> > > > > > >  > >
> > > > > > >  > > -Val
> > > > > > >  > >
> > > > > > >  >
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > --
> > > > > > Andrey Gura
> > > > > > GridGain Systems, Inc.
> > > > > > www.gridgain.com
> > > > > >
> > > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Andrey Gura
> > > > GridGain Systems, Inc.
> > > > www.gridgain.com
> > > >
> > >
> >
> >
> >
> > --
> > Andrey Gura
> > GridGain Systems, Inc.
> > www.gridgain.com
> >
>



-- 
Andrey Gura
GridGain Systems, Inc.
www.gridgain.com

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