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 <andrewkor...@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.kuliche...@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 <dsetrak...@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.kuliche...@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
