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From Alexey Goncharuk <alexey.goncha...@gmail.com>
Subject Re: Default hash code generation strategy for new binary objects
Date Thu, 29 Sep 2016 16:19:05 GMT
I want to step back a little bit. Why do we need to choose fields for
hashCode at all? If all fields participate in equals, all of them should
participate in hashCode as well. We already serialize a user key in order
to get a value from cache, so we can use a hashCode based on binary object
representation.

2016-09-29 19:13 GMT+03:00 Dmitriy Setrakyan <dsetrakyan@apache.org>:

> Alexander,
>
> How do you plan to annotate fields that participate in the hashcode
> calculation? Can you add all the changes you plan to make to the
> configuration in the ticket and post the link here?
>
> Also, we must make sure that hashcode fields do not change. I believe you
> should have validation in the code on startup of a system or of a cache,
> and throw an exception if it fails.
>
> D.
>
> On Thu, Sep 29, 2016 at 9:08 AM, Alexander Paschenko <
> alexander.a.paschenko@gmail.com> wrote:
>
> > Thanks everyone!
> >
> > Denis, yes, that's what I meant, now we're on the same page :)
> > However, I'm worried about the same things Alexey is, that is, I'm not
> > sure how we can handle presence of key fields that don't participate
> > in 'equals' evaluation. Hence I'm all up for keeping mechanism of
> > comparison for equality as it is now. And simply enhance the
> > configuration as follows:
> >
> > 1. Introduce new BinaryObjectHashCodeResolver interface with single
> > method having following signature:
> >
> > int computeHashCode(BinaryObject binObj)
> >
> > Cache configuration will then get a new corresponding param - probably
> > a class/class name to instantiate resolver from.
> >
> > 2. Introduce default resolver by enhancing SQL engine configuration (=
> > QueryEntity) - namely, add to it the list of hash code fields and
> > optional affinity key field.
> >
> >
> >
> > 2016-09-29 18:39 GMT+03:00 Alexey Goncharuk <alexey.goncharuk@gmail.com
> >:
> > > Folks, let me point out a few obvious (or not) things
> > >
> > > A set of fields participating in hashCode and equals is impossible to
> > > change without cluster restart. Imagine a new client adding a field F
> to
> > > key structure (A, B) so that new key is (A, B, F). In this case key (1,
> > 2,
> > > 0) will be treated as a different key w/respect to (1, 2, 3), while the
> > new
> > > client expects them to be the same. I think the set of fields defining
> > the
> > > key _must_ be used in both hash code and equals calculation and cannot
> > > change over time. Having said that, we can use binary array comparison
> as
> > > object equality test. Presence of new 'garbage' fields in key looks
> > useless
> > > to me.
> > >
> > > So, we should support:
> > > 1) All the things Dmitriy pointed out, in other words - multi-field key
> > > with affinity key fields
> > > 2) Ability to instantiate the key using a text-only environment
> > > 3) Ability to define the structure of a key using XML or DDL
> > >
> > > I think all of these can be done via combination of HashCodeResolver
> > > interface + default resolver which can read type configuration.
> > >
> > > 2016-09-29 3:54 GMT+03:00 Dmitriy Setrakyan <dsetrakyan@apache.org>:
> > >
> > >> Guys,
> > >>
> > >> We need to look at 3 cases:
> > >>
> > >> a) key is just one field
> > >> b) key is multiple fields
> > >> c) key is one or multiple fields, with possibility of an alternate
> > affinity
> > >> key
> > >>
> > >> For (a) and (b), whenever a type is defined in XML, and further in
> DML,
> > a
> > >> user will specify which fields are part of the key. In that case, we
> > should
> > >> just grab those fields and calculate the hashcode automatically.
> > >>
> > >> For (c), a user should specify in XML, and further in DML, which
> fields
> > >> should be used for affinity, in addition to the key fields. In that
> > case,
> > >> we again should grab those fields and calculate the hashcodes for the
> > >> primary key and the affinity key.
> > >>
> > >> I really am not sure if there are other ways of doing it. Am I missing
> > >> something?
> > >>
> > >> D.
> > >>
> > >>
> > >> On Wed, Sep 28, 2016 at 5:14 PM, Denis Magda <dmagda@gridgain.com>
> > wrote:
> > >>
> > >> > Let me show the picture I have in my mind:
> > >> >
> > >> > Primary key is a must for all INSERT and MERGE operations. If it’s
> not
> > >> set
> > >> > then an INSERT/MERGE fails.
> > >> > If a primary key is a boxed/unboxed primitive (int, Integer, String,
> > >> Date,
> > >> > etc.) then the key value is used for hashCode calculation. At the
> same
> > >> time
> > >> > the key will be an affinity key.
> > >> > If a primary key is a custom object then it’s value can be passed
> as a
> > >> > param directly from Java, .Net, C++ in a way like “INSERT (_key,
> > field1,
> > >> > field2) VALUES (?, val1, val2)”. In this scenario we will call
> > hashCode
> > >> > directly on the key's value. In addition, we will be able to get an
> > >> > affinity key since we know key’s type class descriptor
> > >> > (BinaryClassDescriptor).
> > >> > If a primary key is still a custom key and we want to insert its
> value
> > >> > from an SQL console, PHP, Tableu, etc. then we can’t pass the key’s
> > value
> > >> > as is. Here we’re trying to apply a workaround by listing key's
> > fields in
> > >> > INSERT/MERGE and the task is to properly re-construct the key on our
> > side
> > >> > using only specific fields.
> > >> >
> > >> > Is my understanding correct for all the bullets above?
> > >> >
> > >> > If so then, yes, I would agree that we need to list these fields in
> a
> > >> > configuration and the default hash code resolver will use them as
> > well.
> > >> > Moreover, we have to pin point an affinity field. So, the question
> is
> > >> what
> > >> > the configuration we should use.
> > >> >
> > >> > Community, any other thoughts/ideas?
> > >> >
> > >> > —
> > >> > Denis
> > >> >
> > >> > > On Sep 28, 2016, at 4:16 PM, Alexander Paschenko <
> > >> > alexander.a.paschenko@gmail.com> wrote:
> > >> > >
> > >> > > Also MERGE.
> > >> > >
> > >> > > 2016-09-29 2:10 GMT+03:00 Denis Magda <dmagda@gridgain.com>:
> > >> > >> You need a hash code only for INSERT operation, right?
> > >> > >>
> > >> > >> —
> > >> > >> Denis
> > >> > >>
> > >> > >>> On Sep 28, 2016, at 3:47 PM, Alexander Paschenko <
> > >> > alexander.a.paschenko@gmail.com> wrote:
> > >> > >>>
> > >> > >>> But what if the user works from some kind of console
and just
> > types
> > >> > >>> the queries as text in full and does not bind params
via JDBC or
> > >> > >>> something alike? What if there's no binary object? I
don't see
> > why we
> > >> > >>> should keep the user from usual cache gets in this case.
I
> really
> > >> like
> > >> > >>> the idea of supplying the values of distinct fields,
thus
> freeing
> > the
> > >> > >>> user of the need to mess with objects and builders, AND
then
> just
> > >> > >>> calculating hash code as suggested before - say, via
explicitly
> > >> > >>> listing participating fields in XML or by marking them
with
> > transient
> > >> > >>> keyword or some annotation.
> > >> > >>> Actually, I believe that's the only case when we need
to
> generate
> > any
> > >> > >>> hash codes - when the class is present, we can just get
hash
> code
> > >> from
> > >> > >>> its implementation of its method. When there's no class,
we
> > generate.
> > >> > >>> And all that is solely for SQL. For the rest - just throw
an
> > >> exception
> > >> > >>> when there's no hash code manually set for binary object.
I
> don't
> > see
> > >> > >>> why we should try to generate anything when the user
already is
> > using
> > >> > >>> Ignite in full, not just via limited interface of SQL.
> > >> > >>>
> > >> > >>> 2016-09-29 0:31 GMT+03:00 Denis Magda <dmagda@gridgain.com>:
> > >> > >>>> Hmm, this is a good question.
> > >> > >>>>
> > >> > >>>> If a user doesn’t provide a _key when an INSERT
is executed for
> > me
> > >> it
> > >> > means that he is not going to use the key later for cache.get/put,
> > >> DELETE,
> > >> > UPDATE and other possible operation simply because he doesn’t know
> > how to
> > >> > reconstruct the key back in his code. If he wants to use the primary
> > key
> > >> in
> > >> > the rest of operations then he must provide it at INSERT time.
> > >> > >>>>
> > >> > >>>> Do we need this key only for a case when an object
is being
> > inserted
> > >> > into a cache? If it’s so I would auto-generate a key using ‘long’
> as a
> > >> key
> > >> > type. I do remember that we provided the auto-generation for Spark
> > module
> > >> > in a some way that may be useful here.
> > >> > >>>>
> > >> > >>>> —
> > >> > >>>> Denis
> > >> > >>>>
> > >> > >>>>> On Sep 28, 2016, at 9:53 AM, Alexander Paschenko
<
> > >> > alexander.a.paschenko@gmail.com> wrote:
> > >> > >>>>>
> > >> > >>>>> Denis,
> > >> > >>>>>
> > >> > >>>>> That's not what I was asking about.
> > >> > >>>>> Currently DML implementation allows for dymanic
instantiation
> of
> > >> > keys,
> > >> > >>>>> in other words, user does not have to provide
value for
> > >> object-typed
> > >> > >>>>> _key column - instead, he may supply just field
values based
> on
> > >> which
> > >> > >>>>> _key will be dynamically instantiated/binary
built. And that's
> > the
> > >> > >>>>> whole point of this discussion as I see it: what
to do when
> > we've
> > >> > >>>>> binary built classless key that we build ourselves
inside SQL
> > >> engine
> > >> > >>>>> and don't know how to compute hash code for it?
> > >> > >>>>>
> > >> > >>>>> - Alex
> > >> > >>>>>
> > >> > >>>>> 2016-09-28 19:48 GMT+03:00 Denis Magda <dmagda@gridgain.com>:
> > >> > >>>>>> Alexander,
> > >> > >>>>>>
> > >> > >>>>>> As I guess if we have a key without a class
then it will be
> > >> > constructed using a BinaryBuilder instance and it’s user
> > responsibility
> > >> to
> > >> > set the has code at the end with BinaryBuilder.hasCode method. Sure,
> > all
> > >> > this cases must be well-documented in both Java Doc API and Apache
> > Ignite
> > >> > documentation.
> > >> > >>>>>>
> > >> > >>>>>> —
> > >> > >>>>>> Denis
> > >> > >>>>>>
> > >> > >>>>>>> On Sep 28, 2016, at 9:33 AM, Alexander
Paschenko <
> > >> > alexander.a.paschenko@gmail.com> wrote:
> > >> > >>>>>>>
> > >> > >>>>>>> Dmitry, Denis,
> > >> > >>>>>>>
> > >> > >>>>>>> OK, but I think it's necessary to address
also the cases
> when
> > >> > there's
> > >> > >>>>>>> no actual class for the key, and its
fields are simply
> > declared
> > >> in
> > >> > >>>>>>> XML. In this case, there are no fields
to be marked
> transient.
> > >> > What do
> > >> > >>>>>>> we do then? List transient fields in
XML separately?
> > >> > >>>>>>>
> > >> > >>>>>>> - Alex
> > >> > >>>>>>>
> > >> > >>>>>>> 2016-09-28 4:15 GMT+03:00 Dmitriy Setrakyan
<
> > >> dsetrakyan@apache.org
> > >> > >:
> > >> > >>>>>>>> Agree with Denis.
> > >> > >>>>>>>>
> > >> > >>>>>>>> - by default, all non-transient key
fields should
> > participate in
> > >> > the
> > >> > >>>>>>>> hashcode generation
> > >> > >>>>>>>> - when working on DDL, then the primary
key fields should
> > >> > participate in
> > >> > >>>>>>>> the hashcode
> > >> > >>>>>>>> - we should add a resolver to override
the default behavior
> > >> > (please
> > >> > >>>>>>>> propose the interface in Jira)
> > >> > >>>>>>>> - we should print out a warning,
only once per type, the
> the
> > >> > hashcode
> > >> > >>>>>>>> has been automatically generated
based on which fields and
> > which
> > >> > formula
> > >> > >>>>>>>>
> > >> > >>>>>>>> D.
> > >> > >>>>>>>>
> > >> > >>>>>>>> On Tue, Sep 27, 2016 at 5:42 PM,
Denis Magda <
> > >> dmagda@gridgain.com>
> > >> > wrote:
> > >> > >>>>>>>>
> > >> > >>>>>>>>> Hi Alexander,
> > >> > >>>>>>>>>
> > >> > >>>>>>>>> Vladimir’s proposal sounds
reasonable to me. However we
> must
> > >> > keep in mind
> > >> > >>>>>>>>> one important thing. Binary objects
were designed to
> address
> > >> the
> > >> > following
> > >> > >>>>>>>>> disadvantages a regular serializer,
like optimized
> > marshaller,
> > >> > has:
> > >> > >>>>>>>>> necessity to deserialize an object
on a server side every
> > time
> > >> > it’s needed.
> > >> > >>>>>>>>> necessity to hold an object in
both serialized and
> > deserialized
> > >> > forms on
> > >> > >>>>>>>>> the server node.
> > >> > >>>>>>>>> necessity to restart the whole
cluster each time an object
> > >> > version is
> > >> > >>>>>>>>> changed (new field is added or
an old one is removed).
> > >> > >>>>>>>>> If it will be needed to perform
step 3 for a default
> > >> > implementation of the
> > >> > >>>>>>>>> binary resolver just because
the resolver has to consider
> > new
> > >> > fields or
> > >> > >>>>>>>>> ignore old ones then such an
implementation sucks.
> Overall,
> > the
> > >> > default
> > >> > >>>>>>>>> implementation should use the
reflection coming over all
> the
> > >> > fields a key
> > >> > >>>>>>>>> has ignoring the ones that are
marked with “transient”
> > keyword.
> > >> > If a user
> > >> > >>>>>>>>> wants to control the default
resolver's logic then he can
> > label
> > >> > all the
> > >> > >>>>>>>>> fields that mustn’t be of a
final has code value with
> > >> > “transient”. This has
> > >> > >>>>>>>>> to be well-documented for sure.
> > >> > >>>>>>>>>
> > >> > >>>>>>>>> Makes sense?
> > >> > >>>>>>>>>
> > >> > >>>>>>>>> —
> > >> > >>>>>>>>> Denis
> > >> > >>>>>>>>>
> > >> > >>>>>>>>>> On Sep 26, 2016, at 12:40
PM, Alexander Paschenko <
> > >> > >>>>>>>>> alexander.a.paschenko@gmail.com>
wrote:
> > >> > >>>>>>>>>>
> > >> > >>>>>>>>>> Hello Igniters,
> > >> > >>>>>>>>>>
> > >> > >>>>>>>>>> As DML support is near, it's
critical that we agree on
> how
> > we
> > >> > generate
> > >> > >>>>>>>>>> hash codes for new keys in
presence of binary marshaller.
> > >> > Actually,
> > >> > >>>>>>>>>> this discussion isn't new
- please see its beginning
> here:
> > >> > >>>>>>>>>>
> > >> > >>>>>>>>>> http://apache-ignite-developers.2346864.n4.nabble.
> > >> > >>>>>>>>> com/All-BinaryObjects-created-
> > by-BinaryObjectBuilder-stored-
> > >> > >>>>>>>>> at-the-same-partition-by-default-td8042.html
> > >> > >>>>>>>>>>
> > >> > >>>>>>>>>> Still, I'm creating this
new thread to make getting to
> the
> > >> final
> > >> > >>>>>>>>>> solution as simple and fast
as possible.
> > >> > >>>>>>>>>>
> > >> > >>>>>>>>>> I remind everyone that the
approach that has got the
> least
> > >> > critics was
> > >> > >>>>>>>>>> the one proposed by Vladimir
Ozerov:
> > >> > >>>>>>>>>>
> > >> > >>>>>>>>>> <quote>
> > >> > >>>>>>>>>> I think we can do the following:
> > >> > >>>>>>>>>> 1) Add "has hash code" flag
as Denis suggested.
> > >> > >>>>>>>>>> 2) If object without a hash
code is put to cache, throw
> an
> > >> > exception.
> > >> > >>>>>>>>>> 3) Add *BinaryEqualsHashCodeResolver
*interface.
> > >> > >>>>>>>>>> 4) Add default implementation
which will auto-generate
> hash
> > >> > code. *Print
> > >> > >>>>>>>>> a
> > >> > >>>>>>>>>> warning when auto-generation
occurs*, so that user is
> aware
> > >> > that he is
> > >> > >>>>>>>>>> likely to have problems with
normal GETs/PUTs.
> > >> > >>>>>>>>>> 5) Add another implementation
which will use encoded
> > string to
> > >> > calculate
> > >> > >>>>>>>>> a
> > >> > >>>>>>>>>> hash code. E.g. *new BinaryEqualsHashCodeResolver("{a}
*
> > 31 +
> > >> > {b}")*.
> > >> > >>>>>>>>>> Originally proposed by Yakov
some time ago.
> > >> > >>>>>>>>>> </quote>
> > >> > >>>>>>>>>>
> > >> > >>>>>>>>>> After that, Sergi suggested
that instead of a "formula"
> we
> > >> keep
> > >> > just a
> > >> > >>>>>>>>>> list of the "fields" that
participate in hash code
> > evaluation,
> > >> > and
> > >> > >>>>>>>>>> with that list, we simply
calculate hash code just like
> IDE
> > >> > does -
> > >> > >>>>>>>>>> with all its bit shifts and
additions.
> > >> > >>>>>>>>>>
> > >> > >>>>>>>>>> I'm planning on settling
down with this combined
> Vlad-Sergi
> > >> > approach.
> > >> > >>>>>>>>>> Any objections?
> > >> > >>>>>>>>>>
> > >> > >>>>>>>>>> And an extra question I have:
Vlad, you suggest that we
> > both
> > >> > throw an
> > >> > >>>>>>>>>> exception on cache code absence
and that we might
> generate
> > it
> > >> > as the
> > >> > >>>>>>>>>> last resort. Do I understand
you correctly that you
> suggest
> > >> > generating
> > >> > >>>>>>>>>> random code only in context
of SQL, but throw exception
> for
> > >> keys
> > >> > >>>>>>>>>> without codes on ordinary
put?
> > >> > >>>>>>>>>>
> > >> > >>>>>>>>>> And yes, built-in hash codes
for JDK types are supported
> as
> > >> > well as
> > >> > >>>>>>>>>> items 1-2 from Vlad's list
(there's already fixed issue
> of
> > >> > IGNITE-3633
> > >> > >>>>>>>>>> for the flag and its presence
check).
> > >> > >>>>>>>>>>
> > >> > >>>>>>>>>> - Alex
> > >> > >>>>>>>>>
> > >> > >>>>>>>>>
> > >> > >>>>>>
> > >> > >>>>
> > >> > >>
> > >> >
> > >> >
> > >>
> >
>

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