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Subject: RE: Fetch Group questions
Date: Thu, 7 Aug 2008 04:08:48 +0200
Message-ID: <12D996978341E849B21C51CC97F4771DEF5F4B@mail3.oams.com>
In-Reply-To: <1217463171165-661340.post@n2.nabble.com>
Thread-Topic: Fetch Group questions
thread-index: AcjyokCbVv//a+6GTvaomD+Lw3caRwFjBjKA
References: <12D996978341E849B21C51CC97F4771DE24E52@mail3.oams.com>
 <1217463171165-661340.post@n2.nabble.com>
From: "Michael Vorburger" <mvorburger@odyssey-group.com>
To: <users@openjpa.apache.org>

1.=20Thanks,=20that=20works=20great.

2.=20OK;=20understand=20perfectly=20what=20your=20saying;=20thanks=20for=20=
detailing.=20(Now
our=20data=20architect=20WILL=20probably=20cry=20that=20"there=20are=20unn=
cessary=20columns
fetched!".=20=20In=20the=20"upper=20layer"=20that=20is=20creating=20the=20=
FetchPlan,
dynamically,=20we=20would=20actually=20have=20the=20information=20to=20kno=
w=20that=20we=20will
NOT=20access=20A.c=20or=20A.c,=20so=20if=20a=20future=20OpenJPA=20version=20=
would=20offer=20a=20way
to=20override=20this,per=20attribute=20not=20globally,=20we=20could=20leve=
rage=20that;=20but
it's=20certainly=20not=20critical.=20=20Do=20you=20want=20a=20JIRA=20for=20=
this?)

3.=20Ignore;=20I=20think=20correctly=20configured=20Eager=20Fetching=20is=20=
what=20I'm
looking=20for;=20need=20to=20play=20more=20with=20this.=20I'll=20ask=20mor=
e=20specific
questions=20if=20needed.

4.=20Hm...=20I=20see.=20=20So=20to=20be=20safe,=20until=20this=20"bug"=20(=
?)=20gets=20addressed=20(can
it?=20will=20it?=20Would=20a=20JIRA=20help?),=20or=20actually=20rather=20f=
or=20the=20combination
of=20Cache/FetchGroup=20to=20work=20at=20all,=20would=20it=20be=20a=20good=
=20idea=20to=20may=20be
split=20all=20Entities=20into=20two=20types:=20A.=20fully=20cached=20ones=20=
(all=20instances
with=20"ALL"=20FetchGroup=20pinned=20in=20memory)=20-=20that=20should=20wo=
rk=20well=20for
"lookup=20table"=20kind=20of=20Entites.=20No=20FetchGroups=20used.=20=20B.=
=20No=20caching=20of
all=20other=20Entites=20(most=20Business=20Entites,=20all=20with=20lot's=20=
of=20columns),
and=20use=20of=20FetchGroups=20-=20good=20idea?=20=20Q:=20Is=20there=20a=20=
runtime=20API=20to=20the
@DataCache(enabled=3Dfalse),=20some=20configuration=20API=20to=20set=20whi=
ch=20classes
(globally,=20given=20a=20Class,=20not=20an=20instance)=20should=20be=20cac=
hed=20and=20which
not?

4=201/2=20[NEW]=20Q:=20On=20a=20Query=20where=20an=20association=20to=20a=20=
"fully=20cached"
Entity=20IS=20in=20the=20FetchGroup,=20can=20OpenJPA=20know=20this=20and=20=
NOT=20do=20the=20JOIN?
(Otherwise=20I'll=20think=20about=20building=20this=20into=20a=20layer=20o=
n=20top,=20although
it=20would=20be=20nicer=20if=20OpenJPA=20itself=20could=20handle=20this...=
)

5.=20[NEW]=20Q:=20Is=20there=20any=20significant=20runtime=20performance=20=
difference
between=20putting=20the=20@FetchGroup/s=20annotation=20on=20an=20@Entity=20=
and=20merely
"activating"=20it=20through=20FetchPlan.addFetchGroup(String=20groupName),=
=20as
opposed=20to=20"building"=20it=20and=20using=20lot's=20of=20invididual
FetchPlan.addField()=20?=20=20Probably=20not,=20but=20I=20thought=20I'd=20=
ask.

Thanks!


-----Original=20Message-----
From:=20Pinaki=20Poddar=20[mailto:ppoddar@apache.org]=20
Sent:=20jeudi,=2031.=20juillet=202008=2002:13
To:=20users@openjpa.apache.org
Subject:=20Re:=20Fetch=20Group=20questions


Hi,
>=201.=20Is=20the=20"default"=20fetch=20group=20ALWAYS=20active?=20
Almost=20ALWAYS.=20Unless=20you=20really,=20seriously=20do=20not=20want=20=
it,=20force
removal=20by
=20=20=20FetchPlan.removeFetchGroup(FetchGroup.NAME_DEFAULT);

after=20clearFetchGroup(),=20it=20will=20still=20load=20the=20fields=20of=20=
default=20fetch
group=20after=20resetFetchGroup(),=20it=20will=20load=20the=20default=20+=20=
any=20other
configured=20fetch=20groups.

>=202.=20Is=20there=20any=20way=20to=20configure=20OpenJPA=20to=20NOT=20ea=
gerly=20fetch=20direct=20
>=20relations

OpenJPA=20is=20not=20really=20'fetching'=20the=20direct=20relation=20unles=
s=20it=20is
included=20in=20the=20fetch=20group.=20If=20a=20row=20for=20A=20is=20read=20=
from=20database=20and
row(A)=20contains=20foreign=20keys=20to=20row(B)=20and=20row(C)=20(as=20th=
e=20case=20may=20be
for=20direct=20to-one=20mappings),=20then=20those=20FK=20values=20are=20re=
ad=20and=20stored=20in
a=20way=20that=20is=20invisible=20to=20user=20application.=20The=20referen=
ce=20A.b=20or=20A.c=20is
not=20populated.
The=20intermediate=20storage=20of=20foreign=20keys=20optimizes=20any=20sub=
sequent
traversal=20of=20A.b=20and=20A.c=20without=20a=20join.=20

Once=20A=20has=20lots=20of=20to-one=20relations,=20it=20is=20a=20valid=20c=
oncern=20that=20A=20will
store=20a=20lot=20of=20FK=20values=20in=20intermediate=20storage=20(perhap=
s=20without=20ever
using=20them),=20but=20just=20wanted=20to=20underline=20that=20there=20is=20=
no=20significant
performance=20penalty=20in=20such=20cases=20as=20the=20values=20are=20read=
=20from=20an
existing=20row.=20


>=203.=20When=20I=20do=20FetchPlan.addField()=20for=20a=20@ManyToMany=20or=
=20a=20
>=20@PersistentCollection(elementEmbedded=20=3D=20true)=20field,=20there=20=
is=20no=20eager

>=20fetching=20(like=20when=20the=20same=20field=20has=20FetchType.EAGER).=
..=20Should=20this
work?=20Can=20somebody=20point=20to=20any=20examples=20or=20test=20cases=20=
for=20this?=20Do=20we
need=20to=20fiddle=20with=20the=20EagerFetchMode=20join/parallel??

Not=20sure=20I=20understand=20the=20question=20--=20can=20you=20please=20e=
laborate?
=20
>=20a)=20in=20other=20words,=20query=20caching=20uses=20the=20Fetch=20Grou=
p=20as=20cache=20key)
No.=20

>=20b)=20only=20the=20"missing"=20columns=20are=20fetched=20and=20"merged"=
=20?
No.=20
If=20fetch=20plan=20is=20the=20only=20thing=20that=20is=20different=20betw=
een=20query=20Q1=20and
Q2=20and=20QueryCache=20is=20enabled,=20=20executing=20Q1=20followed=20by=20=
Q2=20will=20produce
an=20incorrect=20behavior.=20OpenJPA=20will=20consider=20Q2=20as=20the=20s=
ame=20as=20cached
version
Q1=20and=20will=20never=20apply=20fetch=20plan=20of=20Q2.=20


--
View=20this=20message=20in=20context:
http://n2.nabble.com/Fetch-Group-questions-tp534861p661340.html
Sent=20from=20the=20OpenJPA=20Users=20mailing=20list=20archive=20at=20Nabb=
le.com.


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