D y n a m i c L o a d B a l a n c i n g i n D i s t r i b u t e d V i r t u a l E n v i r o n m e n t s

boardpushyUrban and Civil

Dec 8, 2013 (3 years and 6 months ago)


Dynamic Load Balancing in Distributed Virtual En vironmen
Stephan Man tler and Dieter Sc hmalstieg
Vienna Univ yofT ec hnology A ustria
f step j dieter g gu wienct
This p ap er intr o duc es a new appr o ach for impr oving the sc alability of distribute d v onments
by using a c ombination of visibility cul ling for c ommunic ation and dynamic lo ad b alancing to ke ep
the system l o ad evenly distribute d F urther c ommunic ation optimizations as wel l as s ome p r eliminary
r esults ar epr esente d
tro duction message tering at run time T he en vironmen t is de
comp osed in to adjacen t parts whic h re a statically dis
In man y V irtual En vironmen ts there is a desire for
tributed o v er a net w ork f o s erv
h n um b ers of sim ultaneous p articipan ts within the
More sp ecially the system scalabilit yis no wnto
en vironmen t Ho w ev er these goals are defeated b y
longer limited b y n um ber of clien ts in the
limits of curren t soft w are and hardw are Increasing
load will degrade resp onsiv eness to the poin t vironmen t but the n ber of iclen ts that need to
the system is rendered useless T o o v ercome the re b e accoun ted or f b y one serv er T his s i without doubt
strictions distributed designs are needed that impro v e a drastic impro v emen t w er it is still p ossible for
the sc alability of the ystem s suc ha system to beecom o v erloaded as so on as
serv er reac hes its l imits ev en if the other computers
An optimal d esign will therefore minimize the com
are only v ery l igh tly loaded
m unication through a careful decomp osition of the
pap er tro duces an arc hitecture whic h
system additional computational ert can be used
aimed at aking t the scalabilit y of distributed virtual
to further reduce required comm unication ho w
vironmen ts one step further b y e ying dynamic
ev er care m b e t en that the increased pro essing c
lo ad b alancing k eep all serv ers v e
requiremen will not out w eigh impro v emen ts of
virtual w orld is decomp osed n i to regions he t distribu
tion nd hence the c ost of main tenance of whic his
An eien tnet w orking mec t p o
balanced among the a v ailable serv This arc hitec

is the se u of m ulticast comm unication I n addition
dirs from previous design b y allo wing a dy
to using a generic distributed approac h impro v
namic reconuration of the sim ulation sub d ivision
be obtained b y exploiting prop erties sp eci to
among serv ers including d atabase and net w ork con
the virtual vironmen t pplication a F or example if
nections Our approac h also allo ws to a nd v e
the ne vironmen t features ense d o cclusion suc hasin
serv ers at run time h is essen tial for In ternet
building in teriors the additional visibilit y i nformation
based applications
can b e used to reduce the n um b e r of essages m sen tto
h lien c t This reduction is t ypically p e rformed b ya
net w ork f o s erv ers eac h of whic h p ossesses geometry
A s ystem design with load balancing
nd th us visibilit y information ab out some part of
In order to k eep the system load distributed ev enly
the vironmen t w as the clien ts in part
o v connected hines sort of w orkload
As a c lien t an c see only a s mall fraction of the total
balancing to e place In the o v e of
n ber a v atars in suc h a system tering based
assigning a part of the en vironmen t to h serv er
up on visibilit y information greatly reduces the n um ber
an o v erloaded serv will to reduce its load b y
of messages that need to b e passed whic h leads to a
reducing the part of the w orld it has to handle while
signian t increase of the system scalabilit y
a serv noticing that has little or to do
F unkhouser describ ed an arc hitecture named R ING can request further w In this section w e outline

whic h uses static visibilit y information to p erform our system design whic hw as inspired b y the
nothing it er
aim er
of um
case ab tak needs
some mac all er
this ell as en
remo add
ts emen
se urp hat for hanism
the ts
The loaded enly to
ak ust
mplo en
is in This
ev ho
um en where
total the
envir irtual
tsS Mantler and D Schmalstie g Dynamic L o ad Balancing n i istribute D d Virtual Envir onments
number of regions on server A
number of regions on server B
Figure R e gions a r etr ansferr e db etwe en servers to
number of clients on server A
number of clients on server B
b alanc e system lo ad
Experiment Time
Figure L o b alancing in action Initial ly server A
arc hitecture ut b is capable to include load balancing
to o many clients and gr ly p asses r e gions and
among erv s ers
clients to server B As clients move ab out r an
F or simplicit y eha v e limited the en vironmen tto
domly they b e c ome evenly distribute d over the world

a D epresen r tation whic h is suien t for the rep

and c seBt au or eturn some r e to A
resen tation of building in teriors Visibilit y anc b e de
termined from the o or ap with a fast o nhey

algorithm hci h allo ws rapid p o in toell and cell aluation and Results
toell visibilit y computation The w orld consists of a
W eha v e mplemen i ted a p rotot yp e of the as de
n b er f o djacen a t nonn tersecting con v ex p olygons
scrib e d i n the previous sections and are c urren tly p r e
where ac e h edge of the p lygon o can b e either transpar
forming exp rimen e ts to examine the reaction of the
en t represen ting an op en do or or o paque for w alls
vironmen tto eth c hange of parameters orld size
The ize s of t hese p olygons determines the gran ularit y
n um ber of serv n ber of clien ts directed clien t
of the load balancing
v emen t s v random w alk T osim ulate a large n um
ber of h participan ts and to be able to repro
The s imple h euristic that has b een used in our im
duce the test situation under c hanging conditions the
plemen tation tries to estimate the serv er load b yex
v emen t of the clien ts is trolled b y rob ot pro
amining he t n um ber of encli ts as w ell as the regions
whic h are able to explore the w orld
By trying to k eep the clien t coun tbloe w a ertain c lev el
in teraction Preliminary results sho w that our ap
the etn w ork tra and required computing p o w er can
proac h s i f easible and app ar e encouraging
b e limited the tendency to w ards k eeping the n um ber
of regions do wn tries to k eep an o therwise unloaded
T o c onclude t he presen ted system c an b e regarded
serv er ad surprises lik e a large n um ber of
as a ramew f ork for further studies This future w ork
clien tering its regions
be aimed at examining poetn tial heuristics and
p erformance optimizations as w ellasthe in tegration
If it is decided t hat load balancing is required the
of the system with other ongoing r esearc h
heuristic tries to c ho ose a region for transfer that will
bring t he most b ene for the serv er i t he one t hat
Ac kno wledgmen ts This pro ject i s s p onsored b yteh
will mo v e as man y clien as p ossible to other
Austrian Science F oundation FWF under con
serv er
n um b er PMA T
Naturally cu h ransfers t should not cause another
serv er to b come e o v erloaded and necessitate addi
tional region transfers since this could cause un
w an ted oscillations as regions and clien ts are handed
M Macedonia M Zyda D Pratt D B rutzman
o v er bac k a nd forth Therefore here t are t w o limits on
and P Barham xploiting realit ywith m
the oad l s cale
groups A net w ork arc hitecture for largecale vir
tual en vironmen ts Pr o c
The high water mark dees the p oin tabo v e whic h
a ervs er tries to get rid of a r egion
T F unkhouser Net w ork top ologies for scalable
If a s erv er load falls b elo w low ater w mark it
m ultiser virtual en vironmen ts Pr o c e e dings of
will try to tak eo v er a region from another serv er
VRAIS Santa Clar aCA pp
The latter is needed to ev enly distribute the load
D Sc hmalstieg and R T obler xploiting coher
ev en in areas where the o v erall load is lo wb y r equiring
ence in d visibilit y c omputation
ored serv ers to tak e o v er some of the w ork
and Gr aphics pp
other erv s ers

the ts
en ts
without grams
con mo

um ers

adual has