Energy-Efficient Transaction Management for Mobile Adhoc Network Databases

Transcription

1 Eergy-Efficiet Trasactio Maagemet for Mobile Adhoc Network Databases 1st Author 1st author's affiliatio 1st lie of address 2d lie of address Telephoe umber, icl. coutry code 1st author's address 2d Author 2d author's affiliatio 1st lie of address 2d lie of address Telephoe umber, icl. coutry code 2d author s address ABSTRACT A Mobile Ad-hoc Network (MANET) is a collectio of mobile, wireless ad battery-powered odes without a fixed ifrastructure; so MANET fits well i disaster rescue ad military operatios. However, whe a ode rus out of power or has isufficiet power to fuctio, commuicatio may fail, discoectios may happe, executio of trasactios may be prologed, ad some trasactios may be aborted if they are time-critical ad miss their deadlies. I this paper, we propose a eergy-efficiet trasactio maagemet techique for MANET databases i a clustered etwork architecture where odes are divided ito clusters, each of which has a ode, called cluster head, resposible for the processig of all odes i the cluster. I our techique, i order to coserve eergy ad balace the eergy cosumptio amog servers so that the lifetime of the etwork is prologed, we elect cluster heads to work as coordiatig servers, re-elect a cluster head locally for a cluster whe its curret cluster head s remaiig eergy is low, ad propose a optimistic cocurrecy cotrol to offer high cocurrecy ad avoid wastig limited system resources. The simulatio results cofirm that our techique performs better tha other existig techiques i terms of trasactio abort rate ad degree of balacig eergy cosumptio amog servers. Keywords Mobile ad-hoc etwork, clusterig, trasactio maagemet, cocurrecy cotrol. 1. INTRODUCTION A mobile database system built o a Mobile Ad-hoc Network (MANET) is called a MANET database system. I this system, both cliets ad servers are mobile, wireless ad battery-powered, ad the databases are stored at servers ad accessed by cliets. As o fixed ifrastructure is required, MANET databases ca be deployed i a short time ad mobile users ca access ad maipulate data aytime ad aywhere, ad they become a attractive solutio to hadle missio-critical database Permissio to make digital or hard copies of all or part of this work for persoal or classroom use is grated without fee provided that copies are ot made or distributed for profit or commercial advatage ad that copies bear this otice ad the full citatio o the first page. To copy otherwise, or republish, to post o servers or to redistribute to lists, requires prior specific permissio ad/or a fee. Coferece 10, Moth 1 2, 2010, City, State, Coutry. Copyright 2010 ACM /00/0010 $ applicatios, such as disaster respose ad recovery system [4, 12, 1] ad military operatios like battlefields [1]. I these applicatios, trasactios must be executed ot oly correctly but also withi their deadlies. To fulfill this, a trasactio maagemet techique is essetial. Database maagemet systems esure coveiet ad efficiet access of databases for their users, ad trasactio Maager (TM) is a vital compoet i the system. TM is resposible for esurig that a database remais i a correct/cosistet state eve if system fails. Also TM esures that cocurret trasactio executios proceed without iterleavig [14]. However, because of the mobility ad portability, mobile odes have severe resource costraits i terms of capacity of battery, memory size ad CPU speed [8]. As the battery capacity is limited, it compromises the ability of each mobile ode to support services ad applicatios [6]. Also the battery techology is ot developed as rapidly as the mobile devices ad wireless techologies, so that the limited battery lifetime is always a bottleeck for the developmet of improved mobile devices [16]. Therefore, a suitable trasactio maagemet for MANET databases should be eergy-efficiet. Here, eergy efficiecy refers to the amout of service work that a system ca accomplish whe its battery capacity is limited [8]. Several trasactio maagemet techiques for MANET databases have bee proposed; however, either most of them do ot address the eergy efficiecy issue [3, 13], or other hadles the eergy efficiecy issue well but they assume that all trasactios are compesable (it is ot true for missio-critical applicatios) i their approach [10]. To fill i this gap, i this paper we propose a trasactio maagemet solutio that takes mobility, real-time costraits ad eergy efficiecy ito cosideratios, ad is specially desiged for missio-critical MANET databases. Our object is to miimize eergy cosumptio of each mobile ode ad balace eergy cosumptio amog mobile odes, so that mobile odes with low eergy do ot ru out of eergy quickly, ad thus, the umber of discoectios ad trasactio aborts due to low eergy or eergy exhaustio ca be reduced. The rest of the paper is orgaized as follows. Sectio 2 reviews some of the most recet mobile trasactio maagemet techiques. Sectio 3 describes the proposed MANET architecture. Sectio 4 presets our trasactio maagemet solutio. Sectio 5 presets the simulatio results. Fially Sectio 6 cocludes the paper with future research.

2 2. RELATED WORK I this sectio, first we briefly review proposed trasactio maagemet techiques for MANET databases, ad the we summarize them i terms of drawbacks. Sematic Serializability Applied to Mobility (SESAMO) [3] is proposed for MANET databases. SESAMO does ot require that a sigle mobile ode plays the role of the cetralized coordiator for all global trasactios. Moreover, SESAMO allows that subtrasactios commit idepedetly of the commitmet of their respective global trasactios. SESAMO is based o the sematic serializability, which assumes that databases are disjoit ad updates o a database oly deped o values of data of the same database; therefore, the atomicity ad global serializability ca be relaxed. However, i SESAMO, global trasactios still eed be serialized at each site usig strict 2PL globally, while at the same time, each site maitais the cosistecy of its ow local database. A trasactio maagemet for real-time MANET databases is proposed i [10]. To reduce eergy cosumptio, each mobile ode operates i three modes: active, doze, ad sleep; a cliet does ot blidly wait for a server to respod to a request, but a formula (sum of rutime estimate of the trasactio, commuicatio time ad delay time due to discoectio) is itroduced to compute the time that a cliet should wait for a server to respod. To reduce the chace that a ode may get discoected from the etwork due to power exhaustio, soft trasactios are set to the servers that have the highest remaiig eergy to process so that eergy cosumptio amog servers ca be balaced. The Partial Global Serializatio Graph (PGSG) techique proposed i [7] is adopted to guaratee trasactio atomicity ad isolatio ad PGSG assumes that all trasactios are compesable. I [13], the authors oly focus o the problem of settig up reasoable time-outs whe guarateeig atomicity for trasactio processig withi MANETs ad propose the Adjour State, which does ot rely o time-outs ad is a o-blockig state. That is, Adjour State allows cocurret trasactios to be processed while a distributed trasactio is waitig for the Coordiator s vote message to demad the commit decisio. Also, the Commit tree, a tree data structure that represets the executio status of all active sub-trasactios, is itroduced to efficietly coordiate trasactios. Although the solutio i [10] hadles the eergy problem well, PGSG requires that every trasactio is compesable ad compesable trasactios are ot always available i missiocritical applicatios. The approach i [13] maily focuses o trasactio atomicity ad does ot address the eergy problem. SESAMO does ot address the eergy problem either, ad it assumes that a MANET database is see as a collectio of sematic uits, which are disjoit ad do ot deped o each other; therefore the atomicity ad global serializability of global trasactios ca be relaxed [3]. However, the MANET databases for missio-critical applicatios caot relax the atomicity ad global serializability for their trasactios because each database depeds o each other such that sematic uits caot be defied. For example, i a disaster rescue sceario, before sedig firefighters to pursue some actios, the status of their equipmet has to be checked, where the firefighter database table may be stored o oe mobile server, ad the equipmet database table may be stored o aother mobile server. I a battlefield scee, before a tak fires cao, the locatios of the soldiers have to be checked to esure their safety, where the tak database table is stored o oe mobile server, ad the soldiers iformatio is located o aother mobile server. 3. PROPOSED ARCHITECTURE I this sectio, we itroduce our proposed architecture: a clustered MANET, which is built by applyig our robust weighted clusterig algorithm called PMW (Power, Mobility ad Workload) [18]. I the architecture as show i Figure 1, mobile odes are divided ito clusters, ad each cluster has oe cluster head workig as coordiatig server to be resposible for the trasactio processig withi the cluster. We choose this architecture because of two reasos. First, may MANET applicatios i the literature use grouped or clustered system architectures: disaster respose ad recovery system usig MANETs [4, 12], mobile telemedicie system [16], ad mobile group-based multimedia cooperatio system [9]. Secod, because every ode is mobile i MANETs, the etwork topology may chage rapidly ad upredictably over time. Accordig to [5], clustered architectures are proper to keep the etwork topology stable as log as possible, so that the performace of routig ad resource relocatio protocols is ot compromised. Figure 1. Architecture of a clustered MANET database 3.1 Classificatio of Mobile Nodes from Database Perspective ad Database Partitio I our clustered MANET architecture, depedig o the commuicatio stregth, computig power ad storage size, mobile odes are classified ito either cliets or servers. O cliets, oly the query processig modules that allow them to submit trasactios ad receive results are istalled; while o servers, the complete database maagemet system are istalled ad servers provide trasactio processig services. Servers are further classified ito coordiatig servers (actually replaced by cluster heads to solve eergy efficiecy issue) or participatig servers. Coordiatig servers are the oes which receive global trasactios, divide them ito sub-trasactios, forward these subtrasactios to appropriate participatig servers, ad maitai the ACID (Atomicity, Cosistecy, Isolatio, ad Durability)

3 properties of global trasactios. Participatig servers are the oes that process sub-trasactios trasmitted from coordiatig servers ad local trasactios submitted from local users, ad preserve their ACID properties. Coordiatig ad participatig servers are ot ecessarily physical uits, ad oe server ca fuctio as both. The etire database is partitioed ito local databases ad distributed at differet servers, ad there is o cachig or replicatio techique ivolved for simplicity. Trasactios are based o the simple flat model, which cotais a set of read, write, isert, ad delete operatios. However, whe operatios are checked for coflicts, isert ad delete operatios are treated just as write oes. Ay subset of operatios of a global trasactio that access the same server is submitted ad executed as a sigle sub-trasactio [7]. 3.2 Classificatio of Mobile Nodes from Network Perspective A clustered MANET cosists of cluster heads ad cluster members, where a cluster head (like a mobile support statio i a cellular mobile etwork) maages its clusters, coordiates itra/iter-cluster commuicatio ad so o. A cluster member is a ode that belogs to a cluster ad is ot a cluster head. 3.3 Electig Stable Cluster Head based o Nodes Power, Mobility ad Workload To capture the mobility of odes, we do ot cosider the absolute roamig speed. This is because it is easy to calculate the speed s quatity but it is hard to predict the directio of movemet. Without the directio, the speed s quatity aloe is ot appropriate to justify whether a ode is a good cadidate or ot. For istace, the speeds of two odes are small, but they both move i the opposite directios. As time goes, they will be out of each other s trasmissio rage ad get discoected from each other. Also the utilizatio of GPS is opted out because GPS cosumes the limited battery power of mobile odes. Istead, two mobility metrics, Relative Mobility (RM) [2] ad Mobility Predictio (MP), are itroduced to moitor the mobility of odes ad applied to determie whether a ode is suitable to be a cluster head as follows: For each ode j (1 j N for N odes i the etwork), after receivig two successive HELLO messages from every 1- hop eighbor i (1 i if there are eighbors), the RM ij is calculated by the Formula (3.1). rss ij1 ad rss ij2 are the received sigal stregth (RSS) that are read from the RSS idicator whe the first ad secod HELLO message from the same eighbor are received, respectively. Based o the value of RM ij, we ca say that if RM ij is equal to 1, the the ode j ad its eighbor i either do ot move at all or move with the same speed i the same directio; if RM ij is less tha 1, the they move close to each other; otherwise, they move away from each other. rss ij1 RM ij = rss ij 2 (3.1) For each ode j, to take ito accout the mobility of all 1- hop eighbors, MP j is calculated as the stadard deviatio of RM 1j, RM 2j,, RM j show i the Formula (3.2). However, for the stability of elected clusters, we prefer RM ij to be equal to or less tha 1 because we wat cluster heads ot to move away from their members. Thus, i the MP j calculatio the mea of RM ij (1 i ) is 1 istead of the actual mea. A ode j with a lower MP j meas that it stays closer to its eighbors, thus, it is a better cadidate for the cluster head amog its eighbors. MPj = 2 ( RM ij RM ij ) i= 1, where RM ij = 1 (3.2) Whe dealig with the limited battery power, we cosider ot oly the Remaiig Power (RP) of each ode but also its Power Decrease Rate (PDR) as the workload because odes with heavier workload cosume more eergy, so that we ca balace the power usage ad prevet cluster heads from ruig out of power quickly. I other words, for each ode j, the PDR j is cosidered because the RP j represets oly the curret state of power level ad the power will ru out soo if this ode usually has a heavy workload (for istace, it provides service as a server ad relays packets for may eighbors). The PDR j at time iterval [t 1, t 2 ] is calculated by usig the Formula (3.3), where rp j1 ad rp j2 are the remaiig power at time t 1 ad t 2, respectively. rp rp j1 j2 PDRj = t2 t1 (3.3) A ode with a lower PDR idicates that it was ot busy at least durig the iterval [t 1, t 2 ]. However, whe a ode had a busy work history, it most likely would be busy i the future as well. Sice the larger the time iterval is, the more accurate the PDR is i idicatig a ode s workload history, durig the iitial electio, each ode saves a copy of its iitial remaiig power ad iitial time as rp j1 ad t 1, such that a more accurate PDR ca be calculated i the future re-electio. Based o the above aalysis about power, mobility ad workload, it is obvious that a ode j is the best cadidate for a cluster head amog all its eighbors if its RP j is the highest, its MP j is the lowest ad its PDR j is the lowest. I other words, a ode with the highest weight is the best cadidate for a cluster head whe we combie these three metrics together as the weight, which is calculated i Formula (3.4). Sice these metrics have differet uits, we apply the iversed expoetial fuctio to ormalize MP j ad PDR j ad boud their values betwee 0 ad 1. RP j is left out because it is the remaiig power level i percetage ad its value is already betwee 0 ad 1. j MPj PDR j 1* e + f2 * RPj + f3 e W = f * (3.4) Due to less commuicatio stregth, less computig power ad smaller storage size, cliets caot be elected as cluster heads. The simulatio results from the NS-2 simulator did cofirm that PMW prologed the lifetime of a clustered MANET ad outperformed MOBIC [2] by as much as 23% o average. More details ca be foud i [18].

4 4. PROPOSED TRANSACTION MANAGEMENT I this sectio, we preset our trasactio maagemet techique that addresses the above eergy problem by aswerig the followig questios: how a trasactio is processed i a clustered MANET, how to hadle trasactio submissio from cliet to server, ad how to guaratee the atomicity ad isolatio properties of trasactios. 4.1 Overall Trasactio Flow i a Clustered MANET We assume that whe a cliet iitiates a trasactio T, T is set to its cluster head directly; the cluster head divides T ito several sub-trasactios, ad trasmits them to the appropriate participatig servers accordig to the global schema. Each participatig server processes the sub-trasactios locally, ad seds the results back to the cluster head. The cluster head rus the 2PC, gathers all results from the participatig servers ad validates T globally. The overall trasactio flow is also show i Figure 2. Figure 2. Trasactio flow i a clustered MANET 4.2 Hadlig Trasactio Submissio from Cliet to Server I MANETs, both the cliets ad servers are mobile, so fidig a route from oe ode to aother ode is ecessary before submittig a trasactio. Also i missio-critical MANET databases, sice mobile odes have eergy limitatio ad trasactios have timig costraits, a suitable trasactio maagemet techique has to balace the eergy cosumptio amog servers to reduce the chace that servers get discoected due to isufficiet power or power exhaustio; while at the same time the umber of aborted trasactios should be reduced due to missig their deadlies. Therefore, cliets submit trasactios directly to their ow cluster heads so that this elimiates the overhead that cliets must sped to idetify suitable servers to sed their trasactio to, ad the trasactios ca meet their deadlies. 4.3 Guarateeig Atomicity ad Isolatio of Trasactios To verify the isolatio property of trasactios we adopt the Sequetial Order with Dyamic Adjustmet (SODA) [17]. I the desig of SODA, the trasactio real-time costraits as well as mobility ad eergy limitatio of both servers ad cliets are take ito cosideratios. SODA is based o optimistic CC to offer high cocurrecy ad avoid ubouded blockig time that may cause may trasactios miss their deadlies, utilizes the sequetial order of committed trasactios to improve respose time, ad dyamically adjusts sequetial order of trasactios to reduce trasactio aborts. To deal with the atomicity, we simply adopt the well-kow 2-phase commit (2PC). I order to make SODA work effectively i clustered MANET databases, the coordiatig server fuctioality is combied i the cluster head because a cluster head is the earest server with the highest power i the eighborhood of cliets. Therefore, i our trasactio maagemet techique, cluster heads ad participatig servers cooperate together to esure the atomicity ad isolatio properties of trasactio. The fuctioalities of cluster heads ad participatig servers are show below. Note that oe server ca have both the fuctioalities at the same time The participatig server fuctioality A participatig server has followig tasks to accomplish: It receives ad processes sub-trasactios ad local trasactios. Whe it receives the request about the status of subtrasactios, it rus SODA locally based o the local sequetial order of committed trasactios. It seds the fial result to the requestig cluster head. If a sub-trasactio passes the validatio, the timestamp of read set is also set to the cluster head. If the sub-trasactio commits, it rebuilds the local latest sequetial order of committed trasactios by ruig the algorithm update_sequetial_order(), ad updates the read set, write set ad timestamps of both sets of committed trasactios. Oce a local or sub-trasactio commits, it tries to remove committed trasactios (or called outgoig odes i the local serializatio graph), which are ot serialized after ay active/committed trasactio, from the local sequetial order of committed trasactios The cluster head fuctioality A cluster head has followig tasks to accomplish: It receives global trasactios from cliets ad divides them ito sub-trasactios, which are set to appropriate participatig servers based o the global schema. It rus 2PC to request the status of sub-trasactios, ad at the same time requests timestamps of the read set. Oce it receives all successful messages of a global trasactio, it begis to validate this trasactio globally usig SODA i a critical sectio. After validatio, it seds the validatio result to each participatig server, ad seds the fial results to cliets. Whe a global trasactio commits, it updates its sequetial order by ruig the algorithm update_sequetial_order(), ad adds the read set, write set ad the timestamp of both sets.

5 Oce a global trasactio commits, it tries to remove committed trasactios (or outgoig odes i the global serializatio graph), which are ot serialized after ay active/committed trasactio, from the sequetial order of committed global trasactios. It periodically checks its remaiig power level. If the level is below a predefied threshold, it resigs its cluster head role ad elects a ew cluster head i the eighborhood, so that the power cosumptio amog servers is balaced. 5. PERFORMANCE EVALUATION The simulatio experimets are coducted to compare the performace of our proposed SODA with those of SESAMO [3] ad the most widely used CC protocol - S2PL (Strict 2-Phase Lockig). Here, we use the ames of CC techiques to represet the ames of trasactio maagemet techiques because CC is the most vital compoet i a trasactio maagemet techique. As we discussed earlier, SESAMO relaxes the atomicity ad global serializability due to its assumptio. The global serializability is guarateed by S2PL whe S2PL is combied with 2PC. Our simulatio model cosists of a trasactio geerator, a realtime scheduler that schedules trasactios usig early deadlie first, participatig servers, coordiatig servers or cluster heads for SODA oly, ad a deadlock maager for SESAMO ad S2PL. I the SODA model, a trasactio T issued by a cliet is distributed to its cluster head; the cluster head divides T ito several sub-trasactios, ad trasmits them to the appropriate participatig servers accordig to the global schema. Each participatig server processes the sub-trasactios locally, ad seds the results back to the cluster head. The cluster head rus the 2PC, gathers all results from the participatig servers ad validates T globally. The simulatio models for SESAMO ad S2PL are similar to that SODA except for a couple of poits. Oe is that SODA is applied locally ad globally to validate trasactios, while i SESAMO, strict 2PL is applied globally [3] ad locally [11], ad i S2PL, strict 2PL is oly ru oly locally. The other poit is that SESAMO ad S2PL use coordiatig servers istead of cluster heads. 5.1 Performace Metrics ad Simulatio Parameters Our simulatio is implemeted usig the AweSim simulatio laguage [Pritsker, 1999]. Global trasactios are defied as etities, ad mobile hosts are defied as resources with differet iitial eergy levels ad radomly distributed locatios. The simulatio parameters are show i Table 1. Due to space limitatio oly three performace metrics are preseted i this paper: abort rate defied i Formula (5.1), total eergy cosumed by all servers defied i Formula (5.2) ad average differece i eergy cosumptio betwee two servers defied i Formula (5.3). Sice i missio-critical applicatios, trasactios should be executed ot oly correctly but also withi their deadlies, that is, we use real-time trasactios to evaluate the performace. Therefore, i our simulatio, a trasactio will be aborted if either it misses its deadlie or the system could ot complete it successfully (e.g. whe it is aborted by the CC techique). Total umber of aborted trasactios *100% umber of geerated trasactios Abor t rate = Total (5.1) The secod performace metric is the total amout of eergy cosumed by all servers. This metric evaluates how the eergy efficiecy of each techique is, ad is computed with the followig formula, where is the total umber of servers, ad x i is the eergy cosumed by server S i. Total eer gy cosumed by servers = x i (5.2) i= 1 The third performace metric is the average differece i eergy cosumptio betwee two servers to evaluate how balaced the system is i terms of eergy cosumptio. The more balaced the system is, the loger lifetime the system has. The average differece i eergy cosumptio betwee two servers is computed i the followig formula, where is the total umber of servers, ad x i ad x j are total eergy cosumed by servers S i ad S j, respectively. Average differece i eergy cosumptio (5.3) Table 1. Simulatio Parameters = i = 1 j = 1 x - x ( 1) * Parameters Default Value Rage Simulatio Area 1000x Number of Cliets 40 - Number of Servers 20 - Arrival Rate (trasactios/secod) ~ 100 (Expoetially distributed) Discoectio Probability ~ 1.0 Read-oly Trasactio Probability ~ 1 Percetage off Discoectio Probability for Cluster 50% 10% ~ 100% Heads oly Total trasactios Simulatio Results Figure 3 shows the abort rates of SODA, SESAMO ad S2PL icrease whe the trasactio arrival rate icreases. The abort rate of SODA is much lower tha those of SESAMO ad S2PL maily because SODA is optimistic ad o-blockig, ad SESAMO s abort rate is slightly lower tha S2PL s. Although SESAMO does ot eforce global serializability, strict 2PL ruig both locally ad globally still blocks may coflictig trasactios. S2PL rus strict 2PL locally oly, but it eforces global serializability usig 2PC, so that all locks of subtrasactios are held util global trasactios commit, ad this situatio icreases the waitig time of coflictig trasactios i S2PL. Whe the arrival rate is gettig larger, abort rates of i j

6 SESAMO ad S2PL are almost the same. Also it is easy to see that the abort rates of SODA are gettig worse quickly whe the cotetio of trasactios icreases. the same reaso discussed above, ad they are almost the same whe the probability is 1. Sice SESAMO has at least 79% abort rate, this shows that SESAMO does ot cosider frequet discoectios. Figure 5 shows that the total eergy cosumptio of all servers icreases with the icrease of the arrival rate. This is trivial because each server has to work hard to process trasactios whe more trasactios are iitiated. Whe the arrival rate is greater tha or equal to 20, SODA cosumes at least 15 W less tha both S2PL ad SESAMO ad at the same time SODA has less abort rate as show i Figure 3. This cotributes to SODA is optimistic ad does ot hold limited system resource to prevet coflictig trasactios access them, ad also stable cluster heads work as coordiatig servers. Figure 3. Abort rate vs. arrival rate Figure 4 shows the abort rates of the three techiques icrease as the discoectio probability icreases. Discoectio probability 0.5 meas that 50% of commuicatios become discoected whe a mobile ode tries to commuicate with other odes. Oe of the major characteristics of MANET is frequet discoectios due to the mobility ad eergy limitatio of odes, ad ureliable wireless commuicatio betwee odes. Frequet discoectios of a mobile ode may result i log-lived trasactios ad may decrease the performace of MANET databases. Therefore, it is very importat to show the proposed SODA still works more efficietly eve though whe the discoectio probability is high. Figure 5. The total eergy cosumped by servers vs. arrival rate Figure 4. Abrot rate vs. probability of discoectio As show i Figure 4, the abort rate of SODA is at least 8% lower tha those of SESMO ad S2PL because SODA uses stable cluster heads as coordiatig servers, is optimistic so that it does ot block trasactios, ad utilizes the dyamic adjustmet of sequetial order of committed trasactios to reduce aborts. The abort rate of SESAMO is still slightly lower tha S2PL s due to Figure 6. The average differece i eergy cosumptio betwee two servers vs. arrival rate The average differece i eergy cosumptio betwee two servers by varyig the arrival rate is show i Figure 6. Through this metric, we wat to check if the eergy cosumptio is balaced amog servers. If a techique does ot balace eergy cosumptio amog servers, some server may ru out of power quickly ad cosequetly affects the whole database system. It is

7 easy to see that SODA balaces the eergy cosumptio best because cliets are grouped ito clusters ad always submit their trasactios to their ow cluster heads; however, i SESAMO ad S2PL, they submit trasactios radomly so that some servers are overloaded. 6. CONCLUSTIONS AND FUTURE WORK I this paper, we itroduced a trasactio maagemet techique that ca be used to support missio-critical applicatios such as disaster rescue ad battlefields. This techique cosiders trasactio real-time costraits as well as mobility ad eergy limitatio of both servers ad cliets. Our solutio is aimed at reducig the trasactio abort rate while savig the eergy cosumptio by servers ad balacig the eergy cosumptio amog servers, ad the simulatio results ideed cofirm that we reach our goal. For future research, we pla to icorporate data replicatio ito our model to improve the data access time ad availability. We will also ivestigate the effects of mobility (speed) of mobile odes ad umber of servers o these three performace metrics. 7. REFERENCES [1] Alampalayam, S. P., ad Sriivasa, S., " Itrusio Recovery Framework for Tactical Mobile Ad hoc Networks", the Iteratioal Joural of Computer Sciece ad Network Security, VOL.9 No.9, September [2] Basu, P., Kha, N., ad Little, T. D. C., A Mobility Based Metric for Clusterig i Mobile Ad Hoc Networks, I Proceedig of IEEE ICDC, April, 2001, pp [3] Brayer, A., ad Alecar, F. S., A Sematicserializability Based Fully-Distributed Cocurrecy Cotrol Mechaism for Mobile Multi-database Systems, Proceedig of the 16th Iteratioal Workshop o Database ad Expert Systems Applicatios (DEXA), 2005, pp [4] Catarci, T., de Leoi, M., Marrella, A., Mecella, M., Salvatore, B., Vetere, G., Dustdar, S., Juszczyk, L., Mazoor, A., ad Truog, H Pervasive Software Eviromets for Supportig Disaster Resposes, IEEE Iteret Computig, Vol. 12, No. 1, 2008, pp [5] Chatterjee, M., Das, S. K., ad Turgut,, D., WCA: A Weighted Clusterig Algorithm for Mobile Ad Hoc Networks, Cluster Computig, Vol. 5, 2002, pp [6] Chlamtac, I., Coti ad, M., Liu, J., Mobile Ad Hoc Networkig: Imperatives ad challeges, Ad Hoc Networks Publicatio, Vol. 1, Issue 1, July 2003, pp [7] Dirckze, R., ad Gruewald, L., A pre-serializatio trasactio maagemet techique for mobile multidatabases, Special Issue o Software Architecture for Mobile Applicatios, MONET 2000, pp [8] Fei, Y., Zhog, L., ad Jha, N. K., A eergy-aware framework for dyamic software maagemet i mobile computig systems, ACM Tras. o Embedded Computig Systems, April 2008 [9] Fudickar, S. J. F., ad Rebesburg, K., Mobile Group-based Multimedia Cooperatio System for MANETS, IEEE Multidiscipliary Egieerig Educatio Magazie, Jue 2007, Vol. 2, No. 2, pp [10] Gruewald, L., Baik, S. M., ad Lau, C., "Maagig real-time database trasactios i mobile ad-hoc etworks", Distributed ad Parallel Databases joural, Vol. 22, No. 1, August [11] Holada, M., Brayer, A., ad Fialho, S., Itroducig self-adaptability ito trasactio processig, SAC 2008, pp [12] Lu, W., Seah, W. K. G., Peh, E. W. C., ad Ge. Y., Commuicatios Support for Disaster Recovery Operatios usig Hybrid Mobile Ad-Hoc Networks, Proceedigs of the 32d IEEE Coferece o Local Computer Networks, Dubli, Irelad, 2007, pp [13] Obermeier, S., Böttcher, S., Hett, M., Chrysathis, P. K., ad Samaras. G., Blockig reductio for distributed trasactio processig withi MANETs. Distributed ad Parallel Databases 25(3): (2009). [14] Silberschatz, A., Korth, H. F., ad Sudarsha, S., Database Systems Cocepts, McGraw-Hill College. [15] Sklavos, N., Touliou, K., "Power Cosumptio i Wireless Networks: Techiques & Optimizatios", proceedigs of The IEEE Regio 8, EUROCON 2007, Iteratioal Coferece o "Computer as a Tool" (IEEE EUROCON'07), September 9-12, [16] Viswacheda, D. V., Arifiato, M. S., ad Barukag, L., Architectural Ifrastructural Issues of Mobile Ad hoc Network Commuicatios for Mobile Telemedicie System, I Proceedig of 4th Iteratioal Coferece o Scieces of Electroic, Techologies of Iformatio ad Telecommuicatios, Tuisia, [17] Xig, Z., Gruewald, L., ad Phag, K. K., "SODA: a Algorithm to Guaratee Correctess of Cocurret Trasactio Executio i Mobile P2P Databases", Proceedigs of the 19th Iteratioal Coferece o Database ad Expert Systems Applicatio Workshop, September 2008, pp [18] Xig, Z., Gruewald, L., ad Phag, K. K., A Robust Clusterig Algorithm for Mobile Ad-hoc Networks. To appear i the book Hadbook of Research o Next Geeratio Networks ad Ubiquitous Computig, IGI Global, 2010, i press.