Quorum Based Data Replication in Grid Environment

Transcription

1 Quorum Based Data Replicatio i Grid Eviromet Rohaya Latip, Hamidah Ibrahim, Mohamed Othma, Md Nasir Sulaima, ad Azizol Abdullah Faculty of Computer Sciece ad Iformatio Techology, Uiversiti Putra Malaysia {rohaya,hamidah,mothma,asir,azizol}@fsktm.upm.edu.my Abstract. Replicatio is a useful techique for distributed database systems ad ca be implemeted i a grid computatio eviromet to provide a high availability, fault tolerat, ad ehace the performace of the system. This paper discusses a ew protocol amed Diagoal Data Replicatio i 2D Mesh structure (DR2M) protocol where the performace addressed are data availability which is compared with the previous replicatio protocols, Read- Oe Write-All (ROWA), Votig (VT), Tree Quorum (TQ), Grid Cofiguratio (GC), ad Neighbor Replicatio o Grid (NRG). DR2M protocol is orgaized i a logical 2D mesh structure ad by usig quorums ad votig techiques to improve the performace ad availability of the replicatio protocol where it reduce the umber of copies of data replicatio for read or write operatios. The data file is copied at the selected ode of the diagoal site i a quorum. The selectio of a replica depeds o the diagoal locatio of the structured 2D mesh etwork where the middle ode is selected because it is the best locatio to get a copy of the data if every ode has the equal umber of request ad data accessig i the etwork. The algorithm i this paper also calculates the best umber of odes i each quorum ad how may quorums are eeded for N umber of odes i a etwork. DR2M protocol also esures that the data for read ad write operatios is cosistecy, by proofig the quorum must ot have a oempty itersectio quorum. To evaluate DR2M protocol, we developed a simulatio model i Java. Our results prove that DR2M protocol improves the performace of the data availability compare to the previous data replicatio protocol, ROWA, VT, TQ, GC ad NRG. Keywords: Data replicatio, Grid, Data maagemet, Availability, Replica cotrol protocol. 1 Itroductio A grid is a distributed etwork computig system, a virtual computer formed by a etworked set of heterogeeous machies that agree to share their local resources with each other. A grid is a very large scale, geeralized distributed etwork computig system that ca scale to iteret size eviromet with machies distributed across multiple orgaizatios ad admiistrative domais [1, 2]. Esurig efficiet access to such a huge etwork ad widely distributed data is a challege to G. Wag et al. (Eds.): RSKT 2008, LNAI 5009, pp , Spriger-Verlag Berli Heidelberg 2008

2 380 R. Latip et al. those who desig, maitai, ad maage the grid etwork. The availability of a data o a large etwork is a issue [3, 4, 5, 6] because geographically it is distributed ad has differet database maagemet to share across the grid etwork whereas replicatig data ca become expesive if the umber of operatios such as read or write operatios is high. I our work, we ivestigate the use of replicatio o a grid etwork to improve its ability to access data efficietly. Distributed computig maages thousads of computer systems ad this has limited its memory ad processig power. O the other had, grid computig has some extra characteristics. It is cocered to efficiet utilizatio of a pool of heterogeeous systems with optimal workload maagemet utilizig a eterprise's etire computatioal resources (servers, etworks, storage, ad iformatio) actig together to create oe or more large pools of computig resources. There is o limitatio of users or origiatios i grid computig. Eve though grid sometime ca be as miimum oe ode but for our protocol the best umber of odes should be more tha five odes to implemet the protocol. This protocol is suitable for large etwork such as grid eviromet. There are some research bee doe for replica cotrol protocol i distributed database ad grid such as Read-Oe Write-All (ROWA) [7], Votig (VT) [8], Tree Quorum (TQ) [9, 10], Grid Cofiguratio (GC) [11, 12], ad the latest research i year 2007 is Neighbor Replicatio o Grid (NRG) [13, 14, 15]. Each protocol has its ow way of optimizig the data availability. The usage of replica is to get a optimize data accessig i a large ad complex grid. Fig. 1 illustrates the usage of replica protocol i grid where it is located i the replica optimizatio compoet [16]. Resource Broker Iformatio Service User Iterface Replica Maager Cliet Replica Locatio Service Replica Optimizatio Storage Elemet Moitor Storage Elemet Network Moitor Fig. 1. Grid Compoets Iteract with Replica Maager i Grid I this paper, we preset a ew quorum-based protocol for data replicatio that provides both high data availability ad low respose time [17]. The proposed protocol imposes a logical two dimesioal mesh structure to produce the best umber of quorums ad obtai good performace of data availability. Quorums improved the performace of fault tolerat ad availability of replicatio protocols [18]. Quorums reduce the umber of copies ivolved i readig or writig

3 Quorum Based Data Replicatio i Grid Eviromet 381 data. To address the availability, we replicate data o the selected ode from the diagoal site of the 2D mesh structure, which has bee orgaized i quorums. This is because it is easy to access the database because of its middle locatio i the quorum. We use Java to ru this replicatio protocol. The paper is orgaized as follows. Sectio two itroduces Diagoal Replicatio i 2D Mesh (DR2M) protocol as a ew replica cotrol protocol. Sectio three, illustrates the DR2M algorithm. Sectio four discusses the results by comparig DR2M with the existig protocols ad the paper eds with a coclusio. 2 Diagoal Replicatio i 2D Mesh (DR2M) Protocol I our protocol, all odes are logically orgaized ito two dimesioal mesh structures. We assume that the replica copies are i the form of data files ad all odes are operatioal meaig that the copy at the odes is available. The data file is replicated to oly oe middle ode at the diagoal site of each quorum. This protocol uses quorum to arrage odes i cluster. Votig approach assiged every copy of replicated data object a certai umber of votes ad a trasactio has to collect a read quorum of r votes to read a data object, ad a write quorum of w votes to write the data object. I this approach the quorum must satisfy two costraits which are r + w must be larger tha the total umber of votes, v assiged to the copies of the data object ad w > v/2 [8]. Quorum is groupig the odes or databases as show i Fig. 2. This figure illustrates how the quorums for etwork size of 81 odes are grouped by odes of 5 x 5 i each quorum. Nodes which are formed i a quorum itersect with other quorums. This is to esure that these quorums ca read or write other data from other odes which are i aother quorum. The umber of odes grouped i a quorum, q must be odd so that oly oe middle ode from the diagoal site ca be selected such as site s(3,3) colored i black circles i Fig. 2. Site s(3,3) has the copy of the data file for read ad write operatio to be executed. Defiitio 2.1. Assume that a database system cosists of x odes that are logically orgaized i the form of two dimesioal grid structures. All sites are labeled s(i,j), 1 i, 1 j. The diagoal site of s(i,j) is s(,), where = 1, 2,,. From Fig. 2, for q1, the odes of the diagoal site, D(s) is {s(1,1), s(2,2), s(3,3), s(4,4), s(5,5)} i each quorum ad the middle ode s(3,3) has the copy of the data file. This figure shows that 81 odes have four quorums where each quorum actually itersects with each other. Node e i q1 is actually ode a i q2 ad ode e i q3 is actually ode a i q4 ad etc. Sice the data file is replicated oly o oe ode for each quorum, thus it miimizes the umber of database operatios. The selected ode i the diagoal sites is assiged with vote oe or vote zero. A vote assigmet o grid, B, is a fuctio such that, B(s(i,j)) {0, 1}, 1 i, 1 j where B(s(i,j)) is the vote assiged to site s(i,j). This assigmet is treated as a allocatio of replicated copies ad a vote assiged to the site results i a copy allocated at the diagoal site. That is,

4 382 R. Latip et al. 1 vote 1 copy. Let L B = B(s(i,j)), s(i,j) D(s) where L B is the total umber of votes assiged to the selected ode as a primary replica i each quorum. Thus L B = 1 i each quorum. q1 q2 s(1,1) s(1,1) a b c d e a b c d e s(2,2) s(2,2) f g h i j f g h i j s(3,3) s(3,3) k l m o k l m o s(4,4) s (4,4) p q r s t p q r s t s(1,1) u v w x a b c d s(5,5) y e u s(1,1) a v b w c x d s(5,5) y e s(2,2) s(2,2) f g h i j f g h i j s(3,3) s(3,3) k l m o k l m o s(4,4) s(4,4) p q r s t p q r s t s(5,5) s(5,5) u v w x y u v w x y q3 q4 Fig. 2. A grid orgaizatio with 81 odes, each of the ode has a data file a, b,, ad y, respectively Let r ad w deote the read quorum ad write quorum, respectively. To esure that read operatio always gets the updated data, r + w must be greater tha the total umber of votes assiged to all sites. To make sure the cosistecy is obtaied, the followig coditios must be fulfilled [8]. i. 1 r L B, 1 w L B ii. r + w = L B + 1. These two coditios esure that there is a oempty itersectio of copies betwee read ad write quorums. Thus, these coditios esure that a read operatio accesses the most recetly updated copy of the replicated data. Let S(B) = {s(i,j) B(s(i,j)) = 1, 1 i, 1 j } where i = j Defiitio 2.2. For a quorum q, a quorum group is ay subset of S(B) where the size is greater tha or equal to q. The collectio of quorum group is defied as the quorum set.

5 Quorum Based Data Replicatio i Grid Eviromet 383 Let Q(B m,q) be the quorum set with respect to assigmet B ad quorum q, the Q(B m,q) = {G G S(B) ad G q}. For example, from Fig. 2, let site s(3,3) be the primary database of the master data file m. Its diagoal sites are s(1,1), s(2,2), s(3,3), s(4,4), ad s(5,5). Cosider a assigmet B for the data file m, where B m (s(i,j)) is the vote assiged to site s(i,j) ad L B,m is the total umber of votes assiged to primary database i each quorum which is (s(3,3)) for data file m, such that B m (s(1,1)) = B m (s(2,2)) = B m (s(3,3)) = B m (s(4,4)) = B m (s(5,5)) = 1 ad L B,m = B m (s(3,3)). Therefore, S(B) = {s(3,3)}. For simplicity, a read quorum for the data file m, is equal to write quorum. The quorum sets for read ad write operatios are Q(B m,q1), Q(B m,q2), Q(B m,q3), ad Q(B m,q4), respectively, where Q(B m,q1) = {s(3,3)}, Q(B m,q2) = {s(3,3)}, Q(B m,q3) = {s(3,3)}, ad Q(B m,q4) = {s(3,3)}. Therefore, the umber of replicated data file m is four. 3 DR2M Algorithm DR2M is developed usig Java. The algorithm of the model is as i Fig. 3, where it shows the flow of the protocol. For the developmet of the simulatio some assumptios were made such as the etwork has o failure ad odes are accessible. To aalyze the performace of read ad write availability, below are the equatios where is the 2D mesh colum or row size, example is 7, thus 7 x 7 odes of grid is the etwork size ad p is the probability of data available which is betwee 0 to 1 whereas, q is the umber of quorum for a certai operatio such as read or write operatio. Eq. (1) is to calculate the data availability. i i Av, q = ( p (1 p) ) (1) i = q i Mai Iput umber of row or colum, N If N is odd iteger the Fid the umber of quorum, Q Q = 10 Fid umber of odes i each quorum, X X = Q Get the ext odd iteger after X Select the middle replica, R Copy the data file at R Else add oe virtual colum ad row, Col ew + Row New N = Col ew * Row New the Retur N to Mai. Fig. 3. Algorithm of DR2M protocol

6 384 R. Latip et al. A larger etwork has more quorums. The umber of colums ad rows i each quorum must be odd, to get the middle replica. DR2M protocol assumes all odes have the same data access level ad request umber. Fig. 3 is the algorithm for DR2M protocol. It illustrates how the algorithm is desiged ad implemeted. For Fig. 3, the umber of odes i the etwork must be odd ad if it is a eve umber the a virtual colum ad row is added meaig a empty ode of rows ad colum are located to make the selectio of the middle ode easier. To fid the best umber of quorum, Q, for the whole etwork size, x, Eq. (2) is used where is the umber of odes for row or colum. Q = 10 (2) For obtaiig the best umber of odes for each quorum, X, Eq. (3) is used where the umber of odes must be odd to make the selectio of the middle ode easy ad if X is ot odd the X will be the ext odd umber after /Q. X = (3) Q After the selected ode is chose, the data file is copied where it acts as a primary database for that particular quorum. Some protocol depeds o the frequet usage of the data to select that particular ode as the primary database. But for this protocol, a assumptio is made where every ode has the same level of data access ad umber of request. 4 Results ad Discussio I this sectio, DR2M protocol is compared with the results of read ad write availability of the existig protocols, amely: ROWA, VT, TQ, GC, ad NRG. Fig. 4 shows the results of read availability i 81 odes of etwork size. ROWA protocol has the higher read availability about average of 2.425% for probability of data accessig betwee 0.1 to 0.9 eve whe the umber of odes is icreased. This is because oly oe replica is accessed by a read operatio for all odes of etwork size but ROWA has the lowest write availability. Fig. 5 proves that the DR2M protocol has 4.163% higher of write availability for all probabilities of data accessig. This is due to the fact that replicas are selected from the middle locatio of all odes i each quorum ad by usig quorum approach helps to reduce the umber of copies i a large etwork. Fig. 5 illustrates the write availability for 81 umbers of odes, where the probability is from 0.1 to 0.9.

7 Quorum Based Data Replicatio i Grid Eviromet 385 Availability (Read) Vs Probability Availability (Read) ROWA VT TQ GC NRG DR2M Probability Fig. 4. Read availability results for existig protocols Availability (Write) Vs Probability 1.2 Availability (Write) ROWA VT TQ GC NRG DR2M Probability Fig. 5. Write availability results for existig protocols 6 Coclusios I this paper, DR2M protocol selects a primary database from the middle locatio of the diagoal site where the odes are orgaized i structure of 2D Mesh. By gettig the best umber of quorum ad usig the votig techiques have improved the availability for write operatio compared to all protocols ad has higher read availability compared to the latest techique, NRG. I the future, we will ivestigate the respose time to access a rage of data size i the grid eviromet ad this ivestigatio will be used to evaluate the performace of our DR2M protocol. Ackowledgemets. We would like to thak the Malaysia Miistry of Sciece, Techology ad Iovatio (MOSTI) for supportig our project uder the Fudametal Grat No: FR.

8 386 R. Latip et al. Refereces 1. Krauter, K., Buyya, R., Maheswara, M.: A Taxaomy ad Survey of Grid Resource Maagemet Systems for Distributed Computig. Iteratioal Joural of Software Practice ad Experiece 32(2), (2002) 2. Foster, I., Kesselma, C., Nick, J., Tuecke, S.: Grid Services for Distributed System Itegratio. Computer 35(6), (2002) 3. Ragaatha, K., Foster, I.: Idetifyig Dyamic Replicatio Strategies for a High Performace Data Grid. I: Iteratioal Workshop o Grid Computig, Dever (2001) 4. Lamehamedi, H., Szymaski, B., Shetu, Z., Deelma, E.: Data Replicatio Strategies i Grid Eviromet. I: ICAP 2003, pp IEEE Computer Sciece Press, Los Alamitos (2002) 5. Lamehamedi, H., Shetu, Z., Szymaski, B.: Simulatio of Dyamic Data Replicatio Strategies i Data Grids. I: The 17th Iteratioal Symposium o Parallel ad Distributed Processig, pp (2003) 6. Lamehamedi, H.: Decetralized Data Maagemet Framework for Data Grids. Ph.D. thesis, Resselaer Polytechic Istitute Troy, New York (2005) 7. Agrawal, D., El Abbadi, A.: Usig Recofiguratio for Efficiet Maagemet of Replicated Data. IEEE Trasactios o Kowledge ad Data Egieerig 8(5), (1996) 8. Mat Deris, M.: Efficiet Access of Replicatio Data i Distributed Database Systems. Thesis PhD, Uiversiti Putra Malaysia (2001) 9. Agrawal, D., El Abbadi, A.: The Geeralized Tree Quorum Protocol: A Efficiet Approach for Maagig Replicated Data. ACM Trasactios Database System 17(4), (1992) 10. Agrawal, D., El Abbadi, A.: The Tree Quorum Protocol: A Efficiet Approach for Maagig Replicated Data. I: 16th Iteratioal Coferece o Very Large databases, pp (1990) 11. Maekawa, M.: A Algorithm for Mutual Exclusio i Decetralized Systems. ACM Trasactios Computer System 3(2), (1992) 12. Cheug, S.Y., Ammar, M.H., Ahmad, M.: The Grid Protocol: A High Performace Schema for Maitaiig Replicated Data. IEEE Trasactios o Kowledge ad Data Egieerig 4(6), (1992) 13. Mat Deris, M., Evas, D.J., Sama, M.Y., Ahmad, N.: Biary Vote Assigmet o Grid For Efficiet Access of Replicated Data. It l Joural of Computer Mathematics, (2003) 14. Mat Deris, M., Abawajy, J.H., Suzuri, H.M.: A Efficiet Replicated Data Access Approach for Large Scale Distributed Systems. I: IEEE/ACM Cof. o Cluster Computig ad Grid, Chicago, USA (2004) 15. Ahamad, N., Mat Deris, M.: Maagig Neighbor Replicatio Trasactios i Distributed Systems. I: DCABES 2006, Chia (2006) 16. Kuszt, P., Laure, E., Stockiger, H., Stockiger, K.: Advaced Replica Maagemet with Reptor. I: CERN, Europea Orgaizatio for Nuclear Research, CH-1211 Geeva 23, Switzerlad (2000) 17. Mat Deris, M., Abawajy, J.H., Mamat, A.: A Efficiet Replicated Data Access Approach for Large-scale Distributed Systems. Future Geeratio Computer Systems 24, 1 9 (2007) 18. Jimeez-Peris, R., et al.: Are Quorums a Alterative for Data Replicatio? ACM Trasactios o Database Systems 28(3) (2003)