A CLUSTERING-BASED HYBRID REPLICA CONTROL PROTOCOL FOR HIGH AVAILABILITY IN GRID ENVIRONMENT

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1 Journal of Computer Science 10 (12): , 2014 ISSN: R. Latip et al., Thi open acce article i ditributed under a Creative Common Attribution (CC-BY) 3.0 licene doi: /jcp Publihed Online 10 (12) 2014 ( A CLUSTERING-BASED HYBRID REPLICA CONTROL PROTOCOL FOR HIGH AVAILABILITY IN GRID ENVIRONMENT 1 Rohaya Latip, 1 Zulaile Mabni, 2 Hamidah Ibrahim, 1 Azizol Abdullah, 1 Manida Huin 1 Department of Communication Technology and Network, Faculty of Computer Science and Information Technology, Univerity Putra Malayia, Serdang, Selangor, Malayia 2 Department of Computer Science, Faculty of Computer Science and Information Technology, Univerity Putra Malayia, Serdang, Selangor, Malayia Received ; Revied ; Accepted ABSTRACT In recent year, with the emergence of grid computing ytem, the number of ditributed ite ha become very large. When thouand of ite involved in a grid computing ytem, data replication can improve data availability, communication cot and provide fault-tolerance in the ytem. In the literature, many replica control protocol have been propoed for managing replicated data. However, in large cale ditributed ytem, mot of thee protocol till require a bigger number of replica for maintaining conitency, thu degrade the performance of the protocol. Therefore, in thi tudy, we propoed a new replica control protocol named Clutering-Baed Hybrid (CBH) protocol. CBH protocol employ a hybrid replication trategy by combining the advantage of two common replica control protocol into one to improve the performance of the exiting protocol. We analyzed the communication cot and availability of the operation and compare CBH protocol with recently propoed replica control protocol named Dynamic Hybrid (DH) protocol. A imulation model wa developed uing Java to evaluate CBH protocol. Our reult how that the propoed protocol provide lower communication cot and higher data availability than DH protocol. Keyword: Replica Control Protocol, Data Replication, Data Availability, Communication Cot 1. INTRODUCTION A grid i a very large cale ditributed network computing ytem that i deigned to provide reliable acce to data and computational reource over a wide area network and acro organizational domain (Foter et al., 2001; Krauter et al., 2002). In a largecale ditributed ytem and dynamic network uch a grid, data replication ha been implemented to provide high availability, fault tolerance and increae the performance of the ytem (Lamehamedi et al., 2002; a technique of creating multiple copie of data item at ditributed ite. However, ome iue arie in dealing with replication of data. A major iue with replication i maintaining conitency of the replica (Belalem and Slimani, 2006; Yang et al., 2007; Radi et al., 2008). When data are replicated at everal ite, a conitency control protocol mut be enforced to enure the conitent view of the data. Other iue i communication cot where, in general, a the ytem ize grow, the cot of executing operation in replicated databae increae ince many replica may need to be Latip et al., 2008; Mabni and Latip, 2011). Replication i acceed for maintaining the conitency of the replica Correponding Author: Rohaya Latip, Department of Communication Technology and Network, Faculty of Computer Science and Information Technology, Univerity Putra Malayia, Serdang, Selangor, Malayia 2442

2 (Choi and Youn, 2012). The availability of a data on a large network i another iue (Lamehamedi et al., 2002; Lamehamedi et al., 2003; Latip et al., 2009) becaue geographically it i ditributed and ha different databae management to hare acro the grid network. In a ditributed ytem, copie or replica of an object may be tored at everal ite in the network. Thee multiple copie of an object mut appear a a ingle logical object to the tranaction which i known a one-copy equivalence (Berntein and Goodman, 1984). Two operation which are read and are allowed on replicated data. A Read Quorum (RQ) or Write Quorum (WQ) i defined a a et of copie that i ufficient to execute the read or operation. The election of a quorum mut atify the quorum interection property to enure one-copy equivalence among the replica and maintain their conitent tate. The property tated that for any two operation o[x] and o [x] on an object x, where at leat one of them i a, the quorum mut have a nonempty interection (Gifford, 1979). Thu, the baic property employed in maintaining conitency of replicated data i to require conflicting operation to lock at leat one common copy and thi i enforced by the replica control protocol. In recent year, with the emergence of grid computing ytem, the number of ditributed node ha become very large. However, in large cale ytem, mot of the earlier replica control protocol till require a bigger number of replica for read and operation, thu degrade the performance of the protocol. The degradation of performance i due to the conitency enforcement where a large number of replica mut be acceed through the wide area network. In thi tudy, we propoe a new replica control protocol called Clutering-Baed Hybrid (CBH) protocol for grid environment. The propoed protocol employ a hybrid replication trategy by combining the advantage of two common replica control protocol into one to improve the performance of earlier protocol. The propoed protocol group node into cluter and organize thee cluter into a tree tructure which enable the protocol to minimize the number of replica for read or operation a well a reduce the communication cot and provide high availability. 2. RELATED WORKS Thi ection decribe the related work in replica control protocol. They differ from each other mainly in the number of replica involved in performing the read and operation. Thee protocol have atified the quorum interection property to enure one-copy equivalence among the replica and maintain their conitent tate Primary Copy Protocol Primary Copy (PC) protocol i a imple algorithm that deignate one copy of a data object a primary copy (Stonebraker, 1979; Ahamad et al., 1992; Zhou and Holme, 1999). The node that maintain the primary copy of the data object i therefore reponible for maintaining conitency of the object. Any other node that maintain a non-primary copy i known a a lave copy. A read and operation are executed only at the primary copy. For the operation, once the primary copy i updated, it will be propagated out to all the node that maintain the lave copie. The communication cot for read and operation are low becaue only one replica i acceed by the operation. The advantage of thi protocol i that it i eay to implement a compared to other protocol and it i one of the mot widely implemented replication technique. However, it ha a limitation where, if the node that maintain a primary copy fail, then an update operation can no longer be performed until the node become available again Ree Quorum Protocol Agrawal and Abbadi (1990) propoed the Tree Quorum (TQ) protocol, which i baed on a logical tree tructure over a network (Agrawal and Abbadi, 1990). Figure 1 illutrate the diagram of a tree quorum tructure with thirteen copie in a tree of height = 2 and degree of node D = 3, where every copy repreent a replica. In thi protocol, a read quorum conit of the root replica. If the root i inacceible, then majority replica of it children are added a member of thi quorum. Furthermore, for every inacceible replica, majority replica of it children are added a member and o forth. The example of valid read quorum of Fig. 1 are 1} and {2,3} when root replica i inacceible and {5,6,8,9} when replica-2 and replica-3 are inacceible. On the other hand, a quorum i contructed by having a it member the root and any majority replica of the root children and any majority replica of their children and o forth until the leave are reached. Figure 1, the example of valid quorum are {1,2,3,5,6,8,9} and {1,3,4,9,10,11,12}. The trength of thi protocol i that read operation may acce only one replica. Thu, thi protocol allow very low read cot in the bet cae. However, it ha ome drawback uch a, a the level of the tree increae, the number of replica grow rapidly, thu increae the communication cot. 2443

3 3. THE PROPOSED PROTOCOL Fig. 1. A tree organization of 13 copie of data object (Agrawal and Abbadi, 1990) 2.3. Dynamic Hybrid Protocol A recently propoed hybrid replica control protocol i Dynamic Hybrid (DH) protocol (Choi and Youn, 2012). Thi protocol combine the grid and tree tructure o that the overall topology can be flexibly adjuted uing the tree height, number of decendant and grid depth. Figure 2 illutrate the network of Dynamic Hybrid protocol with 31 replica in (3,3,2) topology, where the three argument are repreenting the height h, number of decendant and grid depth g repectively. In the tree tructure of height h, the read operation read the root replica or the decendant of the root replica if the root i not available. The decendant of the root erve a the new root replica of the ub tree. The proce i repeated until level h-1 i reached. Furthermore, in the grid network of depth g, read operation read replica or go to the next level if one of the replica i not available. Thu, the read cot i only 1, if the root replica i available. The example of valid read quorum of Fig. 2 are {R0} and {R1, R2, R3} and {R2, R3, R4, R5, R6}. Meanwhile, the operation read the root replica, one replica of the root decendant, one replica of thee previouly elected replica decendant and o forth until the leave are reached. Furthermore, in the grid network of depth g, operation read only one replica in each level down to the lat level. Figure 2, the example of valid quorum are {R0, R1, R4, R13, R22} and {R0, R2, R7, R16, R27}. The trength of thi protocol i that it capitalize the merit of tree and grid protocol to allow low operation cot and high availability. However, thi protocol ha drawback where, a the network ize grow, large number of replica till need to be acceed to maintain data conitency and therefore, degrade the performance of the ytem. In thi ection, we preent the ytem model and algorithm for the propoed protocol called Clutering-Baed Hybrid (CBH) Protocol. In thi tudy, the term a number of node and a number of ite will be ued interchangeably Sytem Model The ytem conit of N ite that communicate with each other by ending meage over a communication network. We aumed that ite fail independently and communication link do not fail to deliver meage. In CBH protocol, the N ite in the network are logically grouped into everal noninterecting group. For the purpoe of illutration we hall divide the N ite into N dijoint group with each group having approximately N ite. Each group i called a cluter. Thee cluter are logically organized a a tree of height h and decendant. We defined the node in the tree to be a equence of cluter C 0, C 1, C i, C i+1, C n. We aume that the node in each cluter are logically organized into two dimenional grid tructure. For example, if CBH protocol conit of 81 node, it will be divided into 9 cluter with 9 node in each cluter. The node in each cluter will be logically organized in the form of 3 3 grid. Figure 3, an example of a ternary tree of height = 2 with 81 node i preented. Each cluter deignate the middle node of the cluter a the cluter head which i colored in black in Fig. 3 and ha the replica or primary copy of the data object. The center of the cluter i elected becaue it i the hortet path to get a copy of the data from mot of the direction in the cluter Propoed Algorithm Here, we decribe the hybrid trategy of CBH protocol, where it combine the advantage of two common replica control protocol namely Tree Quorum (TQ) protocol and Primary Copy (PC) protocol. Figure 3, we how a ytem with 81 node for which we ue TQ protocol on top of PC protocol a the replication trategy. In order to implify the decription, we aumed that every replica i aigned exactly one vote. Figure 3 how a ytem with 81 node where the nine cluter named C 0, C 1,,C 8 are logical replica which are managed by uing TQ protocol. The logical replica C 0 erve a the root cluter, wherea the logical replica C 1,,C 8 are it decendant. Each logical replica contain a cluter of phyical node with one middle node called phyical replica which ha the replica or primary copy of the data object. 2444

4 Fig. 2. A network for Dynamic Hybrid protocol of 31 replica in (3, 3, 2) topology (Choi and Youn, 2012) Fig. 3. Sytem Model of CBH in a ternary tree of height = 2 with 81 node The phyical replica in the root cluter C 0 i called root replica. Thu, for a ytem with N node, there will be N cluter and N replica. To illutrate the algorithm, the replication trategy involve two trategie: Local Replication, where PC protocol i ued for the replication trategy for managing the phyical replica within a cluter and Global Replication, where TQ protocol i ued a the replication trategy for managing the logical replica between cluter Read Operation A read operation according to TQ protocol, which i ued a the global replication, can be performed by reading the root replicac 0 if C 0 i acceible or if the root replica i inacceible then majority replica of it children are added a member of thi quorum. Furthermore, for every inacceible replica, majority replica of it children are added a member and o forth. In CBH protocol, a logical replica i available for a read operation if a read operation can be performed on the phyical replica which it contain, uing the applied local replication trategy which i PC protocol. Thi mean that the precondition for reading a logical replica i a read quorum of RQ = 1 if it contained phyical replica i acceible for read operation. Thu, in Fig. 3, auming that the root replica i acceible, by employing TQ Protocol, thi lead to a minimal read cot of 1. However, if the root replica i not available, then the majority replica of it children have to be acceed which reult in the read cot of 2. The example of valid read quorum of Fig. 3 are {C 0 } and {C 1, C 2 } if the root replica i not available Write Operation A operation according to TQ protocol, which i ued a the global replication, can be performed by reading the root replicac 0 and any majority replica of the root children and any majority replica of their children and o forth until the leave are reached. In CBH protocol, a logical replica i available for a operation if a operation can be performed on the phyical replica which it contain, uing the applied local replication trategy which i PC protocol. Thi mean that the precondition for writing a logical replica i a quorum of WQ = 1 if it contained phyical replica i acceible for operation. Thu, in Fig. 3, auming that the root replica i acceible, a operation performed on a logical replica require WQ = 1 of it phyical replica. Thu, by employing TQ protocol, we obtain a cot of 7. An example of valid quorum of Fig. 3 i {C 0, C 1, C 2, C 4, C 5, C 7, C 8 } Correctne of CBH Algorithm Here, we demontrate that the read and quorum contructed by the CBH protocol will alway have a non-empty interection. Theorem The CBH protocol guarantee the interection of read and quorum. Proof = The proof i by induction on the height of the tree. 2445

5 Bai = The theorem hold for a tree of height zero, ince there i only one phyical replica in the tree. Induction Hypothee = Aume that the theorem hold for a tree of height h. Induction Step = Conider a tree of height h + 1. The Read Quorum (RQ) and Write Quorum (WQ) contructed for thi tree will be of the following form: RQ = {Root Replica} or {Majority of phyical replica of ub tree of height h} WQ = {Root Replica} and {Majority of phyical replica of ub tree of height h} If a read quorum conit of the root replica of the tree, it i guaranteed to have a nonempty interection with any quorum ince a root replica mut be acceed in any quorum. On the other hand, if the read quorum conit of a majority of phyical replica for ub tree of height h, it i guaranteed to have at leat one ub tree in common with any quorum. Since the ub tree are of height h, the induction hypothei guarantee that read and quorum will have a non-empty interection. Hence, by induction, the CBH protocol guarantee non-empty interection between read and quorum. Therefore, for the propoed CBH, the read/ conflict can be guaranteed to be detected becaue a read operation lock the root replica while a operation lock the root replica and majority of phyical replica of the decendant. A for the conflict between two operation, it can be guaranteed to be detected ince any two operation have to hare the root replica. For example, in Fig. 3, valid RQ are {C 0 } and {C 1, C 2 }, wherea, valid WQ i {C 0, C 1, C 2, C 4, C 5, C 7, C 8 }. Note that C 1 i included in both the valid RQ and WQ for detecting read/ conflict. 4. PERFORMANCE ANALYSIS AND COMPARISON A imulation model wa developed uing Java to validate CBH protocol. In thi ection, we evaluate and compare the performance which are read and communication cot and data availability of CBH and DH protocol Cot Analyi The communication cot of an operation i computed baed on the number of replica involved in the read or operation. The read operation of DH protocol need to acce only the root replica which i very effective if the root replica i available. The minimum read cot C read i Equation 1: min( C read ) = 1 (1) And the cot C that depend on the value of h and g i Equation 2: C = h g (2) On the other hand, for CBH protocol, the communication cot i etimated baed on the TQ protocol a given in (Chung, 1994), where h denote the height of the tree, D i the degree of logical replica in the tree and M i the majority of D where Equation 3: M D + 1 = 2 (3) Therefore, for a tree of height h, the maximum quorum ize i M h and the communication cot for read operation C CBH, R i in the range of 1 C CBH, R M h. Meanwhile, the communication cot for operation C CBH, W i given in Equation 4: i CCBH, W = M (4) where, i = 0,,h. For the read communication cot, both CBH and DH protocol have the ame minimum read cot of 1, which i achieved by acceing only the root replica of the tree if the root replica i acceible. Table 1 and Fig. 4 illutrate the communication cot of CBH and DH protocol for an example ytem with different total number of node, n = 81, 121, 225 and 289. Here, the protocol have the ame number of decendant which i 3 but they differ in their height baed on the number of node. A an example, for 121 node in the ytem, DH protocol i baed on height of 4 and grid depth of 3 which i configured in (4,3,3) topology and CBH i baed on height of 2. For the operation a illutrated in Table 1 and Fig. 4, it i apparent that the overall communication cot for CBH protocol i lower than that of DH protocol. It can be een that CBH need to acce only 9 replica on 225 copie for the operation. On the other hand, for DH with 225 copie, the number of replica that need to be acceed for performing operation i 11. The reult in Fig. 4 how that the average cot for CBH i 8.0 and DH i 9.5. Thu, CBH ha reduced the average cot by up to 15.8% compared to DH. 2446

6 Thu, the overall availability of operation for DH i a given in Equation 8: = k With ( l) k p ( ) 1 k 1 ( l 1) k ( l 1) ( ) k = Where l = h 2 (0) k k G( l) p p ( 1 p). k 1 (8) Fig. 4. Comparion for the cot of the protocol with 81, 121, 225 and 289 node Table 1. Comparion for the cot of the protocol Number of node Protocol N = 81 N = 121 N = 225 N = 289 DH CBH On the other hand, for CBH protocol, the overall availability i obtained uing the combination of availability for PC protocol and TQ protocol. The availability of read operation of PC protocol i a given in Equation 9, where p i the probability of data file acceing between 0.1 to 0.9 and i i the increment of n. n = 1 n APC, R = p p = p i 1 i i n i n ( 1 ) 1 ( 1 ) (9) Thu, the CBH overall availability of read operation for a tree of height h + 1 i a given in Equation 10: 4.2. Availability Analyi In thi ection, we analyzed the read and availability of the protocol. In DH protocol, the overall availability i obtained uing the availability of tree and grid tructure. The availability of read operation of the grid tructure i a given in Equation 5: D D ACBH, R = A, ( 1, ) h 1 PC R + A + PC R i= M i A ( 1 ACBH R ) i CBH, R h, h With A = A CBH, R 0 PC, R D i (10) ( ) G( g 1) ( ) G g = p + 1 p. (5) read read Thu, the overall availability of read operation for DH protocol i a given in Equation 6: ( ) ( l) ( l 1) read p 1 p.( read ) = + with = wherel = h 1 (0) G( g) read read (6) The availability of operation of the grid tructure i a given in Equation 7: = k where, l = g 1 G( l ) k k G( l 1) p ap ( 1 p). k = 1 k p G(0) k = k = 1 ( 1 p ) k (7) The availability of operation of PC protocol i a given in Equation 11: n = 1 n APC, W = p p = p n i i ( 1 ) n i n 1 ( 1 ) (11) Thu, the CBH overall availability of operation for a tree of height h + 1 i a given in Equation 12: D A APC w A A With ( ) D i D i CBH, W =, 1 CBH, W 1 h+ h CBH, W h i= M i A = A CBH, W 0 PC, W (12) Figure 5 and 6 how the read and availability of CBH and DH protocol for 121 node repectively. We aume that all data copie have the ame availabilitie. 2447

7 logically grouped into everal noninterecting group called cluter and organized in a tree tructure. CBH protocol employ a hybrid replication trategy by combining the advantage of Primary Copy (PC) protocol and Tree Quorum (TQ) protocol to improve the performance of the exiting protocol. In CBH, by grouping the node into cluter and having only one replica in each cluter ha reulted in a mall number of replica involved in performing read and operation. The analyi of CBH protocol wa preented in term of communication cot and data availability. Compared to DH protocol, CBH require lower communication cot while providing higher read availability which i preferred for large cale ditributed ytem. Fig. 5. Comparion of read availability for 121 node 6. ACKNOWLEDGEMENT We wih to acknowledge the upport of Malayian Minitry of Science, Technology and Innovation (MOSTI) under the Fundamental Grant No: FR Author Contribution All author equally contributed in thi work Ethic Thi article i original and contain unpublihed material. The correponding author confirm that all of the other author have read and approved the manucript and no ethical iue involved. Fig. 6. Comparion of availability for 121 node Figure 5, we can ee that the read availability for CBH protocol i higher than DH protocol. Thi i due to CBH need only to acce mall number of replica for the read operation. The reult how that CBH protocol ha average of 16.8% higher for read availability compared to DH protocol for all probabilitie of data acceing. However, in cae of availability for 121 node, DH protocol i better than CBH protocol a illutrated in Fig CONCLUSION In thi tudy, a new replica control protocol named Clutering-Baed Hybrid (CBH) protocol ha been propoed for the management of replicated data in large cale ditributed ytem epecially in grid environment. In the propoed protocol, the N ite in the network are 7. REFERENCES Agrawal, D. and A. El Abbadi, The tree quorum protocol: An efficient approach for managing replicated data. Proceeding of the 16th International Conference on Very Large Databae, Aug , Bribane, Autralia, pp: DOI: / Ahamad, M., M.H. Ammar and S.Y. Cheung, Replicated data management in ditributed ytem. Read. Dit. Comput. Syt., DOI: Belalem, G. and Y. Slimani, A hybrid approach for conitency management in large cale ytem. Proceeding of the International Conference on Networking and Service, Jul , IEEE Xplore Pre, Slicon Valley, CA, pp: DOI: /ICNS Berntein, P.A. and N. Goodman, An algorithm for concurrency control and recovery in replicated ditributed databae. Tran. Databae Syt., 9: DOI: /

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