On Serializability of Multidatabase Transactions Through Forced Local Conflict

Wright State University CORE Scholar The Ohio Center of Excellence in Knowledge- Kno.e.sis Publications Enabled Computing (Kno.e.sis) 4-1991 On Serializability of Multidatabase Transactions through Forced Local Conflict Dimitrios Georgakopoulos Marek Rusinkiewicz Amit P. Sheth Wright State University - Main Campus, [email protected] Follow this and additional works at: https://corescholar.libraries.wright.edu/knoesis Part of the Bioinformatics Commons, Communication Technology and New Media Commons, Databases and Information Systems Commons, OS and Networks Commons, and the Science and Technology Studies Commons Repository Citation Georgakopoulos, D., Rusinkiewicz, M., & Sheth, A. P. (1991). On Serializability of Multidatabase Transactions through Forced Local Conflict. Proceedings of the Seventh International Conference on Data Engineering, 314-323. https://corescholar.libraries.wright.edu/knoesis/845 This Conference Proceeding is brought to you for free and open access by the The Ohio Center of Excellence in Knowledge-Enabled Computing (Kno.e.sis) at CORE Scholar. It has been accepted for inclusion in Kno.e.sis Publications by an authorized administrator of CORE Scholar. For more information, please contact library- [email protected]. ON SERIALIZABILITY OF MULTIDATABASE TRANSACTIONS THROUGH FORCED LOCAL CONFLICTS Dimitrios Georgakop oulos and Marek Rusinkiewicz Amit Sheth Department of Computer Science Bellcore University of Houston Ho es Lane Houston TX Picataway NJ Abstract trievals and to preserve the global consistency in the presence of multidatabase up dates These ob jectives The main diculty in enforcing global serializabilityin are more dicult to achieve in MDBSs than in homo amultidatabase environment lies in resolving indirect geneous distributed database systems b ecause in ad transitive conicts b etween multidatabase transac dition to the problems caused by data distribution and tions Indirect conicts intro duced by lo cal transac replication that all distributed database systems have tions are dicult to resolve b ecause the the b ehav to solve transaction management in MDBSs must also ior or even the existence of lo cal transactions is not cop e with heterogeneity and autonomy of the partici known to the multidatabase system Toovercome pating LDBSs these problems we prop ose to incorp orate additional In a multidatabase environment the serializability data manipulation op erations in the subtransactions of of lo cal schedules is by itself not sucienttomain eachmultidatabase transaction We show that if these tain the multidatabase consistency To assure that op erations create direct conicts b etween subtransac global serializability is not violated lo cal schedules tions at each participating lo cal database system indi must b e validated bytheMDBSHowever the lo cal rect conicts can b e resolved even if the multidatabase serialization orders are neither rep orted by the lo cal system is not aware of their existence Based on this database systems nor can they b e determined bycon approachweintro duce a multidatabase transaction trolling the submission of the global subtransactions management metho d that requires the lo cal database or observing their execution order To determine the systems to ensure only lo cal serializabilityThepro serialization order of the global transactions at each p osed metho d and its renements do not violate the LDBS the MDBS must deal not only with direct con autonomy of the lo cal database systems and guaran icts that may exist b etween the subtransactions of tee global serializabilityby preventing multidatabase multidatabase transactions but also with the indirect transactions from b eing serialized in dierentways at conicts that may b e caused by the lo cal transactions the participating database systems Since the MDBS has no information ab out the exis tence and b ehavior of the lo cal transactions deter mining if an execution of global and lo cal transactions Intro duction is globally serializable is dicult Several solutions have b een prop osed in the litera A Multidatabase System MDBS is a facilitythat ture to deal with this problem however most of them supp orts global applications accessing data stored in are not satisfactory The main problem with the ma multiple databases It is assumed that the access to jority of the prop osed solutions is that they do not these databases is controlled by autonomous and p os provide a way of assuring that the execution order of sibly heterogeneous Local Database Systems LDBSs global transactions whichcanbecontrolled bythe The MDBS architecture allows local transactions and MDBS is reected in their lo cal serialization order global transactions to co exist Lo cal transactions are pro duced by the LDBSs In this pap er wesolve this submitted directly to a single LDBS while the multi problem byintro ducing a technique which disallows database global transactions are channeled through schedules in which a global transaction G is executed i the MDBS interface The ob jectives of multidatabase and committed by some LDBS b efore another transac transaction management are to avoid inconsistentre tion G but their lo cal serialization order is reversed j Our solution do es not violate the lo cal autonomyand Current address GTE Lab oratories Waltham MA lo cal transactions and the indirect conicts they may is applicable to all LDBSs that guarantee lo cal serial cause For example since the MDBS has no informa izabilityWe also discuss the class of schedules and tion ab out the lo cal transaction T it cannot detect schedulers in which the serialization order of each the indirect conict b etween G and G at LDBS Al transaction can b e determined bycontrolling its ex though b oth lo cal schedules are serializable the sched ecution and commitment We show that if the partici ule is globally nonserializable ie there is no global pating LDBSs use one of the many common schedulers order involving G G and T that is compatible with that b elong to this class multidatabase transaction b oth lo cal schedules management is simplied The pap er is organized as follows In Section we G G identify the diculties in maintaining global serializ ability in MDBSs and review the related work In I Section weintro duce the concept of a subtransac tion ticket and prop ose the Optimistic Ticket Method OTM for multidatabase transaction management To guarantee global serializability OTM requires that LD B S a LD B S b c the LDBSs ensure lo cal serializabilityWe also discuss CO the Implicit Ticket Method ITM a renementofthe C OTM which reduces the overhead of OTM but works C C only for a sub class of the participating LDBSs Section C FinallyinSectionwe summarize our results C T LDBS w ar aieG G G G Problems in maintain LDBS w br bw cr c ie G T G T G G T ing global serializabilityand Figure Serial execution of multidatabase transac related work tions may violate serializability Many algorithms that have b een prop osed for trans In the early work in this area the problems caused action management in distributed systems are not di by indirect conicts were not fully recognized In their rectly applicable in MDBSs b ecause of the p ossibil early pap er Gligor and Pop escuZeletin stated ity of indirect conicts caused by the lo cal transac thataschedule of multidatabase transactions is cor tions To illustrate this p oint let us consider Figure rect if multidatabase transactions have the same rel which depicts twomultidatabase transactions G and ative serialization order at each LDBS they directly G and a lo cal transaction T If a transaction G i conict Breitbart and Silb erschatz haveshown reads a data item awe drawanarcfroma to G An i that the ab ove correctness criterion is insucientto arc from G to a denotes that G writes a In our ex i i guarantee global serializability in the presence of lo cal ample the global transactions have subtransactions in transactions They proved that the sucient condition b oth LDBSs In LDBS G writes a and G reads it for the global consistency requires the multidatabase Therefore G and G directly conict in LDBS and transactions to have the same relative serialization or the serialization order of the transactions is G G der in all sites they execute The solutions to the prob In LDBS G and G access dierent data items ie lem of concurrency control in MDBSs that havebeen G reads b and G writes c Hence there is no di prop osed in the literature can b e divided into several rect conict b etween G and G in LDBS However groups since the lo cal transaction T writes b and and reads c G and G conict indirectly in LDBS This in Observing the execution of the global trans direct conict is caused by the presence of the lo cal actions at each LDBS The execution order transaction T In this case the serialization order of of global transactions do es not determine their rela the transactions in LDBS b ecomes G T G tive serialization order at each LDBS For example In a multidatabase environment the MDBS has con at LDBS in Figure the global transaction G is trol over the execution of global transactions and the executed b efore G but G precedes G in the lo cal op erations they issue Therefore the MDBS can de serialization order there To determine lo cal conicts tect direct conicts involving global transactions such between transactions Logar and Sheth prop osed as the conict b etween G and G at LDBS in Fig using the commands of the lo cal op erating system and

Load more