0 votes 0 votes what is the difference between Vertical and Horizontal fragmentations. If Data objects replicas are stored at multiple number of sites, Explain how the lock will be acquired by a transaction on data objects Databases databases + – LavTheRawkstar asked Apr 14, 2017 LavTheRawkstar 2.2k views answer comment Share Follow See all 11 Comments See all 11 11 Comments reply Show 8 previous comments LavTheRawkstar commented May 1, 2017 reply Follow Share dear sir yes i got the answer for horizontal and vertical fragmentation. but i am still not getting If Data objects replicas are stored at multiple number of sites, Explain how the lock will be acquired by a transaction on data objects it is written so complex firstly tell for data objects replicas do we use Timestamp method or Lock based method or Optimistic Concurrency method or MultiVersion method? I believe we use Lock based method? so in Lock based we use only Shared and Exclusive lock so then how it will be implemented can you please take example and provide me exact answer for the question ? 0 votes 0 votes LavTheRawkstar commented May 3, 2017 reply Follow Share I am still waiting for reply dear sir 1 votes 1 votes Bikram commented May 4, 2017 reply Follow Share @LavTheRawkstar For data objects replicas we use Lock based method . In a relational data model when multiple copies are stored in different sites , it is called Replication . Replication : System maintains multiple copies of data, stored in different sites, for faster retrieval and fault tolerance purpose. Now those data is fragmented into different parts , called Fragmentation where Relation is partitioned into several fragments stored in distinct sites . Replication and fragmentation can be combined . Relation is partitioned into several fragments: system maintains several identical replicas of each such fragment. Now your question is how the lock will be acquired by a transaction on data objects which are replicated at multiple number of sites : Here we use Distributed Two Phase locking Algorithm . In a distributed system there are sites designated as lock managers. A lock manager controls lock acquisition requests from transaction monitors. In order to enforce co-ordination between the lock managers in various sites, at least one site is given the authority to see all transactions and detect lock conflicts. Depending upon the number of sites who can detect lock conflicts, distributed two-phase locking approaches can be of three types − Centralized two-phase locking − In this approach, one site is designated as the central lock manager. All the sites in the environment know the location of the central lock manager and obtain lock from it during transactions. Primary copy two-phase locking − In this approach, a number of sites are designated as lock control centers. Each of these sites has the responsibility of managing a defined set of locks. All the sites know which lock control center is responsible for managing lock of which data table/fragment item. Distributed two-phase locking − In this approach, there are a number of lock managers, where each lock manager controls locks of data items stored at its local site. The location of the lock manager is based upon data distribution and replication. 1 votes 1 votes Please log in or register to add a comment.