Que4.33. Explain concurrency control medium performed is distributed databases? Answer The following are concurrency control mechanisms in distributed database Two- phase commit protocol Two- phase commit protocol is designed to allow any party to repeal its part of the sale. Due to the demand for atomicity, if one part of a sale is abandoned also the whole sale must also be abandoned. Following are the two phase used in this protocol Phase 1( voting phase) 1. The match sends a canCommit? request to each of the actors in the sale. 2. When a party receives canCommit? request it replies with its vote( Yes or No) to the match. Before advancing Yes, it prepares to commit by saving objects in endlessstorage.However, If the vote is No. the party aborts incontinently. Phase 2( completion according to outgrowth of vote) 1. The match collects the votes( including its own). a. If there are no failures and all the votes are Yes the match decides to commit the sale and sends a doCommit request to each of the actors. else the match decides to repeal the sale and sends doAbort requests to all actors that suggested Yes. 2. Actors that suggested yea are staying for a doCommit or doAbort request from the match. When a party receives one of these dispatches it acts consequently and in the case of commit, makes a haveCommitted calls as evidence to the match. Moss concurrency control protocol 1. Moss concurrency control protocol for nested deals is grounded on the conception of upward heritage of cinches. 2. A sale can acquire a cinch on object O in some modeM. 3. Doing that, it holds the cinch in mode M until its termination. 4. Besides holding a cinch, a sale can retain a cinch in modeM. 5. When a subtransaction commits, its parent sale inherits its cinches and also retainsthem.However, it has the If a sale holds a cinch. right to pierce the locked object( in the corresponding mode). 6. still, the same isn’t true for retained cinches. 7. A retained cinch is only a place holder and indicates that deals outside the scale of the retainer can not acquire the cinch, but that descendants potentially can. 8. As soon as a sale becomes a retainer of a cinch, it remains a retainer for the cinch until it terminates. Que4.33. Explain directory system in detail. Answer 1. A directory is a table of information about some class of objects similar as persons. 2. Directories can be used to find information about a specific object, or in the rear direction to find objects that meet a certain demand. 3. In the networked world, the directories are present over a computer network, rather than in a physical( paper) form. 4. A directory system is enforced as one of further waiters, which service multiple guests. 5. guests use the operation programmer interface defined by the directory system to communicate with the directory waiters. Directory access protocols 1. Directory access protocol is a protocol that allows to pierce directory information through program. 2. Directory access protocols also define a data model and access control. 3. For case, web cybersurfers can store particular bookmarks and other cybersurfer settings in a directory system. A stoner can therefore pierce the same settings from multiple locales, similar as at home and at work, without having to partake a train system.
