Friday, November 1, 2019

Information on DBMS of Microsoft SQL Essay Example | Topics and Well Written Essays - 500 words

Information on DBMS of Microsoft SQL - Essay Example Other users can read and modify the record anytime while the main user is performing operations on the output displayed. Shared locks allow concurrent users to read data. They are released when the data is read. Exclusive locks do not allow concurrent transactions on the data. Update locks are used to prevent deadlock where if a transaction updates data, it becomes exclusive lock else shared lock. Intent locks signify which granular level the SQL server wants to acquire lock. This technique uses logs to record the updates. The update log defines a single write on the table. This log contains the identifier for the transaction, the data item, the old and the new value updated. Once a transaction performs a write, log record for it is created. This log helps in recovering the data. This method also uses log to record the data but the write action is deferred until the transaction is partially committed. Once the transaction partially commits, the data on the log is executed in deferred writes. In case the system crashes, the data on the log is ignored. Two page tables (Current page table and shadow page table) are maintained in this technique. Each time a write occurs in the current page, it points to a page in the disk and a copy of it is made in the shadow table. When a system crashes, data is recovered from shadow table. It is a point where all the transactions are updated to reflect the data in the log. This updates the data properly to all the transactions ensuring no conflicts occur. This checkpoint ensures that all the data is committed in the SQL

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