Contents

Revision on database
Some of DBMS engines
The SQL language
Relational algebra and translating SQL queries to relational algebra
Selection, Projection, Rename Operation
UNION Operation , Intersection, Cross product, Set Diffrence
Natural Join, ............

Recovery Techniques

January 8, 2020

Transaction Manager: Accepts transaction commands from an application, which tell the transaction manager when transactions begin and end, as well as information about the expectations of the application. The transaction processor performs the following tasks:
Logging: In order to assure durability, every change in the database is logged separately on disk.
Log manager:
initially writes the log in buffers and negotiates with the buffer manager to make sure that buffers are written to disk at appropriate times. Recovery Manager:
will be able to examine the log of changes and restore the database to some consistent state.
The Purpose of Database Recovery:
To bring the database into the last consistent state, which existed prior to the failure.
To preserve transaction properties (Atomicity & Durability).
The recovery manager of a DBMS is responsible to ensure Atomicity by undoing the action of transaction that do not commit
Durability by making sure that all actions of committed transaction survive system crash.

IV. Data Caching Data items to be modified are first stored into database cache by the Cache Manager (CM) and after modification they are flushed (written) to the disk When DBMS request for read/write operation on some item It checks the requested data item is in the cache or not If it is not, the appropriate disk block are copied to the cache. If the cache is already full, some buffer replacement policy can be used. Like Least recent used (LRU) FIFO While replacing buffers, first of all the updated value on that buffer should be saved on the appropriate block in the database

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