In this method log files are backed up at regular intervals, and database is backed up once in a week. So seeing these log files, database can be recovered. These log files will have all the information about the transaction being made. Hence only the log files are backed up at regular intervals. As the database grows, it is an overhead to backup whole database.If there is any failure, the data would be copied from these tapes to bring the database up. In the second method, database is copied to memory devices like magnetic tapes and kept at secured place.The user will not know that there was a failure. In this case, as soon as there is a failure of current database, system automatically switches to the remote database and starts functioning. It can be backed up online where the data is updated at current and remote database simultaneously.
PDF BASICS OF DATA RECOVERY OFFLINE
This remote database can be updated manually called offline backup. This database is periodically updated with the current database so that it will be in sync with data and other details. Remote Backup: – Database copy is created and stored in the remote network.There are three methods used to back up the data in the secondary memory, so that it can be recovered if there is any failure. We have to think of some alternative solution for this because we cannot afford for loss of data in huge database. What happens to the data stored in it? All the data are lost and we cannot recover. Suppose the secondary memory itself crashes. We can have checkpoints created at several places so that data is copied to the database.We can recover the data till the point it is last copied to the database. So in case of any failure, we will not lose all the data. We can create a copy of primary memory in the database with all the logs and buffers, and are copied periodically into database.In such cases, we can follow any one the following steps so that data in the primary memory are not lost. What happens if the primary memory crashes? All the data in the primary memory is lost and we cannot recover the database. Fetching the record from primary memory is always faster than secondary memory. When a query is fired, the database first fetches in the primary memory for the data, if it does not exist there, then it moves to the secondary memory to fetch the record. It stores all the recent transactions and the results too. Primary memory storage devices – RAM is a volatile memory which stores disk buffer, active logs, and other related data of a database.
In a computer system we have primary and secondary memory storage. This is because, in case of any crash and data loss, data can be recovered from other copies. In this case, copies of same non volatile memories are stored at different places.
these memories are designed to withstand system crashes. E.g.: – Flash memory, hard disk, magnetic tapes etc. Non-Volatile memory: – These are secondary memories and are huge in size, but slow in processing.these memories cannot endure system crashes- data in these memories will be lost on failure. These memories can store only small amount of data, but they are very fast. Volatile Memory: – These are the primary memory devices in the system, and are placed along with the CPU.It is mainly divided into two categories: Storage structure is the memory structure in the system. Recovery with Concurrent Transactions Storage Structure.There are two methods of creating this log files and updating the database.We can recover the database in two methods:.We can conclude from above example that.
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