System Recovery
- There can be any case in database system like any computer system when database failure happens.
- So data stored in the database should be available all the time whenever it is needed.
- Database recovery means recovering the data when it get deleted, hacked or damaged accidentally.
- So, database recovery techniques in DBMS are given below.
- Crash recovery:
- DBMS may be an extremely complicated system with many transactions being executed each second.
- If it fails or crashes amid transactions, it’s expected that the system would follow some style of rule or techniques to recover lost knowledge.
- Classification of failure:
- To see wherever the matter has occurred, we tend to generalize a failure into numerous classes, as follows:
- Transaction failure
- System crash
- Disk failure
- Transaction failure:
- A transaction needs to abort once it fails to execute or once it reaches to any further extent from wherever it can’t go to any extent further.
- This is often known as transaction failure wherever solely many transactions or processes are hurt. The reasons for transaction failure are:
- Logical errors
- System errors
- Logical errors: Where a transaction cannot complete as a result of its code error or an internal error condition.
- System errors: Wherever the information system itself terminates an energetic transaction as a result of the DBMS isn’t able to execute it, or it’s to prevent due to some system condition. to Illustrate, just in case of situation or resource inconvenience, the system aborts an active transaction.
- System crash:
- There are issues − external to the system − that will cause the system to prevent abruptly and cause the system to crash.
- For instance, interruptions in power supply might cause the failure of underlying hardware or software package failure.
- Examples might include OS errors.
- Disk failure:
- In the early days of technology evolution, it had been a typical drawback wherever hard-disk drives or storage drives accustomed to failing oftentimes.
- Disk failures include the formation of dangerous sectors, unreachability to the disk, disk crash or the other failure, that destroys all or a section of disk storage.
Tags:
DBMS
