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Difference between Dirty, commited ,phantom,repeatable
reads?
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Answer / bawa
- Dirty read—Dirty reads occur when one transaction reads data that has been written but not yet committed by another transaction. If the changes are later rolled back, the data obtained by the first transaction will be invalid.
- Nonrepeatable read—Nonrepeatable reads happen when a transaction performs the same query two or more times and each time the data is different. This is usually due to another concurrent transaction updating the data
between the queries.
- Phantom reads—Phantom reads are similar to nonrepeatable reads. These occur when a transaction (T1) reads several rows, and then a concurrent transaction (T2) inserts rows. Upon subsequent queries, the first transaction (T1) finds additional rows that were not there before.
| Is This Answer Correct ? | 29 Yes | 2 No |
Check the following link for differences:
http://sqlwithmanoj.wordpress.com/2011/07/20/dirty-reads-and-phantom-reads/
| Is This Answer Correct ? | 4 Yes | 1 No |
Answer / sknkarthik
dirty read allow a row changed by one transation to be read
by another transaction before any changes have been commited.
non repeatable read is whre one transaction chage a row
another transaction alter or delete the row then the 1st
transacton reread the row with the different value in the
second time.
phantom read is whre one transcation read the row that
satisfied the where condiotion the the 2nd transcation
insert the row with the where condiotion then the 1st
transaction reread the satisfied the where condition get the
phantom row in the second time
| Is This Answer Correct ? | 8 Yes | 8 No |
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