A dirty read is a situation in a database system where a data item that has been updated by transaction A and not yet committed is read by transaction B. If a transaction B performs an update and commits the changes, it can cause a violation of some transaction rules in data management. Phantom read is a case where a certain transaction executes a query and obtains query results. There are chances that some of the data items are concurrently being changed by another transaction and making them not qualify for this query. This can apply for both insertion and deletion of data items hence causing concurrency anomaly.
Data Violations Caused by Dirty Read and Phantom
Data concurrency
This refers to the ability of the database to allow the execution of multiple transactions concurrently without affecting the outcome of each transaction. Concurrency anomalies occur as a result of dirty reads and phantom reads. To avoid or prevent concurrency anomalies as a result of dirty read, transaction locks should be employed to bring about concurrency control and not allow a write operation to a data item that is already under a read operation by a different transaction.
Data consistency
This refers to a context of databases where only valid data should be written to the database and transactions that violate the consistency rules cannot be executed, and in case an execution violating the rules occurs, the entire transaction should be rolled back, and the database then restored to the original state. Therefore, no changes made to a data item should be isolated from the other transactions and should remain visible to avoid dirty and phantom reads. Data concurrency control measures should be employed to avoid the violation of these data rules.