why does the phantom 3 advanced get better range than the phantom 4?

Non-repeatable reads: read COMMITTED data from an UPDATE query from another transaction.Dirty reads: read UNCOMMITED data from another transaction.

So, while the Non-Repeatable Read applies to a single row, the Phantom Read is about a range of records which satisfy a given query filtering criteria. If Bob’s re-reads the post_comment records having the post_id column value equal to 1, he will observe a different version of this result set.Alice adds a new post_comment record which is associated with the post row having the identifier value of 1.Bob’s reads all the post_comment records associated with the post row with the identifier value of 1.The Phantom Read anomaly can happen as follows: If Bob’s re-reads the post record, he will observe a different version of this table row.Alice commits her database transaction.Alice modifies the title of a given post record to the value of ACID.Bob’s reads the post record and title column value is Transactions.Alice and Bob start two database transactions.The Non-Repeatable Read anomaly looks as follows: In Oracle, transaction A could also issue a SELECT FOR UPDATE, then transaction B cannot change the row until A is done. You can have non-repeatable reads, so if that is a problem, you may want to have an isolation level that prevents that. In your example, you won't have a phantom read, because you select only from a single row (identified by primary key). There is a high cost to a 'better' isolation level (such as reduced concurrency). What isolation level you need depends on your application. In the above example,which isolation level to be used? Example: select sum(x) from table will return a different result even if none of the affected rows themselves have been updated, if rows have been added or deleted. Phantom read: All the rows in the query have the same value before and after, but different rows are being selected (because B has deleted or inserted some).Non-repeatable read: The A row that user A has queried has a different value the second time.In between, User B runs a transaction and commits.From Wikipedia (which has great and detailed examples for this):Ī non-repeatable read occurs, when during the course of a transaction, a row is retrieved twice and the values within the row differ between reads.Ī phantom read occurs when, in the course of a transaction, two identical queries are executed, and the collection of rows returned by the second query is different from the first.

Why does the phantom 3 advanced get better range than the phantom 4?