Transaction 1 commits its changes, and Transaction 2 is able to read the updated value of the row.Therefore, Transaction 2 is blocked until Transaction 1 commits its changes. Transaction 2 begins and wants to read the value of the same row, but the value has not been committed by Transaction 1 yet.Transaction 1 begins and updates the value of a certain row in a table. Here’s an example of how the READ COMMITTED isolation level works: This means that a transaction cannot read data that is still in the process of being modified by other transactions. The READ COMMITTED isolation level in PostgreSQL ensures that a transaction can only read data that has been committed by other transactions. It is important to note that in PostgreSQL, the default isolation level is READ COMMITTED, and it is generally not recommended to use READ UNCOMMITTED in production environments as it can lead to data inconsistencies and other issues. In this example, the transaction starts with the BEGIN statement, sets the isolation level to READ UNCOMMITTED, then selects all rows from the “mytable” table, and finally commits the transaction. Here’s an example of how READ UNCOMMITTED isolation level can be used in PostgreSQL: This means that the transaction can read dirty data, which can lead to non-repeatable reads and phantom reads. The READ UNCOMMITTED isolation level in PostgreSQL allows a transaction to read rows that have been modified by other transactions, but not yet committed. PostgreSQL Transaction Isolation Levels explained with an example This can lead to dirty reads and other inconsistencies. Read Uncommitted: This isolation level is not recommended, as it allows a transaction to see data that has been modified by other transactions but not yet committed. Serializable: This isolation level guarantees that a transaction will only see data that has been committed by other transactions before the current transaction began, and that any data read or modified by the current transaction will not be changed by other transactions until the current transaction is committed.Repeatable Read: This isolation level ensures that a transaction will only see data that has been committed by other transactions before the current transaction began, and that any data read by the current transaction will not be changed by other transactions until the current transaction is committed. It guarantees that a transaction will only see data that has been committed by other transactions before the current transaction began.
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