B+ tree locking is a method of concurrency control used in database systems to ensure consistency and correctness in the face of multiple concurrent transactions accessing the same data. In B+ tree locking, locks are acquired on nodes in the B+ tree data structure that stores the database index, rather than on individual data records.
Here is an example to illustrate how B+ tree locking works. Suppose we have a database table that stores information about bank accounts, and we want to allow multiple concurrent transactions to access and modify this table.
To implement B+ tree locking, we first create a B+ tree index on the 'account number' column of the table. This index organizes the account numbers in a sorted order, and allows for efficient searching and retrieval of records based on account number.
When a transaction wants to read or modify a record in the table, it first acquires a shared lock on the node of the B+ tree that corresponds to the account number it is interested in. This ensures that no other transaction can modify or delete that node while the first transaction is still using it.
If the transaction wants to modify a record, it must acquire an exclusive lock on the node. This ensures that no other transaction can modify or delete any record within that node while the first transaction is still making changes.
Once the transaction has finished using the node, it releases its lock, allowing other transactions to acquire locks on the same node and access the same data.
B+ tree locking is an effective method of concurrency control because it allows multiple transactions to access the same data without interfering with each other, while also ensuring that changes to the data are made in a consistent and correct manner. However, it can also be complex to implement and may require significant overhead in terms of locking and unlocking nodes in the B+ tree.
