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How does a database lock work?
Locking protocols are used in database management systems as a means of concurrency control. Multiple transactions may request a lock on a data item simultaneously. Hence, we require a mechanism to manage the locking requests made by transactions. Such a mechanism is called as Lock Manager.
How many locking levels are there in a database?
4 levels
The locking in a database can be done at 4 levels, which start with the database at the highest level and down via table and page to the row at the lowest level. This method of locking differentiates the locks based on their usage.
What causes database locks?
When one task is updating data on a page (or block), another task can’t access data (read or update) on that same page (or block) until the data modification is complete and committed. When multiple users can access and update the same data at the same time, a locking mechanism is required.
Are there different levels of locking in a database?
Database lock can be placed at different levels – on single row or multiple rows or on particular column or on entire table. This database locking at different level is known as locking granularity. Let us discuss them one by one below:
When to use table level locking in Oracle?
Table Level Locking : In this method, entire table will be locked. This will be useful when we need to update whole rows of the table. It will also be useful when we add/ remove some columns of the table where the changes affect entire table. Therefore, in Oracle this type of lock is also known as DDL lock.
Where does the locking hierarchy start in SQL Server?
SQL Server has introduced the locking hierarchy that is applied when reading or changing of data is performed. The lock hierarchy starts with the database at the highest hierarchy level and down via table and page to the row at the lowest level.
What does it mean when database file is locked?
File Level Locking : Here, entire database file will be locked. When we say database file, it may include whole table, or part of a table or part of multiple tables. Since file lock can include either whole or partial data from different tables, this type of lock is less frequent.