What happens in MySQL when 2 users update the same row at the same time?

Although it may seem like two users are updating the same row of data at the same time, the MySQL DBMS would prevent this from happening; instead one user’s update would go first and one would go second. The result would be that both updates would go through (just not at the same time).

What is the use of lock table query control concurrency?

Table Locks (TM) Table-level locks are primarily used to do concurrency control with concurrent DDL operations, such as preventing a table from being dropped in the middle of a DML operation. When a DDL or DML statement is on a table, a table lock is acquired. Table locks do not affect concurrency of DML operations.

What happens when two users are trying to update a database at the same time?

there will be occasions where two users will both read the same data into memory. User 1 will update the data and write those changes back to the database before user 2 does the same thing. Because if user 1 writes his data back into the database he will overwrite the changes made by user 2, causing them to be lost.

Which is better row level locking or table-level locking?

Row-level locking systems can lock entire tables if the WHERE clause of a statement cannot use an index. For example, UPDATES that cannot use an index lock the entire table. Row-level locking systems can lock entire tables if a high number of single-row locks would be less efficient than a single table-level lock.

Does MySQL lock row for update?

FOR UPDATE reads the latest available data, setting exclusive locks on each row it reads. Thus, it sets the same locks a searched SQL UPDATE would set on the rows.

What is row lock in MySQL?

If the tables use InnoDB, MySQL automatically uses row level locking so that multiple transactions can use same table simultaneously for read and write, without making each other wait. Row level locking also can be obtained by using SELECT FOR UPDATE statement for each rows expected to be modified.

What is shared lock in SQL Server?

A shared lock reserves a resource (page or row) for reading only. Other processes cannot modify the locked resource while the lock remains. On the other hand, several processes can hold a shared lock for a resource at the same time—that is, several processes can read the resource locked with the shared lock.

How does SQL Server handle concurrent updates?

In optimistic concurrency control, users do not lock data when they read it. When a user updates data, the system checks to see if another user changed the data after it was read. If another user updated the data, an error is raised. Typically, the user receiving the error rolls back the transaction and starts over.

How do you handle concurrent updates?

Usually, there are two ways to manage concurrent updates on resources:

1. Pessimistic concurrency control – This implies that the service locks the resource so that a client cannot updated it.
2. Optimistic concurrency control – This implies that a client first obtains a token for the update operation.

Which method is used to address conflicts with the concurrent access or modification of data that can occur with a multi user system?

Though for any practical Database, it would have a mix of READ and WRITE operations and hence the concurrency is a challenge. DBMS Concurrency Control is used to address such conflicts, which mostly occur with a multi-user system.

What is row level locking?

Row-level locking means that only the row that is accessed by an application will be locked. Hence, all other rows that belong to the same page are free and can be used by other applications. The Database Engine can also lock the page on which the row that has to be locked is stored.

What is table level locking and row level locking What is optimistic locking and pessimistic locking?

In SQL Server, the Repeatable Read isolation level is implemented using locking. If you read a row, you obtain a shared lock on that row, causing other transactions attempting to update the row to block until you commit or roll back your transaction. This behavior is very similar to pessimistic locking.