How deadlock is fixed in Oracle?
Resolving Oracle deadlocks
- Tune the application – Single-threading related updates and other application changes can often remove deadlocks.
- Add INITRANS – In certain conditions, increasing INITRANS for the target tables and indexes(adding slots to the ITL) can relieve deadlocks.
How to avoid Oracle deadlock?
LOCK IN SHARE MODE ), try using a lower isolation level such as READ COMMITTED . When modifying multiple tables within a transaction, or different sets of rows in the same table, do those operations in a consistent order each time. Then transactions form well-defined queues and do not deadlock.
How do you check if there is a deadlock in Oracle?
In summary, the steps necessary to identify and rectify code causing deadlocks are:
- Locate the error messages in the alert log.
- Locate the relevant trace file(s).
- Identify the SQL statements in both the current session and the waiting session(s).
What causes Oracle deadlocks?
In a database, a deadlock is a situation in which two or more transactions are waiting for one another to give up locks. For example, Transaction A might hold a lock on some rows in the Accounts table and needs to update some rows in the Orders table to finish.
What is the difference between lock and deadlock in Oracle?
Deadlock occurs when one process is blocked and waiting for a second process to complete its work and release locks, while the second process at the same time is blocked and waiting for the first process to release the lock.
How can deadlock be removed?
A deadlock occurs when the first process locks the first resource at the same time as the second process locks the second resource. The deadlock can be resolved by cancelling and restarting the first process.
What is Initrans and Maxtrans in Oracle?
The INITRANS setting controls Initial Transaction Slots (ITLs). A transaction slot is required for any session that needs to modify a block in an object. For tables INITRANS defaults to 1 for indexes, 2. The MAXTRANS setting controls the maximum number of ITLs that a block can allocate (usually defaults to 255).
How do I view a blocked session?
Answer: You can query the dba_blockers and dba_waiters views to locate blocking sessions, but you can also get this information from v$lock and v$session. Also see these related notes on finding Oracle blocking sessions: Find blocking sessions with v$session. Find the data block for a blocking session.
What are locks and deadlocks?
A lock wait timeout results when one user gets a lock on some data and holds it while another user tries to access it. A deadlock happens when multiple lock waits happen in such a manner that none of the users can do any further work. For example, the first user and second user both lock some data.