What is lock mode in DB2?
What is lock mode in DB2?
Of the non-intent locking modes, DB2 can use NS, S and U locks for read requests. The NS locks are only used at the row level for applications using CS and RS isolation levels. DB2 uses the non-intent mode locks Exclusive (X), Super exclusive (Z) and Next Key Weak(NW) for write requests.
How many types of locks are there in DB2?
DB2 supports locking at four levels, or granularities: table space-, table-, page-, and row-level locking. DB2 also provides LOB locking for large objects (BLOBs, CLOBs, and DBCLOBs). Locks can be taken at any level in the locking hierarchy without taking a lock at the lower level.
What are locked attributes?
The only type of object that you can lock explicitly is a table. The database manager also sets locks on other types of resources, such as rows and table spaces.
What are the types of lock in database?
At the table level, there are five different types of locks:
- Exclusive (X)
- Shared (S)
- Intent exclusive (IX)
- Intent shared (IS)
- Shared with intent exclusive (SIX)
Can buffer be locked in database?
A form of enqueue locking is used to protect cached database blocks. For each buffer in the database buffer cache, there is a buffer header. The buffer headers constitute a fixed array in the permanent memory part of the shared pool….Buffer Locks.
| Parameter | Description |
|---|---|
| p2 | The block number of the database block in its file. |
What is cursor stability in DB2?
Cursor stability is the Db2 implementation of the SQL standard read committed isolation level. Under an RR isolation level all page locks are held until they are released by a COMMIT (or ROLLBACK), whereas with CS read-only page locks are released as soon as another page is accessed.
How many types of locks are there?
Although there are many types of locks, the four most common are padlocks, deadbolts, knob locks, and levers.
How does cursor work in Db2?
DB2 uses a cursor to make the rows, from the results table, available to the application program. A cursor identifies the current row of the results table. When you use a cursor, the program can retrieve each row sequentially from the results table until end-of-data (i.e the not found condition SQLCODE=100).
What is a read lock?
Acquiring a read lock ensures that a different transaction does not modify or delete a row while it is being read. Any number of transactions can acquire read locks on any row at the same time, so read locks are sometimes referred to as shared locks, or non-exclusive locks.
What is lock and types of lock?
Locks are of two kinds − Binary Locks − A lock on a data item can be in two states; it is either locked or unlocked. Shared/exclusive − This type of locking mechanism differentiates the locks based on their uses. If a lock is acquired on a data item to perform a write operation, it is an exclusive lock.
What are the two types of locks?
There are two types of lock:
- Shared lock: It is also known as a Read-only lock. In a shared lock, the data item can only read by the transaction.
- Exclusive lock: In the exclusive lock, the data item can be both reads as well as written by the transaction.
What is the difference between latch and lock?
A latch fastens a door, gate or window in position but does not provide security. A lock prevents anyone without a key from opening a door/gate/etc.
What is latchlocking in DB2?
Locking process is controlled by DB2’s IRLM (Inter System Resource Lock Manager). However, whenever practical, DB2 tries to lock pages without going to the IRLM. This type of lock is called a latch. Data is actually stored in a structure known as table space.
How many uncommitted rows must be locked in DB2?
Consequently, if only 2 of 10 rows on a page contain uncommitted data, Db2 must lock the entire page when using page lock. However, Db2 but might ask for locks on only the two uncommitted rows when using row-level locks.
What is locksize (any) in DB2?
When a table space is defined or altered, the LOCKSIZE clause specifies a default lock size. When the LOCKSIZE (ANY) option is used, DB2 selects the optimum lock size for each processing situation. Lock hierarchy is as follows:
How do you lock a page in DB2?
In data sharing, when a DB2 member determines that a page latch is necessary (say, during a row insert), it sends a Page P-Lock request to a data store called the Lock Structure. This data store exists in a centralized area called the Coupling Facility, which is accessible by all DB2 members.