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Exclusive locks cannot be obtained when a record is already locked (exclusively or shared) by another entity. If lock requests for the same entity are queued, then once a shared lock is granted, any queued shared locks may also be granted. If an exclusive lock is found next on the queue, it must wait until all shared locks have been released.
or Rigorousness, or Rigorous scheduling, or Rigorous two-phase locking. To comply with strong strict two-phase locking (SS2PL), a transaction's read and write locks are released only after that transaction has ended (i.e., either committed or aborted). A transaction obeying SS2PL has only a phase 1 and lacks a phase 2 until the transaction has ...
In addition to shared (S) locks and exclusive (X) locks from other locking schemes, like strict two-phase locking, MGL also uses intentional "locks", which do not directly lock a node, but instead denote the existence, or intent to add, a lock of the specified type lower in the node hierarchy.
In databases and transaction processing the term Locks with ordered sharing comprises several variants of the two-phase locking (2PL) concurrency control protocol generated by changing the blocking semantics of locks upon conflicts. Further softening of locks eliminates thrashing.
To restate; every object (P) has a Timestamp (TS), however if transaction T i wants to Write to an object, and the transaction has a Timestamp (TS) that is earlier than the object's current Read Timestamp, TS(T i) < RTS(P), then the transaction is aborted and restarted. (This is because a later transaction already depends on the old value.)
A transaction Ti that inserts, updates or deletes a tuple ti in a relation r must update all indices to r and it must obtain exclusive locks on all index leaf nodes affected by the insert/update/delete; The rules of the two-phase locking protocol must be observed. [1] Specialized concurrency control techniques exist for accessing indexes. These ...
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lock contention: this occurs whenever one process or thread attempts to acquire a lock held by another process or thread. The more fine-grained the available locks, the less likely one process/thread will request a lock held by the other. (For example, locking a row rather than the entire table, or locking a cell rather than the entire row);