Editing Lock (computer science) (section)

== Lock compatibility table ==
Several variations and refinements of these major lock types exist, with respective variations of blocking behavior. If a first lock blocks another lock, the two locks are called ''incompatible''; otherwise the locks are ''compatible''. Often, lock types blocking interactions are presented in the technical literature by a ''Lock compatibility table''. The following is an example with the common, major lock types:

{| class="wikitable" style="text-align:center;"
|+Lock compatibility table
|-
! Lock type !! read-lock  !! write-lock
|-
! read-lock
| '''✔''' || '''X'''
|-
! write-lock
| '''X''' || '''X'''
|}

*'''✔''' indicates compatibility
*'''X''' indicates incompatibility, i.e., a case when a lock of the first type (in left column) on an object blocks a lock of the second type (in top row) from being acquired on the same object (by another transaction). An object typically has a queue of waiting requested (by transactions) operations with respective locks. The first blocked lock for operation in the queue is acquired as soon as the existing blocking lock is removed from the object, and then its respective operation is executed. If a lock for operation in the queue is not blocked by any existing lock (existence of multiple compatible locks on a same object is possible concurrently), it is acquired immediately.
'''Comment:''' In some publications, the table entries are simply marked "compatible" or "incompatible", or respectively "yes" or "no".<ref>{{Cite web |date=2018-03-07 |title=Lock Based Concurrency Control Protocol in DBMS |url=https://www.geeksforgeeks.org/lock-based-concurrency-control-protocol-in-dbms/ |access-date=2023-12-28 |website=GeeksforGeeks |language=en-US}}</ref>