SYM 400 Topic 6 DQ 1
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Information Systems
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Nov 24, 2024
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What are the pros and cons of pessimistic concurrency in relation to optimistic concurrency? What are the pros and cons of explicit transactions in relation to implicit transactions, and vice versa? Support your rationale.
Hello professor Blasius and class,
Pessimistic concurrency is called pessimistic because the system assumes that two or more users are going to need to access the same record at the same time and prevents this from occurring by locking the record. Optimistic concurrency control assumes that while conflicts can occur they will be rare. Instead of locking the record every single time it looks for instances the two users have tried to access the same record at the same time before in the past. Pessimistic concurrency can be beneficial if there are several updates and a high likelihood of several users trying to access the same record at the same time. On the con side it can slow down productivity and add time since one user has to wait while the other user makes changes. Optimistic concurrency is beneficial for records that are not highly important or sensitive. If one user is updating a record and has not yet committed the transaction the other user might see the outdated information and version number. In an explicit transaction the user creates lines specifying the beginning and end of the transaction. This involves the user using a command like “BEGIN TRANSACTION” to start the transaction, and “COMMIT (OR ROLLBACK) TRANSACTION” to complete it. For implicit transactions the user is not required to use the command BEGIN TRANSACTION, but instead can input SELECT, INSERT, CREATE USER, and then uses the COMMIT TRANSACTION command.
References
UNICOM Systems, Inc. Support. (n.d.). SQL Guide : Managing transactions : Concurrency control and locking : PESSIMISTIC vs. OPTIMISTIC concurrency control. https://support.unicomsi.com/manuals/soliddb/7/index.html#page/SQL_Guide/
5_ManagingTransactions.06.4.html
Zacks, T. (2021, August 6). SQLServer: What is implicit & explicit transaction. learn.microsoft.com. https://learn.microsoft.com/en-us/answers/questions/504480/sqlserver-what-is-implicit-explicit-
transaction
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