CODEWITHSUNDEEP
databaseconcurrencytransactionsdirtyread
AMAN GUPTA
AMAN GUPTA

Reputation: 141

Dirty read problem- updation in database after transaction doing dirty read commits

Suppose we have 2 transactions as T1, T2 with T2 doing dirty read on data modified by T1 and committing before T1. Now suppose T1 fails and is rolled back. My question is- Since T2 is committed, changes made by T2 are transferred from shared buffer to original database or not(Since I have read that changes made by a transaction are made permanent to original db once transaction commits)? And if they are transferred to original database, then how will T1 rollback and get previous value of data item (which was read dirty by T2)? By its buffer or original database?

Upvotes: 0

Views: 239

Answers (1)

TomC
TomC

Reputation: 2814

Unless you are specifically calling a dirty read by setting the isolation level, then this sort of problem simply can not happen. That is the whole idea of a transaction. T2 will be locked out of the row if T1 has updated it. If you are allowing dirty reads by setting set transaction isolation level read uncommitted then the handling of the data is up to you, usually by using a rowversion which your T2 checks hasnt changed before it commits.

Upvotes: 0

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