Interstage Shunsaku Data Manager Application Development Guide - Microsoft(R) Windows(R) 2000/ Microsoft(R) Windows Server(TM) 2003 - - UNIX -

5.1.5 Controlling Transaction Concurrency

When multiple transactions that are running at the same time manipulate the same data, appropriate adjustments must be performed to prevent contradictions and inconsistencies from occurring. Shunsaku performs this control automatically according to the following rules:

• Lookup and updating operations with respect to the same XML document operate simultaneously. One operation will not force the other operation to wait.
• An error will occur if an attempt is made to update an XML document that is being updated by another transaction that has not yet completed.
• An XML document that is referenced by one application may sometimes be updated and committed by another transaction. In such cases, if the application references the same XML document again, the result will be different from what it was previously. This is true even if the application that referenced the XML document is currently executing a transaction.
  In other words, regardless of whether a transaction is running, referencing the same XML document multiple times may result in different data being seen each time.
• If a search is performed twice using the same search expression while one transaction is running, and another transaction adds and commits data that matches that search condition between those two searches, the second search result will include one or more XML documents that are not contained in the first search result.

[Figure: Transaction for guaranteeing the integrity of data]

The following table shows if a conflict will occur when two concurrent transactions access the same XML document.

	Search	Add	Delete	Update
Search		-
Add	-	-	-	-
Delete		-	X	X
Update		-	X	X

: No conflict. Operations will be executed simultaneously.
X : Conflict. The operation that was executed later will generate an error.
- : No such situation will occur.

If a commit process and a search take place simultaneously, the search may use any partial results that have been committed by transactions that are performing the commit process.