Database Access using Advanced Business Application Programming (ABAP)
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by Arindam Ghosh
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Lock Mechanisms

When the database system receives change statements (INSERT, UPDATE, MODIFY, DELETE) from a program, it automatically sets database locks. Database locks are locks on the database entries affected by statements to prevent problems. Since the lock mechanism uses a, lock flag in the entry, you can only set a lock for an existing database entry. After each database commit, these flags are automatically deleted. This means that database locks can never be set for longer than a single database LUW, a single dialog step in an R/3 application program.

Therefore, physical locks in the database system are insufficient for the requirements of an R/3 transaction. Locks in the R/3 system must remain set for the duration of a whole SAP LUW, that is, over several dialog steps. They must also be capable of being handled by different work processes and application servers. As a result, each lock must apply on all servers in that R/3 system.

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