IBM 000-8697 Manual de usuario descargar pdf (Pagina 449)

100

101

How to Improve Performance 5-9

Eliminate User-Created Resource Bottlenecks

■ Do not perform mass updates on frequently accessed tables.

During an update, the row must be locked. Mass updates to a table

are best performed with table-level locking to reduce locking over-

head.However,requestinganupdatewithtable-levellockingdenies

accesstothetabletoallusersexceptthoseusingDirtyReadisolation.

Users should balance their desire to perform a large transaction

against the effect their work has on concurrency. Mass updates

should always be timed for less active times. If the update must

occur whileother users need access to the table,row-level locking is

appropriate.Table-levellockingis only appropriateifthetableis not

needed by other users during the transaction.

■ Consider the access problems that might result before you specify a

restrictive isolation level in an application.

Users should be aware that the isolation or locking level that they

select for their processing can affect other users. Isolation and lock-

ing levels should be selected to be consistent with the concurrency

needs of the complete OnLine environment.

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