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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, requesting an update with table-level locking denies
access to the table to all users except those using Dirty Read isolation.
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 while other users need access to the table, row-level locking is
appropriate. Table-level locking is only appropriate if the table is 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.