July 2010
Intermediate to advanced
448 pages
12h 22m
English
Content preview from Physical Database Design
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214 CHAPTER 11 Query Execution Plans and Physical Design
3. Large data updates and/or additions will significantly change the statistics of the
database objects. These statistics are used by the query compiler during optimi-
zation and changes to them often result in new query execution plans. It is
common that performance problems can occur in a database system following
such large data changes for two reasons:
• The data has changed and the old query execution plan is suboptimal for
the new data within the system.
• The data has changed and the object statistics for one or more objects refer-
enced in the query were updated, resulting in the selection of a new query
execution plan that happens to be suboptimal due to poor choices by the
query compiler ...
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