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What are the two disadvantages of implementing Query Caching?
A. Reduction in BI server processing time
B. Cache results being old
C. Storage space for cache
D. Increased network traffic
E. Needs a lot of administrators’ time
Correct Answer: BC
Explanation/Reference:
B: The problem with caching of any kind is how to deal with stale data. How you decide to deal with this depends on how time critical your business intelligence queries happen to be. OBIEE provides a wide variety of mechanisms for dealing with stale data. The cache can be purged automatically at intervals. Caching can be enabled selectively for individual physical tables, so that data in a frequently updated table is never cached. OBIEE provides a set of ODBC procedures that can be called when ETL processes complete to programmatically purge designated tables. But, by far the best way to selectively purge the cache is to use an event polling table. This table is populated by the client database whenever changes are made to any table (by an ETL process for a data warehouse or by a table-based trigger for an OLTP database). At specified intervals the BI Server polls this event polling table and deletes from its cache any query results that are dependent on the changed data.
Incorrect answers:
A: Processing time reduction is an advantage.
D: Network traffic decreases with caching.
E: Administration overhead is low.
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