Kumar Kambam’s OBIEE Blog

Intelligence on Oracle Business Intelligence

OBIEE Cache is enabled, but why is the query not cached?

Repeatedly customers pose the question – OBIEE cache is enabled, but why is the query not cached? The reason why the queries are not cached can be of many reasons. Some of the reasons are:

Non-cacheable SQL function: If a request contains certain SQL functions, OBIEE will not cache the query. The functions are CURRENT_TIMESTAMP, CURRENT_DATE, CURRENT_TIME, RAND, POPULATE. OBIEE will also not cache queries that contain parameter markers.

Non-cacheable Table: Physical tables in the OBIEE repository can be marked ‘non-cacheable’. If a query makes a reference to a table that has been marked as non-cacheable, then the results are not cached even if all other tables are marked as cacheable.

 

Query got a cache hit: In general, if the query gets a cache hit on a previously cached query, then the results of the current query are not added to the cache. Note: The only exception is the query hits that are aggregate “roll-up” hits, will be added to the cache if the nqsconfig.ini parameter POPULATE_AGGREGATE_ROLLUP_HITS has been set to Yes.

Caching is not configured: Caching is not enabled in NQSConfig.ini file.

 

Result set too big: The query result set may have too many rows, or may consume too many bytes. The row-count limitation is controlled by the MAX_ROWS_PER_CACHE_ENTRY nqsconfig.ini parameter. The default is 100,000 rows. The query result set max-bytes is controlled by the MAX_CACHE_ENTRY_SIZE nqsconfig.ini parameter. The default value is 1 MB. Note: the 1MB default is fairly small. Data typically becomes “bigger” when it enters OBIEE. This is primarily due to Unicode expansion of strings (a 2x or 4x multiplier). In addition to Unicode expansion, rows also get wider due to : (1) column alignment (typically double-word alignment), (2) nullable column representation, and (3) pad bytes.

 

Bad cache configuration: This should be rare, but if the MAX_CACHE_ENTRY_SIZE parameter is bigger than the DATA_STORAGE_PATHS specified capacity, then nothing can possibly be added to the cache.

 

Query execution is cancelled: If the query is cancelled from the presentation server or if a timeout has occurred, cache is not created.

OBIEE Server is clustered: Only the queries that fall under “Cache Seeding” family are propagated throughout the cluster. Other queries are stored locally. If a query is generated using OBIEE Server node 1, the cache is created on OBIEE Server node 1 and is not propagated to OBIEE Server node 2

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January 19, 2009 Posted by | OBIEE Install and Config | , , , , , | 1 Comment

OBIEE Performance Tuning Tip – Turn off Query Logging

 

Though query logging has immeasurable development value, do not use this for regular production users as the runtime logging cost is extremely high. Every log item is flushed to the disk, which in turn hurts query response. Also, note that the query log files are not created on per user or query basis, there is only one query log per OBIEE server and it would have exclusive lock on the log file, which kills concurrent performance.

On the other hand, usage tracking has a very low runtime cost and is preferred to monitor the queries being used.

January 19, 2009 Posted by | OBIEE Performance Tuning | , , , | 3 Comments