OBIEE Caching Best Practices
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OBIEE Caching Best Practices
One of my recent discussions with a colleague on the caching strategy for OBIEE resulted in the following Best practices; Oracle BI Server is an Intelligent Query Engine that stores database hits in a cache file, this
cache file is stored on the BI server.
OBIEE Architectural Best Practice feature is to implement the caching mechanism by using the following methodology where in the configuration tags can be set in optimal fashion as follows:
Enable: turns caching on/off Data_Storage_Paths: defines location to store result files Metadata_File: defines location for cache metadata file Replace_Algorithm: for discarding entries if cache full Buffer_Pool_Size: buffer for caching metadata file Max_Rows_Per_Cache_Entry: upper limit on rows in result Max_Cache_Entry_Size: upper limit on size (#rows*#bytes/row) Max_Cache_Entries: upper limit on #of cached queries
The Following is an in detail Architectural configuration changes that can be implemented for OBIEE
Caching
Parameter: Enable Turns caching on/off
Best Practice: Set to YES if you want caching
Parameter: Data_Storage_Paths Defines the directory or directories to store cached result files Provide location and capacity DATA_STORAGE_PATHS = “d:\OracleBIData\nQSCache” 500 MB Least-recently-used cache is purged if full capacity
Best practice
o use dedicated drive(s): performance and reliability o use local disk (not a file share). (Not enforced)
o capacity should be significantly larger than value of Max_Cache_Entry_Size
Caveats to be kept in mind
o Disk space must exist (or bad things will happen) o Capacity of each location must not exceed 4 GB (2 GB before 7.7)
1. Parameter: Replace_Algorithm
Algorithm used to purge cache entries when the cache is full
“Full” is either:
1.
1. Max_Cache_Entries have been created 2. Less than Max_Cache_Entry_Size space is available
Removes cache entry that has not been accessed for longest time – not necessarily the oldest “created”
cache item
Only choice is LRU (least-recently-used)
1. Parameter: Buffer_Pool_Size
Defines the amount of memory for caching the cache metadata file.
Parameter does not affect correctness/behavior of cache – purely a performance setting
Best practice
Don’t change the default value. No/limited performance gains possible.
1. Parameter: Max_Rows_Per_Cache_Entry
Defines upper bound on number of rows in a cached result set
Prevent large or “runaway” queries from consuming too much cache
Query will run to completion, but if limit exceeded result will not be added to cache – event is not
logged
Set value to 0 if no limit is desired
Very large cache files are inefficient o stored in single file on disk o No indexes – full sequential scan to access
Best practice
o Define a non-zero value (less than 1,000,000 if possible)
o Max_Cache_Entry_Size is best place to define space limit
1. Parameter: Max_Cache_Entry_Size
Defines limit on size (#of bytes) of a cache entry
Used to prevent large cache entries from being created. Query will not be cached if exceeds this limit. No logging of exceeding limit.
Size: #of rows times #of bytes/row
#of bytes per row calculation:
o Unicode expansion (2x or 4x multiplier for char and varchar columns) o Column alignment overheads o Null value representation overhead
Cache is purged until Max_Cache_Entry_Size bytes are available
Best practice
o Set value to at most 10% of cache capacity (of smallest cache directory) o More effective limit than Max_Rows_Per_Cache_Entry or Max_Cache_Entries
Caveats
o Default value (1 MB) is fairly small. Many queries will hit this limit.