Administering and Monitoring Analysis Services - SQL Server Analysis Services 2012 Cube Development - page 268

The <Memory><LowMemoryLimit> property controls the point—amount of
memory used by SSAS—at which the cleaner thread becomes actively engaged in
reclaiming memory from existing jobs. Each SSAS command (query, processing,
backup, synchronization, and so on) is associated with jobs that run on threads and
use system resources. We can lower the value of this setting to run more jobs in par-
allel (though the performance of each job could suffer). Two properties control the
maximum amount of memory that a SSAS instance could use. Once memory us-
age reaches the value specified by <Memory><TotalMemoryLimit> , the cleaner
thread becomes particularly aggressive at reclaiming memory.
The <Memory><HardMemoryLimit> property specifies the absolute memory lim-
it—SSAS will not use memory above this limit. These properties are useful if you
have SSAS and other applications installed on the same server computer. You
should reserve some memory for other applications and the operating system as
well. When HardMemoryLimit is reached, SSAS will disconnect the active ses-
sions, advising that the operation was cancelled due to memory pressure.
Note
All memory settings are expressed in percentages if the values are less than or
equal to 100. Values above 100 are interpreted as kilobytes. All memory config-
uration changes require restart of the SSAS service to take effect.
In the prior releases of Analysis Services, you could only specify the minimum and
maximum number of threads used for queries and processing jobs. With SSAS
2012, you can also specify the limits for the input/output job threads using the
<ThreadPool><IOProcess> properties.
The <Process><IndexBuildThreshold> property governs the minimum num-
ber of rows within a partition for which SSAS will build indexes. The default value is
4096 . SSAS decides which partitions it needs to scan for each query based on the
partition index files. If the partition does not have indexes, it will be scanned for all
the queries. Normally, SSAS can read small partitions without greatly affecting query
performance. But if you have many small partitions, you should lower the threshold
to ensure each partition has indexes.