Monitoring Cube Performance and Usage - Expert Cube Development with SSAS Multidimensional Models - page 322

Another reason for paging physical memory to disk is the System
File Cache. By default, Windows uses the available unused physical
memory as System File Cache. This would not be an issue if the
concept of "unused" was really of memory not used by anyone. If
applications or file sharing result in a lot of sustained cached read
I/O, the operating system gives physical RAM to the file cache and
paginates the memory of idle processes if necessary. In other words,
if we were working on a 16 GB RAM server and we copied a 20 GB
file containing a backup file to an external disk, we could paginate all
the memory used by Analysis Services if it was not in use during the
copy. To avoid this kind of situation, we could reduce the size of the
paging file (if virtual memory cannot be paginated to disk, it has to be
kept in physical RAM) or use the SetCache utility that is discussed at
http://tinyurl.com/SetCache .
The memory requested by a process is always requested as virtual memory. In
situations where the virtual memory allocated by Analysis Services is much larger
than the available physical RAM, some Analysis Services data will be paged to
disk. As we said, this could happen during cube processing. We should avoid these
situations by configuring Analysis Services' memory settings (more on this we
discuss later), so that they limit the amount of memory that can be allocated by it.
However, when no other processes are asking for memory, we might find that by
having limited Analysis Services' memory usage in this way, we are preventing it
from using extra memory when it needs it, even when that memory is not used by
anything else.
Later in this chapter, we will explore the available memory options for Analysis
Services and see how to monitor its memory usage.
I/O Operations
Analysis Services generates I/O operations both directly and indirectly. A direct
I/O request from Analysis Services is made when it needs to read data from or
write data to disk; and when it sends query results back to the client, which involves
an inter-process communication, typically made through network I/O operations.
The indirect I/O requests generated by Analysis Services come from paging disk
operations, and it is very important to be aware that they can happen, because
they cannot be seen using the performance counters we might typically monitor
for Analysis Services. Paging operations are not visible to the Analysis Services
process and can be seen only by using the appropriate operating system performance
counters, such as Memory: Pages / sec .