Question

I am fairly new to SSAS and SQL Server but Google didn’t help. I am grateful for pointers to the right documentation.

I have setup a cube and I query it from Excel using pivot tables.

The very first update/request I run takes around 10 secs to run, however the following request complete in less then a second.

When I wait a while without querying (10 minutes or so) the first update takes 10 seconds again.

How can I prevent this behavior and speed up the first update?

I imagine, that SQL Server unloads the cube from RAM after a while. Is there a way to mark the cube as “keep in RAM”.

Thanks,

Cilvic

Answer 1

The most likely reason that it gets removed from cache is SQL Server memory pressure. How much RAM does the server have?

If adding more memory is not an option, you could perhaps schedule a periodic (hourly say) cache warm-up: How to warm up the Analysis Services data cache using Create Cache statement?:

For example, ascmd.exe could be used
every hour to execute all queries in a
directory keeping the cache ready for
subsequent user queries. The other
approach, which has been used, is to
create a cache query for each user
query. This is feasible if the MDX
query is part of a report, then one
simply adds another query that has the
side effect of populating the cache,
thereby speeding up the next query.

Also: Build Your Own Analysis Services Cache-Warmer in Integration Services

There are several SSAS performance counters you can monitor:

• MSAS 2008:Memory Cleaner Current
  Price Current price of memory,
  $/byte/time, normalized to 1000.

• MSAS 2008:Memory Cleaner Balance/sec
  Rate of balance+shrink operations.

• MSAS 2008:Memory Cleaner Memory
  shrunk KB/sec Rate of shrinking, in
  KB/sec.

• MSAS 2008:Memory Cleaner Memory
  shrinkable KB Amount of memory, in
  KB, subject to purging by the
  background cleaner.

• MSAS 2008:Memory Cleaner Memory
  nonshrinkable KB Amount of memory, in
  KB, not subject to purging by the
  background cleaner.

• MSAS 2008:Memory Cleaner Memory KB
  Amount of memory, in KB, known to the
  background cleaner. (Cleaner memory
  shrinkable + Cleaner memory
  nonshrinkable.)