Adam Jorgensen
Pragmatic Works
Performance Optimization in
SQL Server Analysis Services 2008
Agenda
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SSAS Query Processing Architecture
Enhancing Query Performance
Improving Processing Performance
Tuning Server Resources
Query Processing Architecture
Client Application MDX
Query
• Session
Management
• Query
Processing
• Data Retrieval
Session Management
XML/A Listener
Session Manager
Security Manager
Query Processor
Query Processor
Cache
Storage Engine
Storage Engine
Cache
Query Processing
Data Retrieval
Dimension Data
Measure Group Data
Attribute Store
Fact Data
Hierarchy Store
Aggregations
Job Architecture
Request
• CoordinatorExecutionMode
• Negative means max
number of jobs per core
• Zero means no limit
• Positive means number of
jobs per server
• Default is -4
• Works in tandem with
MAXTHREADS and
MAXPARALLEL
Thread
Coordinator Job
…
Job 1
Thread
Job 2
Job N
Thread
Thread
Query Processor
• Executes MDX Queries and returns cell and
row sets.
• Builds an execution Plan to translate request
into one or more SubCube requests.
• Uses the Query Processor Cache to store the
results for reusability
Query Processor Cache
• 3 Contexts
• Cache Rules
– Calculations created at query time
– Context is chose by scope
– Try for maximum re-use in the
Global Cache
• Partial Expressions are not
Cached
Query Context
Session Context
Global Context
Data Retrieval
Coordinator Job
First Segment Job
Second Segment Job
Thread
Thread
Creates SubCube Request
Storage Engine
Cache (Y/N)
…
Last Segment Job
Thread
Aggregation
(Y/N)
Fact
Table/Partition
Agenda
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SSAS Query Processing Architecture
Enhancing Query Performance
Improving Processing Performance
Tuning Server Resources
Enhancing Query Performance
Base lining
Query Speed
Cache
Warming
Diagnosing
The Problem
Optimizing
MDX
Optimizing
Dimensions
Using
Partitions
Maximizing
Aggregations
Usage Based
Optimization
Base Lining Query Speed
• Trace Info
– 0 – attribute is not included in query
– * - ever member was requested
– + - two or more members were requested
– <integer value> - a single member of the
attribute was hit
Clear
Cache
Trace
Query
Warm
Cache
Trace
Again
Compare
Diagnosing the Problem
• Storage Engine
– Long running
sub-cube events
• Optimize
dimension
design
• Design
aggregations
• Use partitions
• Query Processor
• See delay in other
steps (query
processing)
• Optimize MDX
• Look for
redundant
queries
Demo
• Using SSAS and Profiler
• Get the query Excel is running
Identify Attribute Relationships
• Default relations to Key
• Base for Indexes
• Cross products don’t need to go
through key
• Aggregations built on attributes can be
used for related attributes
• Flexible vs. Rigid
Implementing Effective User Hierarchies
• Attribute vs. User
Hierarchies
– Aggregation Usage
Property
• Natural vs. Unnatural
Hierarchies
Demo
• Attribute Relationships and Hierachies
Using Partitions
• Advantages
– Partition Slicing
– Aggregation Design
• Tips for Using Partitions
– Slide Aggregations along
partition hierarchy
• i.e. – Last 7 days, Last 30
Days, 90, 6 months, etc..
– Indexes or slices will not
be defines for partitions
with fewer rows (4096
default)
• Sizing
• Increasing processing
speed and flexibility
• Increase manageability
of bringing in new data
• Support multiple
aggregation designs
Demo
• Implementing Partitions
Maximizing Aggregation Value
Building,
Suggesting,
Influencing
Aggregations
Interpreting
Aggregations
Detecting Aggregation
Hits
Demo
• Aggregations and Usage Based Optimization
Agenda
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•
•
•
SSAS Query Processing Architecture
Enhancing Query Performance
Improving Processing Performance
Tuning Server Resources
Processing Job Overview
• Parent – Child Jobs
• Best Opportunity to Increase Performance and
Scale
Measure
Group
Partition
Fact Table &
Aggregations
Parent
Processing Job
Parent
Partition/ Child
Processing
Child Fact Data
Child
Aggregation
Parent
Partition/ Child
Processing
Child Fact Data
Where Are You Spending Your Time?
• Partition or Dimension Processing ?
• ProcessFull vs. ProcessData and ProcessIndex
• During ProcessData
– MSOLAP:Processing – Rows read/Sec >0
• During ProcessIndex
– MSOLAP:Proc Aggregations – Row created/Sec > 0
Dimension Processing Best Practices
• Use SQL Views to Implement Query Binding
• Optimize Attribute Processing Across Multiple
Sources
• Reduce Unnecessary Attributes
• Adjust/Remove Bitmap Indexes
• Tune Relational Processing Query
Partition Processing Architecture
• Processes Using Jobs
• Three Concurrent Threads
– Send SQL to extract source
data
– LookUp Dimension Keys and
populate processing buffer
– Write Buffer to disk when it
fills
• Aggregations and Bitmap
Indexes
– May also overflow to disk –
created in memory during
processing
Process Fact
Data
Build
Aggregations
Build Bitmap
Indexes
Partition Processing Best Practices
• Inserts
– ProcessFull vs. ProcessAdd
– Rotating Partitions
• Updates
– ProcessFull
– Journaling to only implement Inserts
• (See Insert Techniques)
• Deletes
– Partitioning
– ProcessUpdate
– Remove Data From Table and ProcessFull (longer)
• Pick Efficient Data Types
Tuning the Relational Query
• Minimal Joins in Source Queries
• Partitioning Alignment
– Each SSAS partition should only hit 1 Relational Partition
– More than 1 cube partition can hit 1 relational partition
• Clustered Indexes
– Especially without 1:1 partition relationship
• Keep FillFactor VERY high
• Data Compression – Reduce IO
• Reduce Locking when possible
Tuning ProcessIndex Phase
• Avoid Spilling Data to Disk
Partition
Process Job
– MSOLAP:Proc
Aggregations\Temp file
bytes written/sec
• Eliminate IO bottleneck
• Increase Partitions for
Parallelism
Segments
Segments
Segments
Thread n
Thread 1
– Increase means faster
aggregation processing
Thread 0
• MSOLAP:Proc Aggregations
– Row created/sec
n = CoordinatorBuilMaxThread
Agenda
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•
•
•
SSAS Query Processing Architecture
Enhancing Query Performance
Improving Processing Performance
Tuning Server Resources
Tuning Server Resources
• PreAllocate Physical Ram for SSAS
– Hard reservation – otherwise memory will be
released when not under load
• Using Large Pages
– Lock Pages in Memory
– Cannot be swapped to page file
• Need to watch Carefully
• Leave 20% for the OS
• Disable Flight Recorder
Questions and Where to Find Adam