adam jorgensen pragmatic works performance optimization in sql server analysis services 2008
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Adam JorgensenPragmatic Works
Performance Optimization in SQL Server Analysis Services 2008
Agenda
• SSAS Query Processing Architecture• Enhancing Query Performance• Improving Processing Performance• Tuning Server Resources
Query Processing Architecture
• Session Management
• Query Processing
• Data Retrieval
Session Management
XML/A Listener
Session Manager Security Manager
Query Processing
Query Processor Query Processor Cache
Data Retrieval
Storage Engine Storage Engine Cache
Dimension Data
Attribute Store
Hierarchy Store
Measure Group Data
Fact Data
Aggregations
Client Application MDX Query
Job Architecture
Coordinator Job
Job 1
Thread
Request
Job 2
Thread
Job N
Thread
…
Thread
• 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 andMAXPARALLEL
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 Global Context
Session Context
Query Context
Data Retrieval
Coordinator Job
First Segment Job
Thread
Second Segment Job
Thread
Last Segment Job
Thread
…
Creates Sub-Cube Request
Storage Engine Cache (Y/N)
Aggregation (Y/N)
Fact Table/Partition
Agenda
• SSAS Query Processing Architecture• Enhancing Query Performance• Improving Processing Performance• Tuning Server Resources
Enhancing Query Performance
Base lining Query Speed
Diagnosing The Problem
Optimizing Dimensions
Maximizing Aggregations
Usage Based Optimization
Using Partitions
Optimizing MDX
Cache Warming
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
Vs.
• 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
Original
Optimized
• 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
Detecting Aggregation Hits
Interpreting Aggregations
Building, Suggesting, Influencing
Aggregations
Demo
• Aggregations and Usage Based Optimization
Agenda
• 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
Fact Table & Aggregations
Partition
Measure Group
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– MSOLAP:Proc
Aggregations\Temp file bytes written/sec
• MSOLAP:Proc Aggregations – Row created/sec– Increase means faster
aggregation processing• Eliminate IO bottleneck• Increase Partitions for
Parallelism
SegmentsSegments
Segments
PartitionProcess Job
Thre
ad 0
Thre
ad 1
Thre
ad n
n = CoordinatorBuilMaxThread
Agenda
• 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
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