November 6-9, Seattle, WA

Secrets of SSAS Storage

Stacia Misner

Principal Consultant

Data Inspirations

Stacia Misner Consultant, Educator, Mentor, Author

SQL Server MVP, SSAS Maestro

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Overview

Storage Architecture

Partitions

Aggregations

Storage Impact on Queries

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Storage Architecture

Query Architecture

Dimension Storage

Measure Group Storage

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Query Architecture

Analysis Services Server

Client Application MDX Query

Storage Engine

Formula Engine

Formula Engine Cache

Calculation Engine Subcube Operations

Dimension Data

Measure Group Data

Storage Engine

Storage Engine Cache Attribute Store

Hierarchy Store

Aggregations

Fact Data

Compute Cell Data

Populate Axes

Query Parser

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Dimension Storage

Attribute Store

Key Store

DataID Attribute Key Member

Property Store

DataID Attribute Property

Ordered by DataID for fast random access

Key Hash Name Hash

Relationship Store

DataIDs

Bitmap Indexes

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Dimension Storage

Hierarchy Store

Set Store

DataID

Structure Store (Parent level)

Level Index

DataID Parent

DataID

FirstChild

DataID

Children

Count

Path of each member

Applies only to natural hierarchies

Structure Store (Child level)

Level Index

DataID Parent

DataID

FirstChild

DataID

Children

Count

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Measure Group Storage

STORAGE ENGINE CACHE Loads as queries execute

Clears with cleaner thread or processing of

partition

AGGREGATION DATA Responds to request with aggregated values

in storage

Summarizes lower level aggregated values

on-the-fly as needed

FACT DATA Scans MOLAP partitions and partitions

segments in parallel

Uses bitmap indexes to scan pages to find

requested data

Storage Engine

Measure Group Data

Storage Engine

Storage Engine Cache Aggregations

Fact Data

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Partitions

Partitioning Strategy

Partition Storage

Partition Design

Merging Partitions

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Partitioning Strategy

Storage

MOLAP

HOLAP

ROLAP

Query

20% Agg

30% Agg

15% Agg

Processing

Current Year

Prior Year

History

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MOLAP

cache

Data

Partition Storage: MOLAP

Multidimensional OLAP

Storage of data and aggregations in cache

Highly compressed and indexed

RDBMS UDM

Analysis Server

MDX

Aggs

Unified Dimensional Model

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MOLAP

cache

SQL

Partition Storage: HOLAP

Hybrid OLAP

Storage of aggregations only in cache

Translation of MDX to SQL for retrieval of detail data

RDBMS UDM

Analysis Server

MDX

Data MDX

Aggs

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SQL

Partition Storage: ROLAP

Relational OLAP

Relational storage of data and aggregations

Real-time analysis

RDBMS UDM

Analysis Server

Data/Aggs MDX

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ROLAP Dimension

Dimension data exists in relational storage only

Analysis Services maintains a cache of requested dimension data

Use case: Hundreds of millions of members in dimension

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Partition Design

Use one source fact table per partition

Insulate partition from table changes by using a view

Table Binding

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Partition Design

Use separate queries to same fact table for each partition

Configure as last step in cube design to use most recent DSV

Query Binding

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2005

Merging Partitions

Use Management Studio interface for manual merge

Execute XMLA script for automated merge in Execute DDL Task (SSIS)

2008

2007

2006 History

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Aggregations

Aggregation Concepts

Aggregation Usage

Aggregation Wizard Optimizations

Aggregation Designer

Usage Based Optimization

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Aggregation Concepts

Aggregation-aware queries Sales by country, gender, or both Sales by category Sales by year Sales by group

Aggregation-less queries Sales by gender and year Sales by category and year Sales by country and category

Aggregation design

Indexed view for aggregation (ROLAP only)

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Aggregation Concepts

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Aggregation Usage

Default

Full

Include in every aggregation (or a lower level attribute)

Use only for most commonly used attributes, sparingly

None

Exclude in every aggregation

Use for infrequently used attributes

Unrestricted

No constraints

Analysis Services decides whether to include or exclude

Rule of thumbuse only 5-10 Unrestricted attributes per dimension

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Aggregation Usage Default Rules

ATTRIBUTE

FULL NONE UNRESTRICTED

Granularity attribute for measure group

Special dimension types*

Natural hierarchies

with attribute relationships

Non-aggregatable attributes

All others

*Many-to-many dimension

Unmaterialized referenced dimension

Data mining dimension

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Aggregation Wizard Optimizations

Remove unneeded attributes

Add user hierarchies for natural

hierarchies where possible

Ensure correct attribute relationships

Set AttributeHierarchyEnabled to False

for member properties

Configure AggregationUsage in

advance

Use correct estimates for partition

rows and attributes within a partition

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Aggregation Designer

Profiler: Aggregation hit

Profiler: No aggregation hit

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Usage Based Optimization

SERVER PROPERTY

SETTING

Log\QueryLog\CreateQueryLogTable true

Log\QueryLog\QueryLogConnectionString Data source=localhost;Initial Catalog=DW

Log\QueryLog\QueryLogSampling 1

Log\QueryLog\QueryLogTableName OlapQueryLog

AS creates if doesnt exist, else logs to table

Clear property value to disable

logging

OlapQueryLog records deleted when:

Measures added to or removed from measure group Dimensions added to or removed from measure group Attributes added to or removed from dimension

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Usage Based Optimization OLAPQueryLog

Filter Criteria Query Details

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Storage Impact on Queries

Which Engine is the Bottleneck?

Query Analysis

Partitioning

Aggregation Design

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Which Engine is the Bottleneck?

Time to execute query (cold cache)

Storage Engine time = add elapsed time for each Query Subcube

event

Formula Engine = Total execution time (Query End event) Storage Engine time

Bottleneck is engine consuming 30% or more of total query execution

time

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Prepare for Query

Clear Cache

Reload MDX Script (without caching)

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Profiler Results Begin

Query Begin indicates successful query parsing

Serialize Results Current counts members on each axis

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Storage Engine Reads Partitions

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Query Subcube Event

Sum each Query Subcube Event to compute total Storage Engine

query time

Review TextData for vectors returned to formula enginevery cryptic

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Query Subcube Verbose Event

Use Query Subcube Verbose Event to understand vectors

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Subcube Details

VALUE RESULT

0 Default member returned

* All members returned

+ Selected members returned

- Slice below granularity returned

4 Single members DataID

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Profiler Results End

Serialize Results Current reports total number of cells in query results

Query End reports total query duration

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Duration Analysis

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Partitioning

Create multiple partitions to enable optimal scans of fact data

Partition by one or more attributes used in many queries, such as Year

Define slice

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Aggregation Design

Aggregation Design Wizard

View aggregation candidates

Update member and fact record counts

Develop and apply aggregation design

Usage-Based Optimization Wizard

Capture query sampling in usage log

Tune aggregation performance to actual usage

Aggregation Utility (2005) / Aggregation Designer (2008)

Override aggregation design algorithm

Best Practice!

Good Practice

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Resources

Analysis Services 2008 Performance Guide

http://tinyurl.com/9vqqmuy

Analysis Services 2008 R2 Operations Guide

http://tinyurl.com/8wvdyg4

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Stacia Misner

smisner@datainspirations.com

blog.datainspirations.com

Twitter: @StaciaMisner

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November 6-9, Seattle, WA

Thank you for attending this session and

the 2012 PASS Summit in Seattle

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