Oracle Exadata X2-8: A Critical Review

Oracle Exadata X2-8: A Critical Review
Mike Ault
Oracle Guru
Texas Memory Systems

Michael R. Ault
Oracle Guru
Nuclear Navy 6 years
Nuclear Chemist/Programmer 10 years
Kennedy Western University Graduate
Bachelors Degree Computer Science
Certified in all Oracle Versions Since 6
Oracle DBA, author, since 1990
Oracle Ace

Books by Michael R. Ault

Statspackanalyzer.com
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Looks for IO bottlenecks and other configuration issues.
Straightforward tuning advice

What Is Exadata X2-8?
Is it software?
Is it hardware?
Is it the Borg?

Exadata as Borg?

Not Really (at least not yet…)
Exadata is a combination of hardware and software
Exadata takes state of the art disk, computer and flash technology and combines it with specially designed software from Oracle.
Exadata hardware can only run Oracle software

Exadata X2-8 Hardware
(Looks to be the SUN X4800)

Traditional Setup

Exadata Setup
Each Exadata Cell has 4-96 GB flash cards

Exadata X2-8 Storage Hardware
Sun x4270 M2 servers that contain dual six-core Xeon L5640 processors running at 2.26 GHz, with 24GB of memory
4-96 MB flash cards for Smart flash cache used to accelerate disk reads
Disks are either high performance low capacity 15K or low performance high capacity 7.5K
Lose 66% or more of raw space for redundancy options or formatting losses
High Perf: 7.2 down to 2 TB per cell
Low Perf: 24 down to 7 TB per cell
You pay license on a per disk basis
$10,000.00/disk, $120,000.00 per cell
Get IOPS based on large number of disks (168 to get 50K IOPS)
200 IOPS/DISK*168 DISK=33,600 IOPS so this is doubtful
Promises of 1,000,000 IOPS from FLASH (read-only)
Full X2-8 hardware cost: $1,500,000.00 (doesn’t include software!)
All prices/data taken from:
Oracle Exadata and Exalogic Pricelist, July 1, 2011
Oracle Technology Global Pricelist, July 1, 2011, Software Investment Guide
Exadata Smart Flash Cache and the Sun Oracle Database Machine, Oracle, Oct 2009

Exadata X2-8 Specific Software

Something to Note:

Exadata X2-8 Oracle Software
License is per CPU
Approximately $51,500.00 per CPU for all Oracle software
128 CPU * $51,500.00 = $6,592,000.00
Add the Cell license cost of $1,680,000.00
Total license cost: $8,272,000.00
Total Hardware cost: $1,500,000.00
Total cost (plus shipping, handling and installation, support): $9,772,000.00
All prices taken from:
Oracle Exadata and Exalogic Pricelist, July 1, 2011
Oracle Technology Global Pricelist, July 1, 2011, Software Investment Guide

Exadata Specific Software Features:Smartscan
Goal reduce the data volume into the SGA as will only match the result set
Less load on IB and RAC interconnects+CPU
Predicate Filtering processes WHERE in storage
Column Projections only returns columns = sql
Bloom filter Joins passes matching values to storage cells to match only requested values
Storage Indexes High/Low Values @1MB disk
Data Mining Scoring functions run on storage

Smartscan
First: Traditional Processing (non-indexed select):
The client issues a SELECT statement with a predicate to filter and return only rows of interest.
The database kernel maps this request to the file and extents containing the table being scanned.
The database kernel issues the I/O to read the blocks.
All the blocks of the table being queried are read into memory. Then SQL processing is done against the raw blocks searching for the rows that satisfy the predicate.
Lastly the rows are returned to the client.
From: Oracle, A Technical Overview of the Oracle Exadata Database Machine and Exadata Storage Server, April 2011

Smartscan
Smartscan:
The client issues a SELECT statement with a predicate to filter and return only rows of interest.
The database kernel determines that Exadata storage is available and constructs an iDB command representing the SQL command issued and sends it the Exadata storage.
The CELLSRV component of the Exadata software scans the data blocks to identify those rows and columns that satisfy the SQL issued.
Only the rows satisfying the predicate and the requested columns are read into memory.
The database kernel consolidates the result sets from across the Exadata cells.
Lastly, the rows are returned to the client.
From: Oracle, A Technical Overview of the Oracle Exadata Database Machine and Exadata Storage Server, April 2011

SO…
Smartscan is good for full table scan issues where no indexes are available
Have heard that Oracle suggests removing indexes, but how does smartscan resolve FK-PK issues?
In complex OLTP or DSS/DWH queries smartscan may not help
Depends on min/max storage indexes which can have issues with changing data
May not be efficient on partitioned tables when a partitioned-wise join can’t be used
In frequently updated tables smartscan may be bypassed, or, blocks will be passed that are inconsistent, requiring the DB server to filter them and retrieve the proper block from the undo segments
From:
Oracle: A Technical Overview of the Oracle Exadata Database Machine and Exadata Storage Server, April 2011
Teradata: Exadata is Still Oracle, March 2011

Exadata Specific Software Features:Smart Flash Cache
Seems to be lots of confusion between Flash cache in the server and flash cache at the DB level
Flash cache is turned on at the server in Oracle Linux and Sun using initialization parameters
Smart flash cache is automatic with the Exadata cell and requires no operator intervention

Exadata Smart Flash Cache
Each cell comes with 384 GB of Exadata Smart Flash Cache.
In the Database Machine X2-8 and Full Rack X2-2 there is 5.3 TB of Flash
Provides a 10x improvement in response time for reads and 100x improvement in IOPS for reads over regular disk
Delivers a 10x blended performance average of read and write operations.
Doesn’t use Least Recently Used (LRU) algorithm
The Storage Server Software keeps track of data access patterns and caches to avoid polluting the cache.
Managed automatically and does not allow manual tuning.
Specific objects key to performance can be pinned in cache.
Only for EXADATA
From: An Oracle White Paper, October 2009,Exadata Smart Flash Cache and the Sun Oracle Database Machine

Database Flash Cache
A victim cache, it stores clean (unmodified) blocks that have been evicted from the SGA buffer cache
If a block has been modified, it is first written to disk, then it is written to the Database Smart Flash Cache.
Blocks can later be returned to the SGA as required.
If a block cannot be found in the SGA buffer cache or the Database Smart Flash Cache, it is retrieved from disk.
This is only done when DBWR has time to perform the operations
Only works (in supported mode) on Oracle Linux and Oracle Sun Solaris
Set up with two-initialization parameters:
DB_FLASH_CACHE_FILE
DB_FLASH_CACHE_SIZE
FROM: An Oracle White Paper, September 2010, Oracle Database Smart Flash Cache

SO…
Exadata flash cache can benefit both OLTP and DSS/DWH
Only for non-changing, frequently accessed data
Most helpful for reads
Is basically a write-through cache using access statistics to optimize storage of hot blocks
On external flash so not as fast as database flash cache

IORM(IO Resource manager)
DBRM has been enhanced for use with Exadata.
DBRM lets the user define and manage intra and inter-database I/O bandwidth.
Consumer groups are allocated a percent of the available I/O bandwidth and the DBRM ensures these targets are delivered.
The database tags I/O with the database and consumer group.
The intra-database I/O allocations are defined and managed at the database
The inter-database I/O allocations are defined within the software in the Exadata cell and managed by the I/O Resource Manager (IORM).
The Exadata cell software ensures that inter-database I/O resources are managed and properly allocated within, and between, databases.
Overall, DBRM ensures each database receives its specified amount of I/O resources and user defined SLAs are met.
Note that IORM currently provides no management of objects cached in Flash
FROM:
An Oracle White Paper, April 2011, A Technical Overview of the Oracle Exadata Database Machine and
Exadata Storage Server
Mixed Consolidated Workloads and the Sun Oracle Database Machine By Robert Stackowiak February 6, 2010

IORM
DBRM are created at the Database
IORM are created at the CELL
Creating IORM Plans on Oracle Exadata:
Create a simple plan:CellCLI> alter iormplan dbplan=((name=db1_prod, level=1, allocation=70),(name=db2_prod, level=1, allocation=30),(name=db1_dev, level=2, allocation=100),(name=db1_test, level=3, allocation=70),(name=other, level=3, allocation=40)),catplan=''CellCLI> alter iormplan active
From: http://pauloferreiraportugal.blogspot.com/2011/04/creating-iorm-plans-on-oracle-exadata.html

Other IO Features
Utilizes creation of cell disks from whole physical disks
Cell disks are then split into ASM DISKS with HOT and COLD ASM DISKS
The Hot ASM DISKS (outer edge) are grouped together and used for hot data
The Cold ASM DISKS are grouped together and used for cold data

SO…
IORM is only for Exadata at the Cell level
IORM doesn’t regulate or understand flash cache operations
Can be used in concert with DBRM to control resources

Exadata Specific Software Features:Storage Indexes
The Storage Server Software creates and maintains the Storage Index
Tracks min and max values of columns for tables stored on that cell.
When a query specifies a WHERE clause, but before any I/O, the Exadata software uses the Storage Index to determine if rows with the specified column value exist in the cell
Many SQL Operations will run dramatically faster because large numbers of I/O operations are automatically replaced by a few lookups.
Storage Indexes are created and maintained by the Exadata Storage Server Software.
Indexes must be rebuilt every shutdown/startup operation
Can cause false positives, but not false negatives

Exadata Specific Software Features:Hybrid Columnar Compression
Combination of both row and columnar methods for storing data.
Achieves the compression benefits of columnar storage, avoiding the performance issues of a pure columnar format.
A logical construct called the compression unit is used to store a set of Exadata Hybrid Columnar-compressed rows.
When data is loaded, column values are detached from the set of rows, ordered and grouped together and then compressed.
After the column data for a set of rows has been compressed, it is fit into the compression unit.
Not good for volatile data
From: An Oracle White Paper: December 2009, Exadata Hybrid Columnar Compression

Exadata Specific Software Features:Hybrid Columnar Compression
Data must be loaded using data warehouse bulk loading techniques.
Exadata HCC tables can still be modified using conventional Data Manipulation Language (DML) operations, such as INSERT and UPDATE.
Examples of bulk load operations commonly used in data warehouse environments are:
Insert statements with the APPEND hint
Parallel DML
Direct Path SQL*LDR
Create Table as Select (CTAS)

Exadata Specific Software Features:HCC Warehouse Compression
Warehouse Compression Syntax
CREATE TABLE emp (
emp_id NUMBER
, first_name VARCHAR2(128)
, last_name VARCHAR2(128)
) COMPRESS FOR QUERY [ LOW | HIGH ];
Low gives 6X
High gives 10X

Exadata Specific Software Features:HCC Archive Compression
Online Archival Compression Syntax
CREATE TABLE emp (
emp_id NUMBER
, first_name VARCHAR2(128)
, last_name VARCHAR2(128)
) COMPRESS FOR ARCHIVE [ LOW | HIGH ];
Gives up to 15X
For infrequently accessed data
Will cause notable decrease in performance

SO…
HCC good for infrequently accessed data
Use OLTP compression for OLTP only 4X
Have seen reports that the needed decompression/recompression due to changing data can be quite expensive performance wise
Must do initial load with pre-built blocks

Data Mining in Oracle Exadata
Scoring is the process of applying a data mining model to data to generate predictions.
Scoring processes require significant system resources.
Vast amounts of data may be involved, and algorithmic processing may be very complex.
With Oracle Data Mining, scoring can be off-loaded to intelligent Oracle Exadata Storage Servers

Overall
From: Teradata, Exadata is Still Oracle, March 2011

Overall
Low
Simple star schemas
Simple joins
Fixed data
High
Hybrid or snowflake schemas
Complex joins, summaries, etc.
Changing data

Exadata Strengths
One vendor
High bandwidth data path
Moves processing (in some cases) closer to the data
Offers advanced compression for archival/fixed data
Offers 5-20X acceleration for simple queries against relatively calm data
Within the Exadata X2-2 family, easy upgrades

Exadata Weaknesses
Limited to one vendor for hardware and software (limited flexibility)
Not good for rapidly changing data
Expensive
Complex hardware and software
Daisy cutter approach to upgrade from existing system
Heavy metal approach to performance
For DP if you go Dataguard, must use Exadata

Summary
For a new shop or project with no existing hardware Exadata is a good option if you can afford it
For consolidation Exadata may be a good fit
If you intend on keeping your licenses where they are and just getting an Exadata, it is really expensive
Uses “old” technology (disks)
May have issues with rapidly changing data (frequent IUD) negating the new performance features
Can get similar or better performance improvements without getting rid of existing technologies.

Comparison of Exadata X2-8 to A RamSan710 Based Database System

Main Storage-RamSan710
1-U 1-5TB SLC Flash
400,000 IOPS
5 GB/s bandwidth
4 QDR Infiniband ports
175 microsecond latency worst case (4k)
Base cost 5TB - $150,000.00
12 - $1,800,000.00 (Raid 0) 30 TB

How About Some CPUs?
2-SUN Fire X4800 (Same as Exadata)
Each with:
8-8 core 2.26 GHz 7560 CPUs
1 TB memory
8 PCIe modules
Cost: $268,392.00

Some Licenses(Same base Oracle licenses as Exadata)
128 CPUS*$51,500.00=$6,592,000
No need for Cell licenses since no Cells!

Misc(Support and connection)
Switches
Rack
Cables, etc
$40,000.00

Some Database Flash cache
6 – RamSan-70 Gorillas
5.4 TB total of database Flash cache (2.7 TB per server)
600,000 IOPS/card
70 Microsecond read latency
$134,400.00

Total
RamSan710s $1,800,000.00
Servers $268,392.00
Oracle $6,592,000.00
RamSan70s$134,400.00
Misc $40,000.00
Total $8,834,792.00
(Plus shipping, handling, installation, support)
Of course this is street price, once discounts for bulk purchases and other things are removed, probably closer to 6-7 million.

A Million here, a Million There
So, what are you getting for a million less?
5 GB/s*6=30 GB/s bandwidth
30 TB usable raided flash with 175 microsecond latency for all transactions
400,000*6=2,400,000 IOPS from Storage
2,400,000 IOPS from Cache
128 CPUS and 2 TB of memory
Database Independence
OS independence
Less complexity
Better Performance
Lower operating costs (lower license, electric and cooling)
Great performance on OLTP/DWH/DSS

All-In-One-Place
*Note: Various sources quote the Exadata X2-8 HP capacity from 28-45 usable TB. Adding 15 TB RS710 RAIDed Flash: $900,000.00

Summary
Exadata uses old technology (disk), write through flash caches and new software to brute force performance
New technology such as Flash and SSD as storage can get the same benefits, cheaper
Exadata locks you into Oracle technology and hardware
Using newer technology keeps your options open with better performance

Questions/Comments?

Thank You!
Mike Ault
oracle@ramsan.com
http://www.statspackanalyzer.com/

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Oracle Exadata X2-8: A Critical Review

by Texas Memory Systems, and IBM Company on Jul 28, 2011

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