Archive for the 'Exadata Database Machine X2-8 HP Full Rack' Category

Exadata Database Machine X2-2 or X2-8? Sure! Why Not? Part II.

In my recent post entitled Exadata Database Machine X2-2 or X2-8? Sure! Why Not? Part I, I started to address the many questions folks are sending my way about what factors to consider when choosing between Exadata Database Machine X2-8 versus Exadata Database Machine X2-2. This post continues that thread.

As my friend Greg Rahn points out in his recent post about Exadata, the latest Exadata Storage Server is based on Intel Xeon 5600 (Westmere EP) processors. The Exadata Storage Server is the same whether the database grid is X2-2 or X2-8. The X2-2 database hosts are also based on Intel Xeon 5600. On the other hand, the X2-8 database hosts are based on Intel Xeon 7500 (Nehalem EX). This is a relevant distinction when thinking about database encryption.

Transparent Database Encryption

In his recent post, Greg brings up the topic of Oracle Database Transparent Data Encryption (TDE). As Greg points out, the new Exadata Storage Server software is able to leverage Intel Advanced Encryption Standard New Instructions (Intel AES-NI) found in the Intel Integrated Performance Primitives (Intel IPP) library because the processors in the storage servers are Intel Xeon 5600 (Westmere EP). Think of this as “hardware-assist.” However, in the case of the database hosts in the X2-8, there is no hardware-assist for TDE as Nehalem EX does not offer support for the necessary instructions. Westmere EX will—someday. So what does this mean?

TDE and Compression? Unlikely Cousins?

At first glance one would think there is nothing in common between TDE and compression. However, in an Exadata environment there is storage offload processing and for that reason roles are important to understand. That is, understanding what gets done is sometimes not as important as who is doing what.

When I speak to people about Exadata I tend to draw the mental picture of an “upper” and “lower” half. While the count of servers in each grid is not split 50/50 by any means, thinking about Exadata in this manner makes understanding certain features a lot simpler. Allow me to explain.

Compression

In the case of compressing data, all work is done by the upper half (the database grid). On the other hand, decompression effort takes place in either the upper or lower half depending on certain criteria.

  • Upper Half Compression. Always.
  • Lower Half Compression. Never
  • Lower Half Decompression. Data compressed with Hybrid Columnar Compression (HCC) is decompressed in the Exadata Storage Servers when accessed via Smart Scan. Visit my post about what triggers a Smart Scan for more information.
  • Upper Half Decompression. With all compression types, other than HCC, decompression effort takes place in the upper half. When accessed without Smart Scan, HCC data is also decompressed in the upper half.

Encryption

In the case of encryption, the upper/lower half breakout is as follows:

  • Upper Half Encryption. Always. Data is always encrypted by code executing in the database grid. If the processors are Intel Xeon 5600 (Westmere EP), as is the case with X2-2, there is hardware assist via the IPP library. The X2-8 is built on Nehalem EX and therefore does not offer hardware-assist encryption.
  • Lower Half Encryption. Never.
  • Lower Half Decryption. Smart Scan only. If data is not being accessed via Smart Scan the blocks are returned to the database host and buffered in the SGA (see the Seven Fundamentals). Both the X2-2 and X2-8 are attached to Westmere EP-based storage servers. To that end, both of these configurations benefit from hardware-assist decryption via the IPP libarary. I reiterate, however, that this hardware-assist lower-half decryption only occurs during Smart Scan.
  • Upper Half Decryption. Always in the case of data accessed without Smart Scan. In the case of X2-2, this upper-half decryption benefits from hardware-assist via the IPP library.

That pretty much covers it and now we see commonality between compression and encryption. The commonality is mostly related to whether or not a query is being serviced via Smart Scan.

That’s Not All

If HCC data is also stored in encrypted form, a Smart Scan is able to filter out vast amount of encrypted data without even touching it. That is, HCC short-circuits a lot of decryption cost. And, even though Exadata is really fast, it is always faster to not do something at all than to shift into high gear and do it as fast as possible.

Exadata Database Machine X2-2 or X2-8? Sure! Why Not? Part I.

I’ve been getting a lot of questions about why one would choose Exadata Database Machine X2-8 over Exadata Database Machine X2-2. That’s actually a tough question, however, some topics do spring to mind. I’ll start a list:

  1. The Exadata Database Machine X2-8 only comes in full-rack configurations. No way to “start small.”
  2. The Exadata Database Machine X2-2 only (immediately) supports Oracle Linux. If Solaris is attractive to you then the X2-2 is not an option at the time of this blog entry. That is slated to change soon.
  3. Database Host RAM. The aggregate database grid RAM in a full-rack X2-2 system is 768 GB but 2 TB with the X2-8. The list is quite long for areas that benefit from the additional memory. Such topics as large user counts (consolidation or otherwise), join processing, and very large SGA come to mind. And, regarding large SGA, don’t forget, the Exadata Database Machine supports in-memory Parallel Query as well.

Not on the numbered list is the more sensitive topic of processor power. While these sorts of things are very workload-dependent, I’d go with 16 Intel Xeon 7500 (Nehalem EX) processors over 16 Intel Xeon 5600 (Westmere EP) for most any workload.

So, readers, what reasons would motivate you in one direction or the other?

Seven Fundamentals Everyone Should Know About Exadata Before Attending Exadata-Related Presentations.

I speak to a lot of customers, prospects and co-workers about Exadata.  Even though Exadata has been in production for two years I still do not presume everyone has a grasp of some of the more important fundamentals of Exadata. I’ll routinely get asked about how very large SGA buffering can enhance Exadata Smart Scan or how Storage Indexes might improve OLTP workloads and other such non sequiturs.

There are a lot of sessions about Exadata being offered at Oracle OpenWorld 2010 and for good reason.  Exadata is exciting technology! It dawns on me, however, that a few words explaining some of the more fundamental aspects of Exadata might help folks absorb more of what they are hearing in the sessions they attend next week.

I consider the following seven terms and definitions utterly important for folks to know before sitting through an Exadata presentation. In fact, there may even be some sessions offered by presenters who could also benefit from the following 242 words?

  • Cell Offload Processing.
    • Work performed by the Storage Servers that would otherwise have to be executed in the database grid. Includes functionality like Smart Scan, datafile initialization, RMAN offload, Hybrid Columnar Compression (HCC) decompression.
  • Smart Scan.
    • Most relevant Cell Offload Processing for improving Data Warehouse / Business Intelligence query performance. Smart Scan is the agent for offloading filtration, projection, Storage Index exploitation and HCC decompression.
  • Full Scan or Index Fast Full Scan.
    • The required access method chosen by the query optimizer in order to trigger a Smart Scan.
  • Direct Path Reads.
    • Required buffering model for a Smart Scan. The flow of data from a Smart Scan cannot be buffered in the SGA buffer pool. Direct path reads can be performed for both serial and parallel queries. Direct path reads are buffered in process PGA (heap).
  • Result Set.
    • Data returned by the SQL processing layer. The SQL processing layer is in the Oracle Database. The data flowing from a Smart Scan is not a result set.
  • Exadata Smart Flash Cache.
    • Flash Cache in each of the Storage Servers. Not to be confused with Database Flash Cache which is Flash in the database grid and not compatible with Exadata. Smart Scan aggressively scans both HDD and Flash media concurrently. When data is present in the flash cache scan rates of 50 GB/s on Exadata Version 2 hardware are the norm for full rack configurations.
  • Storage Index.
    • Dynamic, in-memory indexes. The role of Storage Index technology is not to aid in locating data faster but instead to eliminate I/O. With Storage Indexes the Exadata Storage Server software can determine whether or not a given storage region contains rows relevant to the query and decide to not read the storage region. Storage Indexes are only examined during a Smart Scan.

I hope you’ll find this helpful.


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All content is © Kevin Closson and "Kevin Closson's Blog: Platforms, Databases, and Storage", 2006-2013. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Kevin Closson and Kevin Closson's Blog: Platforms, Databases, and Storage with appropriate and specific direction to the original content.

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