Archive for the 'Oracle11g RAC' Category

SLOB Physical I/O Randomness. How Random Is Random? Random!

I recently read a blog post by Kyle Hailey regarding some lack of randomness he detected in the Orion I/O generator tool. Feel free to read Kyle’s post but in short he used dtrace to detect Orion was obliterating a very dense subset of the 96GB file Orion was accessing.

I’ve used Orion for many years and, in fact, wrote my first Orion related blog entry about 8 years ago. I find Orion to be useful for some things and of course DBAs must use Orion’s cousin CALIBRATE_IO as a part of their job. However, neither of these tools perform database I/O. If you want to see how database I/O behaves on a platform it’s best to use a database. So, SLOB it is. But wait! Is SLOB is just another storage cache-poking randomness-challenged distraction from your day job? No, it isn’t.

But SLOB Is So Very Difficult To Use

It’s quite simple actually. You can see how simple SLOB is to set up and test by visiting my picture tutorial.

How Random Is Random? Random!

SLOB is utterly random. However, there are some tips I’d like to offer in this post to show you how you can choose even higher levels of randomness in your I/O testing.

Kyle used dtrace and some shell commands to group block visits into buckets. Since I’m analyzing the randomness of SLOB I’ll use a 10046 trace on the database sessions. First I’ll run a 96 user SLOB test with slob.conf->UPDATE_PCT=0.

After the SLOB test was completed I scrambled around to find the trace files and worked out a simple set of sed(1) expressions to spit out the block numbers being visited by each I/O of type db file sequential read:


I then grouped the blocks being visited into buckets much the same way Kyle did in his post:


I’ll show some analysis of the those buckets later in the post.  Yes, SLOB is random as analysis of 96u.blocks.txt will show but it can be even more random if one configures a RECYCLE buffer pool. One of the lesser advertised features of SLOB is the fact that all working tables in the SLOB schemas are created with BUFFER_POOL RECYCLE in the storage clause. The idea behind this is to support the caching of index blocks in the SGA buffer pool. When no RECYCLE pool is allocated there is a battle for footprint in the SGA buffer pool causing even buffers with index blocks to be reused for buffering table/index blocks of the active transactions. Naturally when indexes are not cached there will be slight hot-spots for constant, physical, re-reads of the index blocks. The question becomes what percentage of the I/O do these hot blocks account for?

To determine how hot index blocks are I allocated a recycle buffer pool and ran another 2 minute SLOB test. As per the following screen shot I again grouped block visits into buckets:


After having both SLOB results (with and without RECYCLE buffer pool) I performed a bit of text processing to determine how different the access patterns were in both scenarios. The following shows:

  • The vast majority of blocks are visited 10 or less times in both models
  • The RECYCLE pool model clearly flattens out the re-visit rates as the hotest block is visited only 12 times compared to the 112 visits for the hottest block in the default case
  • If 12 is the golden standard for sparsity (as per the RECYCLE pool test case) then even the default is quite sparse because dense buckets accounted for only 84,583 physical reads compared to the nearly 14 million reads of blocks in the sparse buckets


The following table presents the data including the total I/O operations traced. The number of sparse visits are those blocks that were accessed less than or equal to 10 times during the SLOB test. I should point out that there will naturally be more I/O during a SLOB test when index accesses are forced physical as is the case with the default buffer pools. That is, the RECYCLE buffer pool case will have a slightly higher logical I/O rate (cache hits) due to index buffer accesses.



If you want to know how database I/O performs on a platform use a database. If using a database to test I/O on a platform then by all means drive it with SLOB ( a database I/O tool).

Regarding randomness, even in the default case SLOB proves itself to be very random. If you want to push for even more randomness then the way forward is to configure db_recycle_cache_size.

Enjoy SLOB! The best place to start with SLOB is the SLOB Resources Page.







Oracle’s Timeline, Copious Benchmarks And Internal Deployments Prove Exadata Is The Worlds First (Best?) OLTP Machine – Part 1.5

In Part I of this series about Oracle OLTP/ERP on Exadata versus non-Exadata, I took a moment to point out the inaccuracies of a particular piece of Oracle marketing literature. In a piece aimed at chronicling Oracle Corporation history, the marketing department went way out of line by making the following claim regarding Exadata:

[…] wins benchmarks against key competitors [..]

Please don’t get me wrong, those five words appearing in any random sentence wouldn’t pose any sort of  a problem. However, situated as they are in this particular sentence does create a  problem because the statement is utterly false.  Exadata has not won a single benchmark against any competitor–“key” or otherwise.

Along For The Ride
In Part I of this series I pointed out the fact HP Oracle Exadata Storage Server cells (a.k.a., V1 Exadata) were used in this June 2009 HP BladeSystem 1-TB Scale TPC-H. However, merely involving Exadata hardware can hardly support Oracle’s marketing claim vis a vis winning benchmarks against key competitors.

There is a big difference between being involved in a benchmark and being the technology that contributes to the result.

I made it clear, in Part I, that Exadata storage was used in that 2009 HP TPC-H result but none of the Exadata features contributed to the result. I clarified that assertion by pointing out that the particular benchmark in question was an In-memory Parallel Query result. Since the result establish Oracle database performance achieved through in-memory database processing I didn’t feel compelled to shore up my assertion. I didn’t think anyone would be confused over the fact that in-memory database processing is not improved by storage technology.

I was wrong.

In the comment section of Part I a comment by a blog reader took offense at my audacious claim. Indeed, how could I assert that storage is not a relevant component in achieving good in-memory database processing benchmark results. The reader stated:

You give reference to a TPHC that used Exadata and then say no Exadata features were used. [..] You obviously don’t know what you are talking about

Having seen that I began to suspect there may be other readers confused on the matter so I let the comment through moderation and decided to address the confusion it in this post.

So now it’s time to address the reader’s comment. If Exadata is used in a benchmark, but Exadata Storage Server offload processing is disabled, would one consider that an Exadata benchmark or was Exadata merely along for the ride?

Here is a screenshot of the full disclosure report that shows Exadata storage intelligence (offload processing) features were disabled. For this reason I assert that Exadata has never won a benchmark against “competitors”, neither “key” nor otherwise.

The screenshot:

Yet Another Excellent RAC Install Guide

Tim Hall sent me email to point me to a recent step-by-step install tip he produced for Oracle11g with NAS storage (NFS).  In the email he asked me if I had any experience with the new Oracle11g Direct NFS (DNFS) feature. The answer is, yes, I have a lot of DNFS experience as I hinted to with my blog post entitled Manly Men Only Deploy Oracle With Fibre Channel Part VI. Introducing Oracle11g Direct NFS. If I haven’t plugged the “Manly Man” series lately I am doing so again now. I think anyone interested in storage with an Oracle slant would take interest.  The full series of Manly Man posts can be found easily through my index of CFS/NFS/ASM Topics as well as this entry about a recent Oracle 300GB TPC-H result. That TPC-H result is very interesting-especially if you are trying to get out of SAN/DAS/NAS rehab. Yes, that was supposed to be humorous.

Back to the point. Here is the link to Tim’s (very good) step-by-step Oracle Database 11g RAC on Linux setup for NFS environments. I especially liked the mention of Direct NFS since I think it is very important technology as my jointly-authored Oracle Whitepaper on the topic should attest.

Improved Linux Real Application Clusters Clusterware Installation with Oracle Database 11g

Just a quick blog entry. I have installed 11g RAC quite a few times already and just wanted to share with you folks an observation.

Those of you who have installed 10gR2 Clusterware (CRS) know that towards the end of the CRS installation you have to go from node to node and execute $ORA_CRS_HOME/ When you run it on the last node the script will try to set up VIPs (this is why you have to run the CRS as root in an xterm because it is a window-less JAVA app). Oracle1gR2 has had an annoying bug in it that failed the VIP setup because it was very picky about the IP addresses you assigned to VIPs. The workaround for that was to ignore the problem and then invoke $ORA_CRS_HOME/bin/vipca and walk through the setup of VIPs (including GSD and so on). It was a minor problem that was easy to work around.

10g and 11g Clusterware Co-Existence

I have not seen that problem with 11g. In fact, the reason I’m blogging this is because I just walked through an install of 10gR2 Clusterware on my cluster running x86 RHEL4 attached to NAS (NFS). I need a setup where I have both 10g and 11g clusterware installed and I need to be able to “hide” and “expose” either with a few simple commands to test one or the other. After the successful install of 10gR2 CRS, I “hid it” (to include all the residue in /etc) and proceeded to install 11g CRS. Since I just did both 10gR2 CRS and 11g CRS installs back to back I was reminded that 10gR2 CRS has that pesky problem and I did have to hand-invoke vipca to get through it. I was pleasantly reminded, however, that 11g does not have that problem.

For those of you who are used to seeing the complaint about VIPs at the conclusion of the last execution, see the following screen shot from 11g and breathe a sigh of relief.


And a picture speaks a thousand words so here is a shot of my little 11g NAS RAC clusterware setup:


Note to self: Investigate whether 11g CRS works with 10gR2 RAC instances and make a blog entry. It should, so I will.


I work for Amazon Web Services. The opinions I share in this blog are my own. I'm *not* communicating as a spokesperson for Amazon. In other words, I work at Amazon, but this is my own opinion.

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All content is © Kevin Closson and "Kevin Closson's Blog: Platforms, Databases, and Storage", 2006-2015. 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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