My First Experience Running SLOB – Status Update 1

Posted in: Technical Track

Other SLOB-related are listed in “My SLOB IO testing index“.

NOTE: This is a copy of my G+ post from yesterday. You can find the original over here. As I am going to continue writing about our ongoing IO testing efforts on this blog, I decided to provide the first post here to give readers a bit more context.

Status – Work-in-progress. We are still working on testing and analyzing the results. However, there are some things that are worth sharing with others to help out with your efforts. This is why I chose to use G+ to publish some intermediate status update and possibly raise some discussion.

SLOB is The Simple Little Oracle Benchmark from +Kevin Closson.

Our attention to SLOB sparked during +Alex Gorbachev‘s and +Kevin Closson‘s Twitter discussion that more or less could be summarized by the following tweet:!/kevinclosson/statuses/200727040192823296

@alexgorbachev says to @kevinclosson: lots of the system IO bound below the CPU level so you should see similar number with Orion or SLOB. why don’t I test?

Amen! This is where we joined efforts with +Gwen Shapira to leverage +Pythian’s follow-the-sun model and a bit of powerful hardware to find the truth. We based ourselves on+Alex Gorbachev‘s assumption that Orion should show roughly the same numbers than SLOB and +Kevin Closson‘s claim that Orion could easily mislead us by giving way too optimistic results.

SLOB is nothing but a ~84MB schema with a table and index created in Oracle database to test LIO (if you set a big db_cache_size) or PIO (if you set a small db_cache). Well, by default, there are 128 schemas created with the same data structures.IMHO: It is a very good idea to test the performance by executing the same actions that most Applications do in a real live but make it so simple that it is application-agnostic.

However, Orion has a good advantage over SLOB as it doesn’t require any installation to start testing PIO. The advantage may skew the results in some cases. Our goal is to see how close the results will be at least on one particular system, and if the results are different, why.

—- Phase 1
Env: Oracle Linux Server release 5.8, RDBMS (64 bit)
We created SLOB DB using kindly prepared SLOB/misc/create_database_kit/README and a simple DB creation script. We also had to fix type “alter tablespace SLOB” to “alter tablespace IOPS” and increase processes from 100 to at least 200 as otherwise some schemas out of 128 were not created.

—- Phase 2
We executed several tests using simple syntax SLOB/ 0 12 (first parameter writers count, second parameter readers count). We executed the script with several different parameters starting from 4 and ending with 68.

—- Phase 3
We had a careful look at the results received and tried to find out if the results were comparable. This is where we got a bit of a surprise: SLOB was able to read 10000 8k blocks per second while Orion indicated 4305 IOPS (8k blocks IOs).

Further analysis revealed that the results has been dramatically impacted by Oracle IO requests enhancement. Instead of making single 8k blocks reads, Oracle put several (~20 on average) IO requests together and sent these packs to storage. Instead of the “db file sequential read” event, we saw “db file parallel read” on the top of Timed Foreground Events list.

Further research led us to the following MOS note: Some DB File Parallel Read Against An Empty Partition [ID 1367059.1].
It didn’t provide all the details on “db file parallel read” event, but it did direct us to the way to have Oracle avoid using “db file parallel read” and use “db file sequential read” instead.

The solution is to set the following hidden parameters. This makes Oracle forget about possible IO optimizations and keep going with single block random reads.

alter system set “_db_block_prefetch_limit”=0 scope=spfile;
alter system set “_db_block_prefetch_quota”=0 scope=spfile;
alter system set “_db_file_noncontig_mblock_read_count”=0 scope=spfile;

As of now, we have modified the default init.ora parameters, kindly provided by+Kevin Closson under SLOB/misc/create_database_kit/create.ora as follows:

Original Values

db_files = 300
processes = 100
memory_max_target = 2G


Our Values



Stay tuned! We are working though the testing now and will come with SLOB and Orion results soon.

BTW: Already we see that with fast CPUs (like we are running on that system), the CPU time an instance spends on block processing is within 1% of total time spent. Therefore, I predict that the Orion and SLOB results will be very close to each other.

Yury & Co :)

Want to talk with an expert? Schedule a call with our team to get the conversation started.

About the Author

Yury is a nice person who enjoys meeting and working with people on challenging projects in the Oracle space. He started to work as an Oracle DBA 14 years ago (1997). For the past 10 years (since 2001) his main area of expertise is Oracle e-Business Suite. Yury is an OCP 7,8,9,10g and OCM 9i,10g. He is a frequent presenter at Oracle related conferences such as Hotsos, UKOUG and AUOUG. Yury is a socially active person. Apart from Social Media (Twitter, Bloging, Facebook) he is the primary organizer of Sydney Oracle Meetup group (250 people). So if you happen to be in Sydney (Australia) drop Yury a message and stop by at one of his Meetups.

7 Comments. Leave new

My First Experience Running SLOB – Status Update 2 (first results) | The Pythian Blog
May 15, 2012 1:57 am

[…] +Alex Gorbachev and +Kevin Closson expected to see. You can find the first related blog post over here. It will give you the necessary context for further reading. Just to recap: +Kevin Closson says […]

Insider’s Guide to ODA Performance | The Pythian Blog
May 18, 2012 1:23 pm

[…] new benchmark tool and started using it to get more data about ODA performance, he already shared his experience and perliminary results. I expect he’ll share more over the next week or two, so watch our […]

My First Experience Running SLOB – Don’t repeat my errors (awr) | The Pythian Blog
May 19, 2012 10:36 am

[…] you are wondering what I am busy with then this post explains […]

My SLOB IO testing index | The Pythian Blog
May 20, 2012 8:36 pm

[…] Make data cache as small as possible. Don’t worry about any concurrency issues before you hit them. I set db_cache_size=12M and it didn’t give me any concurrency problems even with 128 readers test. Details are here. […]

My First Experience Running SLOB – ORION vs SLOB – 2:0 | The Pythian Blog
June 3, 2012 7:54 am

[…] Kevin Closson and Alex Gorbachev draw my attention. You can find the details on the discussion here. The conversation let me rethink if ORION is the right tool for the job. During the last few weeks […]

SLOB on steroids – Part 1 | The Pythian Blog
July 8, 2012 4:16 am

[…] it to ”db file parallel read” – How cool it is? I learn it while assessing SLOB testing results, 2. In RAC configuration sometimes you need to adjust gcs_server_processes init.ora […]

Collection of links, tips and tools for running SLOB | Pardy DBA
February 15, 2013 9:34 pm

[…] Disable Oracle IO optimization that turns your desired db file sequential reads into db file paralle…. Kevin Closson has also recommended use of these parameters in the simple init.ora file for read testing. I consider this a requirement, not a recommendation. I already mentioned this above but it’s worth repeating. […]


Leave a Reply

Your email address will not be published. Required fields are marked *