Monday Oct 19, 2009

Exadata V2... Oracle grid consolidation in a box

I spent some time last week at OOW talking with Oracle customers regarding the technology in the Exadata V2 database machine. There were certainly a lot of customers excited to use this for their data warehouses - 21GB/sec disk throughput, 50GB/sec flash cache, and Hybrid Columnar Compression really accelerate this machine past the competition. The viability of Exadata V2 for DW/BI was really a given, but what impressed me the most was the number of customers looking to consolidate applications in this environment.

Ever since I was first brought onto this project, I thought Exadata V2 would be an excellent platform for consolidation. In my experience working on the largest of Sun's servers, I have seen customers with dozens of instances on a single machine. Using M9000 series machines, you can create domains in order to support multiple environments - this very much mirrors what Exadata V2 can provide. Exadata V2 allows DBAs to deploy multiple instances across a grid of RAC nodes available in the DB machine – and since you are using RAC, availability is a given. Also, the addition of Flash allows for up to 1 million IOPs to support your ERP/OLTP environments. Consider the picture below.

With this environment, your production data warehouse can share the same infrastructure as the ERP, test, and development environments. This model allows the flexibility to add/subtract nodes from a particular database as needed. But, the operational efficiency is not the biggest benefit to consolidation. The savings in terms of power, space, and cooling are substantial.

Consider for a moment the number of drives necessary to match the 1 million IOPs available in the database machine. Assuming you are using the best 15,000 rpm drive, you would be able to do 250 IOPs/drive. So, to get to 1 million IOPs, you would need 4,000 drives! A highly dense 42U storage rack can house any where from 300-400 drives. So, you would need 10 racks, just for the storage and at least one rack for servers.

With Exadata V2, you get more than 10:1 savings in floor space and all the power an cooling benefits as well. It is no wonder people are excited about Exadata V2 as a platform to consolidate compute and storage resources.

Friday Sep 25, 2009

Jumbo Frames with Oracle RAC really does Rock!!

I have been involved in a customer situation on and off for at least 6 months now. The customer had been seeing performance issues with their application running on Oracle 10g RAC. We looked through the mounds of data initially and noticed that they were indeed waiting quite a bit on Global cache buffer waits. This was during times of fairly heavy load and we could see the CPU was fairly busy with interrupts as well. After looking at the MTU size for the cluster interconnect, we noticed that it was incorrectly set to the default (1500). Thus started the odyssey to implement Jumbo Frames.

The default MTU is 1500 for Solaris, but this is not ideal when Oracle is using an 8K block size. Simple math tells us that you will require 6 transfers to transmit just one block of data across the cluster interconnect. This just creates additional overhead on the server and additional latency waiting for global blocks to be transferred. Changing the MTU to be a "jumbo frame" of 8K or greater is fairly simple from a technical point of view, but it can quickly turn into a political issue.

The cluster interconnect is often relegated to be the responsibility of the networking group. No problem right? While this is a network component, it is really part of the server - no different really from a PCI bus or processor back plane. The networking groups will often apply their tried and true methods for LANs around the company, but this doesn't translate to RAC. Modern network switches can easily handle this configuration change as well, but policy often wins. The networking group assures everyone their switch can handle the traffic with the default MTU and everyone goes on their merry way.

So, what happened?

After months looking at "other things", they finally were convinced to try this "Best Practice" with Jumbo Frames. Immediately, they saw:

  • 50% reduction in CPU overhead
  • 75% reduction in Global cache buffer waits
  • IP Reassemblies dropped by 10x

Moral of the story: Implement Jumbo Frames for Oracle RAC interconnects... It is a best practice after all :)

Monday Jun 11, 2007

Swing and a miss... Benchmarking is not \*that\* easy.

I applaud tools that aim to make life easier. The cell phone is a wonderful invention that when combined with my palm pilot was wonderful. Now Apple has taken it as step further with the music, movies, internet and birthed the iPhone - nicer still!

Over the past year, I have been seeing more and more IT shops experiment with benchmark tools. One such tool is a kit developed by Dominic Giles of Oracle called Swingbench. Swingbench is a benchmark toolkit that is easy to install and run. Now the DBA can install the benchmark schema and with a few clicks... Wham they are benchmarking! Now comes the hard part - What do these results mean?

After about the 4th call of a customer having performance issues with their application "Swingbench", I was compelled to take a deeper look.

Luckily, all of the performance problems were easily solved by someone who benchmarks for a living. They were typically misconfiguration issues like: filesystem features, lack of io, lack of memory, too small of a dataset, ect... The scary part, these situations all used the supplied "demo" schema's.

By pursuing the Swingbench documentation, I saw that the demo schema's top out at a 100GB database size. This is also alarming. Most IT shops that buy servers or deploy multi-node RAC configurations have more disk than the modern laptop. So you can imagine my surprise when I saw a bake-off of an enterprise class machine that is essentially doing no IO and choking to death on latches... simply the wrong test for the environment.

Event                                               Waits    Time (s) Ela Time
-------------------------------------------- ------------ ----------- --------
latch free                                      4,542,675   1,137,914    79.04
log file sync                                     242,359     164,671    11.44
buffer busy waits                                 102,540      61,887     4.30
enqueue                                            35,142      42,498     2.95
CPU time                                                       25,310     1.76

Benchmarking, is simply not \*that\* easy. It takes time to scale up a workload that can simulate your environment. No question that Swingbench gives you a nice head start. It allows you to encapsulate your transactions, run simple regression tests, but you have to take the time to customize the kit to include your data and transactions. The demo schema's are simply a starting point.
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This blog discusses performance topics as running on Sun servers. The main focus is in database performance and architecture but other topics can and will creep in.

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