What is the best kind of IO? The one you do not have to do
By Greg Schulz
If no IO (input/output) operation is the best IO, than the second best IO is the one that can be done as close to the application and processor with best locality of reference. Then the third best IO is the one that can be done in less time, or at least cost or impact to the requesting application which means moving further down the memory and storage stack (figure 1).
Figure 1 memory and storage hierarchy
The problem with IO is that they are basic operation to get data into and out of a computer or processor so they are required; however, they also have an impact on performance, response or wait time (latency). IO require CPU or processor time and memory to set up and then process the results as well as IO and networking resources to move data to their destination or retrieve from where stored. While IOs cannot be eliminated, their impact can be greatly improved or optimized by doing fewer of them via caching, grouped reads or writes (pre-fetch, write behind) among other techniques and technologies.
Think of it this way, instead of going on multiple errands, sometimes you can group multiple destinations together making for a shorter, more efficient trip; however, that optimization may also take longer. Hence sometimes it makes sense to go on a couple of quick, short low latency trips vs. one single larger one that takes half a day however accomplishes many things. Of course, how far you have to go on those trips (e.g. locality) makes a difference of how many you can do in a given amount of time.
What is locality of reference?
Locality of reference refers to how close (e.g location) data exists for where it is needed (being referenced) for use. For example, the best locality of reference in a computer would be registers in the processor core, then level 1 (L1), level 2 (L2) or level 3 (L3) onboard cache, followed by dynamic random access memory (DRAM). Then would come memory also known as storage on PCIe cards such as nand flash solid state device (SSD) or accessible via an adapter on a direct attached storage (DAS), SAN or NAS device. In the case of a PCIe nand flash SSD card, even though physically the nand flash SSD is closer to the processor, there is still the overhead of traversing the PCIe bus and associated drivers. To help offset that impact, PCIe cards use DRAM as cache or buffers for data along with Meta or control information to further optimize and improve locality of reference. In other words, help with cache hits, cache use and cache effectiveness vs. simply boosting cache utilization.
CIO, CTO & Developer Resources
What can you do the cut the impact of IO
Establish baseline performance and availability metrics for comparison
Realize that IOs are a fact of IT virtual, physical and cloud life
Understand what is a bad IO along with its impact
Identify why an IO is bad, expensive or causing an impact
Find and fix the problem, either with software, application or database changes
Throw more software caching tools, hyper visors or hardware at the problem
Hardware includes faster processors with more DRAM and fast internal busses
Leveraging local PCIe flash SSD cards for caching or as targets
Utilize storage systems or appliances that have intelligent caching and storage optimization capabilities (performance, availability, capacity).
Compare changes and improvements to baseline, quantify improvement
Greg Schulz is founder of the Server and StorageIO (StorageIO) Group, an IT industry analyst and consultancy firm. Greg has worked with various server operating systems along with storage and networking software tools, hardware and services. Greg has worked as a programmer, systems administrator, disaster recovery consultant, and storage and capacity planner for various IT organizations. He has worked for various vendors before joining an industry analyst firm and later forming StorageIO.
In addition to his analyst and consulting research duties, Schulz has published over a thousand articles, tips, reports and white papers and is a sought after popular speaker at events around the world. Greg is also author of the books Resilient Storage Network (Elsevier) and The Green and Virtual Data Center (CRC). His blog is at www.storageioblog.com and he can also be found on twitter @storageio.
Niklas Bjorkman wrote: Firstly I agree with your conclusion. NewSQL takes the best of the traditional databases and NoSQL databases to combine the benefits of both worlds. I do not agree that NewSQL vendors focus on giving scale-out features to transactional data. The NewSQL market is focusing on giving true ACID support combined with extreme performance, stepping away from the traditional relational structures in databases. A lot of developers appreciate the ease of accessing data using SQL and I think we will see more and more databases supporting standard SQL.
As you said - NewSQL databases often maintain the...
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