Tag: distributed systems

Parallel Programming: Logical Clocks

In a distributed system nodes can talk (cooperate) to each other and coordinate their systems.  However, the different nodes can execute concurrently, there is no global clock in which all nodes function on, and some of these nodes can fail independently (Sandén, 2011).  Since nodes talk to each other, we must study them as they interact with each other.  Thus, a need to use logical clocks (because we don’t have global clocks) which show that distances in time are lost (Sandén, 2011). In logical clocks: all nodes agree on an order of events, partially (where something can happen before another event).  They only describe the order of events, not with respect to time.  If nodes are completely disjoint in a logical clock, then a node can fail independently. This is one way to visualize the complex nature of nodes.

The following is an example of a logical clock:

Capture

Reference

Adv Topics: Distributed Programing

Distributed programming can be divided into the following two models:

  • Shared memory distributed programming: Is where serialized programs run on multiple threads, where all the threads have access to the underlying data that is stored in shared memory (Sakr, 2014). Each thread should be synchronized as to ensure that read and write functions aren’t being done on the same segment of the shared data at the same time. Sandén (2011) and Sakr, (2014) stated that this could be achieved via semaphores (signals other threads that data is being written/posted and other threads should wait to use the data until a condition is met), locks (data can be locked or unlocked from reading and writing), and barriers (threads cannot run on this next step until everything preceding it is completed). A famous example of this style of parallel programming is the use of MapReduce on data stored in the Hadoop Distributed File System (HDFS) (Lublinsky, Smith, & Yakubovich, 2013; Sakr, 2014). The HDFS is where the data is stored, and the mapper and reducers functions can access the data stored in the HDFS.
  • Message passing distributed programming: Is where data is stored in one location, and a master thread helps spread chunks of the data onto sub-tasks and threads to process the overall data in parallel (Sakr, 2014).       There are explicitly direct send and receive messages that have synchronized communications (Lublinsky et al., 2013; Sakr, 2014).   At the end of the runs, data is the merged together by the master thread (Sakr, 2014). A famous example of this style of parallel programming is Message Passing Interface (MPI), such that many weather models like the Weather Research and Forecasting (WRF) model benefits use this form of distributed programming (Sakr, 2014; WRF, n.d.). The initial weather conditions are stored in one location and are chucked into small pieces and spread across the threads, which are then eventually joined in the end to produce one cohesive forecast.

However, there are six challenges to distributed programming model: Heterogeneity, Scalability, Communications, Synchronization, Fault-tolerance, and Scheduling (Sakr, 2014). Each of these six challenges is interrelated. Thus, an increase in complexity in one of these challenges can increase the level of complexity of one or more of the other ones. Therefore, both the shared memory and message passing distributed programming are insufficient when processing the large-scale data in cloud computing environment. This post will focus on two of these six:

  • Scalability issues exist when an increase in the number of users, the amount of data, and request for resources and the distributed processing system can still be effective (Sakr, 2014). Using Hadoop and HDFS in the cloud allows for a mitigation of the scalability issues by providing a free open-source way of managing such an explosion of data and demand on resources. But, the storage costs on the cloud will also increase, even though it is usually 10% of the cost than normal information technology infrastructure (Minelli, Chambers, & Dhiraj, 2013). As the scale of resources increase, it can also increase a number of resources needed for a deal with communication and synchronization (Sakr, 2014).
  • Synchronization is a critical challenge that must be addressed because multiple threads should be able to share data without corrupting the data or cause inconsistencies (Sandén, 2011; Sakr, 2014). Lublinsky et al. (2013), stated that MapReduce requires proper synchronization between the mapper and reducer functions to work. Improper synchronization can lead to issues in fault tolerance. Thus, efficient synchronization between reading and write operations are vital and are within the control of the programmers (Sakr, 2014). The challenge comes when scalability issues are introduced and applying synchronization methods without degrading performances, causing deadlocks where two tasks want access to the same data, load balancing issues, or wasteful use of computational resources (Lublinsky et al., 2013; Sandén, 2011; Sakr, 2014).

Resources

  • Lublinsky, B., Smith, K. T., & Yakubovich, A. (2013). Professional Hadoop Solutions. Vitalbook file.
  • Minelli, M., Chambers, M., & Dhiraj, M. (2013) Big Data, Big Analytics: Emerging Business Intelligence and Analytic Trends for Today’s Businesses. John Wiley & Sons P&T. VitalBook file.
  • Sandén, B. I. (2011) Design of Multithreaded Software: The Entity-Life Modeling Approach. Wiley-Blackwell. VitalBook file.
  • Sakr, S. (2014). Large Scale and Big Data, (1st ed.). Vitalbook file.

Big Data Analytics: Compelling Topics

Big Data and Hadoop:

According to Gray et al. (2005), traditional data management relies on arrays and tables in order to analyze objects, which can range from financial data, galaxies, proteins, events, spectra data, 2D weather, etc., but when it comes to N-dimensional arrays there is an “impedance mismatch” between the data and the database.    Big data, can be N-dimensional, which can also vary across time, i.e. text data (Gray et al., 2005). Big data, by its name, is voluminous. Thus, given the massive amounts of data in Big Data that needs to get processed, manipulated, and calculated upon, parallel processing and programming are there to use the benefits of distributed systems to get the job done (Minelli, Chambers, & Dhiraj, 2013).  Parallel processing allows making quick work on a big data set, because rather than having one processor doing all the work, you split up the task amongst many processors.

Hadoop’s Distributed File System (HFDS), breaks up big data into smaller blocks (IBM, n.d.), which can be aggregated like a set of Legos throughout a distributed database system. Data blocks are distributed across multiple servers. Hadoop is Java-based and pulls on the data that is stored on their distributed servers, to map key items/objects, and reduces the data to the query at hand (MapReduce function). Hadoop is built to deal with big data stored in the cloud.

Cloud Computing:

Clouds come in three different privacy flavors: Public (all customers and companies share the all same resources), Private (only one group of clients or company can use a particular cloud resources), and Hybrid (some aspects of the cloud are public while others are private depending on the data sensitivity.  Cloud technology encompasses Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS).  These types of cloud differ in what the company managers on what is managed by the cloud provider (Lau, 2011).  Cloud differs from the conventional data centers where the company managed it all: application, data, O/S, virtualization, servers, storage, and networking.  Cloud is replacing the conventional data center because infrastructure costs are high.  For a company to be spending that much money on a conventional data center that will get outdated in 18 months (Moore’s law of technology), it’s just a constant sink in money.  Thus, outsourcing the data center infrastructure is the first step of company’s movement into the cloud.

Key Components to Success:

You need to have the buy-in of the leaders and employees when it comes to using big data analytics for predictive, prescriptive or descriptive purposes.  When it came to buy-in, Lt. Palmer had to nurture top-down support as well as buy-in from the bottom-up (ranks).  It was much harder to get buy-in from more experienced detectives, who feel that the introduction of tools like analytics, is a way to tell them to give up their long-standing practices and even replace them.  So, Lt. Palmer had sold Blue PALMS as “What’s worked best for us is proving [the value of Blue PALMS] one case at a time, and stressing that it’s a tool, that it’s a compliment to their skills and experience, not a substitute”.  Lt. Palmer got buy-in from a senior and well-respected officer, by helping him solve a case.  The senior officer had a suspect in mind, and after feeding in the data, the tool was able to predict 20 people that could have done it in an order of most likely.  The suspect was on the top five, and when apprehended, the suspect confessed.  Doing, this case by case has built the trust amongst veteran officers and thus eventually got their buy in.

Applications of Big Data Analytics:

A result of Big Data Analytics is online profiling.  Online profiling is using a person’s online identity to collect information about them, their behaviors, their interactions, their tastes, etc. to drive a targeted advertising (McNurlin et al., 2008).  Profiling has its roots in third party cookies and profiling has now evolved to include 40 different variables that are collected from the consumer (Pophal, 2014).  Online profiling allows for marketers to send personalized and “perfect” advertisements to the consumer, instantly.

Moving from online profiling to studying social media, He, Zha, and Li (2013) stated their theory, that with higher positive customer engagement, customers can become brand advocates, which increases their brand loyalty and push referrals to their friends, and approximately 1/3 people followed a friend’s referral if done through social media. This insight came through analyzing the social media data from Pizza Hut, Dominos and Papa Johns, as they aim to control more of the market share to increase their revenue.  But, is this aiding in protecting people’s privacy when we analyze their social media content when they interact with a company?

HIPAA described how we should conduct de-identification of 18 identifiers/variables that would help protect people from ethical issues that could arise from big data.   HIPAA legislation is not standardized for all big data applications/cases; it is good practice. However, HIPAA legislation is mostly concerned with the health care industry, listing those 18 identifiers that have to be de-identified: Names, Geographic data, Dates, Telephone Numbers, VIN, Fax, Device ID and serial numbers, emails addresses, URLs, SSN, IP address, Medical Record Numbers, Biometric ID (fingerprints, iris scans, voice prints, etc), full face photos, health plan beneficiary numbers, account numbers, any other unique ID number (characteristic, codes, etc), and certifications/license numbers (HHS, n.d.).  We must be aware that HIPAA compliance is more a feature of the data collector and data owner than the cloud provider.

HIPAA arose from the human genome project 25 years ago, where they were trying to sequence its first 3B base pair of the human genome over a 13 year period (Green, Watson, & Collins, 2015).  This 3B base pair is about 100 GB uncompressed and by 2011, 13 quadrillion bases were sequenced (O’Driscoll et al., 2013). Studying genomic data comes with a whole host of ethical issues.  Some of those were addressed by the HIPPA legislation while other issues are left unresolved today.

One of the ethical issues that arose were mentioned in McEwen et al. (2013), for people who have submitted their genomic data 25 years ago can that data be used today in other studies? What about if it was used to help the participants of 25 years ago to take preventative measures for adverse health conditions?  However, ethical issues extend beyond privacy and compliance.  McEwen et al. (2013) warn that data has been collected for 25 years, and what if data from 20 years ago provides data that a participant can suffer an adverse health condition that could be preventable.  What is the duty of the researchers today to that participant?

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