Tag Archive for: Data Warehouse

Benjamin Aunkofer

CAP Theorem

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Understanding databases for storing, updating and analyzing data requires the understanding of the CAP Theorem. This is the second article of the article series Data Warehousing Basics.

Understanding NoSQL Databases by the CAP Theorem

CAP theorem – or Brewer’s theorem – was introduced by the computer scientist Eric Brewer at Symposium on Principles of Distributed computing in 2000. The CAP stands for Consistency, Availability and Partition tolerance.

  • Consistency: Every read receives the most recent writes or an error. Once a client writes a value to any server and gets a response, it is expected to get afresh and valid value back from any server or node of the database cluster it reads from.
    Be aware that the definition of consistency for CAP means something different than to ACID (relational consistency).
  • Availability: The database is not allowed to be unavailable because it is busy with requests. Every request received by a non-failing node in the system must result in a response. Whether you want to read or write you will get some response back. If the server has not crashed, it is not allowed to ignore the client’s requests.
  • Partition tolerance: Databases which store big data will use a cluster of nodes that distribute the connections evenly over the whole cluster. If this system has partition tolerance, it will continue to operate despite a number of messages being delayed or even lost by the network between the cluster nodes.

CAP theorem applies the logic that  for a distributed system it is only possible to simultaneously provide  two out of the above three guarantees. Eric Brewer, the father of the CAP theorem, proved that we are limited to two of three characteristics, “by explicitly handling partitions, designers can optimize consistency and availability, thereby achieving some trade-off of all three.” (Brewer, E., 2012).

CAP Theorem Triangle

To recap, with the CAP theorem in relation to Big Data distributed solutions (such as NoSQL databases), it is important to reiterate the fact, that in such distributed systems it is not possible to guarantee all three characteristics (Availability, Consistency, and Partition Tolerance) at the same time.

Database systems designed to fulfill traditional ACID guarantees like relational database (management) systems (RDBMS) choose consistency over availability, whereas NoSQL databases are mostly systems designed referring to the BASE philosophy which prefer availability over consistency.

The CAP Theorem in the real world

Lets look at some examples to understand the CAP Theorem further and provewe cannot create database systems which are being consistent, partition tolerant as well as always available simultaniously.

AP – Availability + Partition Tolerance

If we have achieved Availability (our databases will always respond to our requests) as well as Partition Tolerance (all nodes of the database will work even if they cannot communicate), it will immediately mean that we cannot provide Consistency as all nodes will go out of sync as soon as we write new information to one of the nodes. The nodes will continue to accept the database transactions each separately, but they cannot transfer the transaction between each other keeping them in synchronization. We therefore cannot fully guarantee the system consistency. When the partition is resolved, the AP databases typically resync the nodes to repair all inconsistencies in the system.

A well-known real world example of an AP system is the Domain Name System (DNS). This central network component is responsible for resolving domain names into IP addresses and focuses on the two properties of availability and failure tolerance. Thanks to the large number of servers, the system is available almost without exception. If a single DNS server fails,another one takes over. According to the CAP theorem, DNS is not consistent: If a DNS entry is changed, e.g. when a new domain has been registered or deleted, it can take a few days before this change is passed on to the entire system hierarchy and can be seen by all clients.

CA – Consistency + Availability

Guarantee of full Consistency and Availability is practically impossible to achieve in a system which distributes data over several nodes. We can have databases over more than one node online and available, and we keep the data consistent between these nodes, but the nature of computer networks (LAN, WAN) is that the connection can get interrupted, meaning we cannot guarantee the Partition Tolerance and therefor not the reliability of having the whole database service online at all times.

Database management systems based on the relational database models (RDBMS) are a good example of CA systems. These database systems are primarily characterized by a high level of consistency and strive for the highest possible availability. In case of doubt, however, availability can decrease in favor of consistency. Reliability by distributing data over partitions in order to make data reachable in any case – even if computer or network failure – meanwhile plays a subordinate role.

CP – Consistency + Partition Tolerance

If the Consistency of data is given – which means that the data between two or more nodes always contain the up-to-date information – and Partition Tolerance is given as well – which means that we are avoiding any desynchronization of our data between all nodes, then we will lose Availability as soon as only one a partition occurs between any two nodes In most distributed systems, high availability is one of the most important properties, which is why CP systems tend to be a rarity in practice. These systems prove their worth particularly in the financial sector: banking applications that must reliably debit and transfer amounts of money on the account side are dependent on consistency and reliability by consistent redundancies to always be able to rule out incorrect postings – even in the event of disruptions in the data traffic. If consistency and reliability is not guaranteed, the system might be unavailable for the users.

CAP Theorem Venn Diagram

Conclusion

The CAP Theorem is still an important topic to understand for data engineers and data scientists, but many modern databases enable us to switch between the possibilities within the CAP Theorem. For example, the Cosmos DB von Microsoft Azure offers many granular options to switch between the consistency, availability and partition tolerance . A common misunderstanding of the CAP theorem that it´s none-absoluteness: “All three properties are more continuous than binary. Availability is continuous from 0 to 100 percent, there are many levels of consistency, and even partitions have nuances. Exploring these nuances requires pushing the traditional way of dealing with partitions, which is the fundamental challenge. Because partitions are rare, CAP should allow perfect C and A most of the time, but when partitions are present or perceived, a strategy is in order.” (Brewer, E., 2012).

Benjamin Aunkofer

ACID vs BASE Concepts

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Understanding databases for storing, updating and analyzing data requires the understanding of two concepts: ACID and BASE. This is the first article of the article series Data Warehousing Basics.

The properties of ACID are being applied for databases in order to fulfill enterprise requirements of reliability and consistency.

ACID is an acronym, and stands for:

  • Atomicity – Each transaction is either properly executed completely or does not happen at all. If the transaction was not finished the process reverts the database back to the state before the transaction started. This ensures that all data in the database is valid even if we execute big transactions which include multiple statements (e. g. SQL) composed into one transaction updating many data rows in the database. If one statement fails, the entire transaction will be aborted, and hence, no changes will be made.
  • Consistency – Databases are governed by specific rules defined by table formats (data types) and table relations as well as further functions like triggers. The consistency of data will stay reliable if transactions never endanger the structural integrity of the database. Therefor, it is not allowed to save data of different types into the same single column, to use written primary key values again or to delete data from a table which is strictly related to data in another table.
  • Isolation – Databases are multi-user systems where multiple transactions happen at the same time. With Isolation, transactions cannot compromise the integrity of other transactions by interacting with them while they are still in progress. It guarantees data tables will be in the same states with several transactions happening concurrently as they happen sequentially.
  • Durability – The data related to the completed transaction will persist even in cases of network or power outages. Databases that guarante Durability save data inserted or updated permanently, save all executed and planed transactions in a recording and ensure availability of the data committed via transaction even after a power failure or other system failures If a transaction fails to complete successfully because of a technical failure, it will not transform the targeted data.

ACID Databases

The ACID transaction model ensures that all performed transactions will result in reliable and consistent databases. This suits best for businesses which use OLTP (Online Transaction Processing) for IT-Systems such like ERP- or CRM-Systems. Furthermore, it can also be a good choice for OLAP (Online Analytical Processing) which is used in Data Warehouses. These applications need backend database systems which can handle many small- or medium-sized transactions occurring simultaneous by many users. An interrupted transaction with write-access must be removed from the database immediately as it could cause negative side effects impacting the consistency(e.g., vendors could be deleted although they still have open purchase orders or financial payments could be debited from one account and due to technical failure, never credited to another).

The speed of the querying should be as fast as possible, but even more important for those applications is zero tolerance for invalid states which is prevented by using ACID-conform databases.

BASE Concept

ACID databases have their advantages but also one big tradeoff: If all transactions need to be committed and checked for consistency correctly, the databases are slow in reading and writing data. Furthermore, they demand more effort if it comes to storing new data in new formats.

In chemistry, a base is the opposite to acid. The database concepts of BASE and ACID have a similar relationship. The BASE concept provides several benefits over ACID compliant databases asthey focus more intensely on data availability of database systems without guarantee of safety from network failures or inconsistency.

The acronym BASE is even more confusing than ACID as BASE relates to ACID indirectly. The words behind BASE suggest alternatives to ACID.

BASE stands for:

  • Basically Available – Rather than enforcing consistency in any case, BASE databases will guarantee availability of data by spreading and replicating it across the nodes of the database cluster. Basic read and write functionality is provided without liabilityfor consistency. In rare cases it could happen that an insert- or update-statement does not result in persistently stored data. Read queries might not provide the latest data.
  • Soft State – Databases following this concept do not check rules to stay write-consistent or mutually consistent. The user can toss all data into the database, delegating the responsibility of avoiding inconsistency or redundancy to developers or users.
  • Eventually Consistent –No guarantee of enforced immediate consistency does not mean that the database never achieves it. The database can become consistent over time. After a waiting period, updates will ripple through all cluster nodes of the database. However, reading data out of it will stay always be possible, it is just not certain if we always get the last refreshed data.

All the three above mentioned properties of BASE-conforming databases sound like disadvantages. So why would you choose BASE? There is a tradeoff compared to ACID. If databases do not have to follow ACID properties then the database can work much faster in terms of writing and reading from the database. Further, the developers have more freedom to implement data storage solutions or simplify data entry into the database without thinking about formats and structure beforehand.

BASE Databases

While ACID databases are mostly RDBMS, most other database types, known as NoSQL databases, tend more to conform to BASE principles. Redis, CouchDB, MongoDB, Cosmos DB, Cassandra, ElasticSearch, Neo4J, OrientDB or ArangoDB are just some popular examples. But other than ACID, BASE is not a strict approach. Some NoSQL databases apply at least partly to ACID rules or provide optional functions to get almost or even full ACID compatibility. These databases provide different level of freedom which can be useful for the Staging Layer in Data Warehouses or as a Data Lake, but they are not the recommended choice for applications which need data environments guaranteeing strict consistency.

Benjamin Aunkofer

Data Warehousing Basiscs

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Data Warehousing is applied Big Data Management and a key success factor in almost every company. Without a data warehouse, no company today can control its processes and make the right decisions on a strategic level as there would be a lack of data transparency for all decision makers. Bigger comanies even have multiple data warehouses for different purposes.

In this series of articles I would like to explain what a data warehouse actually is and how it is set up. However, I would also like to explain basic topics regarding Data Engineering and concepts about databases and data flows.

To do this, we tick off the following points step by step:

 

Benjamin Aunkofer

Six properties of modern Business Intelligence

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Regardless of the industry in which you operate, you need information systems that evaluate your business data in order to provide you with a basis for decision-making. These systems are commonly referred to as so-called business intelligence (BI). In fact, most BI systems suffer from deficiencies that can be eliminated. In addition, modern BI can partially automate decisions and enable comprehensive analyzes with a high degree of flexibility in use.

Read this article in German:
“Sechs Eigenschaften einer modernen Business Intelligence“

Let us discuss the six characteristics that distinguish modern business intelligence, which mean taking technical tricks into account in detail, but always in the context of a great vision for your own company BI:

1. Uniform database of high quality

Every managing director certainly knows the situation that his managers do not agree on how many costs and revenues actually arise in detail and what the margins per category look like. And if they do, this information is often only available months too late.

Every company has to make hundreds or even thousands of decisions at the operational level every day, which can be made much more well-founded if there is good information and thus increase sales and save costs. However, there are many source systems from the company’s internal IT system landscape as well as other external data sources. The gathering and consolidation of information often takes up entire groups of employees and offers plenty of room for human error.

A system that provides at least the most relevant data for business management at the right time and in good quality in a trusted data zone as a single source of truth (SPOT). SPOT is the core of modern business intelligence.

In addition, other data on BI may also be made available which can be useful for qualified analysts and data scientists. For all decision-makers, the particularly trustworthy zone is the one through which all decision-makers across the company can synchronize.

2. Flexible use by different stakeholders

Even if all employees across the company should be able to access central, trustworthy data, with a clever architecture this does not exclude that each department receives its own views of this data. Many BI systems fail due to company-wide inacceptance because certain departments or technically defined employee groups are largely excluded from BI.

Modern BI systems enable views and the necessary data integration for all stakeholders in the company who rely on information and benefit equally from the SPOT approach.

3. Efficient ways to expand (time to market)

The core users of a BI system are particularly dissatisfied when the expansion or partial redesign of the information system requires too much of patience. Historically grown, incorrectly designed and not particularly adaptable BI systems often employ a whole team of IT staff and tickets with requests for change requests.

Good BI is a service for stakeholders with a short time to market. The correct design, selection of software and the implementation of data flows / models ensures significantly shorter development and implementation times for improvements and new features.

Furthermore, it is not only the technology that is decisive, but also the choice of organizational form, including the design of roles and responsibilities – from the technical system connection to data preparation, pre-analysis and support for the end users.

4. Integrated skills for Data Science and AI

Business intelligence and data science are often viewed and managed separately from each other. Firstly, because data scientists are often unmotivated to work with – from their point of view – boring data models and prepared data. On the other hand, because BI is usually already established as a traditional system in the company, despite the many problems that BI still has today.

Data science, often referred to as advanced analytics, deals with deep immersion in data using exploratory statistics and methods of data mining (unsupervised machine learning) as well as predictive analytics (supervised machine learning). Deep learning is a sub-area of ​​machine learning and is used for data mining or predictive analytics. Machine learning is a sub-area of ​​artificial intelligence (AI).

In the future, BI and data science or AI will continue to grow together, because at the latest after going live, the prediction models flow back into business intelligence. BI will probably develop into ABI (Artificial Business Intelligence). However, many companies are already using data mining and predictive analytics in the company, using uniform or different platforms with or without BI integration.

Modern BI systems also offer data scientists a platform to access high-quality and more granular raw data.

5. Sufficiently high performance

Most readers of these six points will probably have had experience with slow BI before. It takes several minutes to load a daily report to be used in many classic BI systems. If loading a dashboard can be combined with a little coffee break, it may still be acceptable for certain reports from time to time. At the latest, however, with frequent use, long loading times and unreliable reports are no longer acceptable.

One reason for poor performance is the hardware, which can be almost linearly scaled to higher data volumes and more analysis complexity using cloud systems. The use of cloud also enables the modular separation of storage and computing power from data and applications and is therefore generally recommended, but not necessarily the right choice for all companies.

In fact, performance is not only dependent on the hardware, the right choice of software and the right choice of design for data models and data flows also play a crucial role. Because while hardware can be changed or upgraded relatively easily, changing the architecture is associated with much more effort and BI competence. Unsuitable data models or data flows will certainly bring the latest hardware to its knees in its maximum configuration.

6. Cost-effective use and conclusion

Professional cloud systems that can be used for BI systems offer total cost calculators, such as Microsoft Azure, Amazon Web Services and Google Cloud. With these computers – with instruction from an experienced BI expert – not only can costs for the use of hardware be estimated, but ideas for cost optimization can also be calculated. Nevertheless, the cloud is still not the right solution for every company and classic calculations for on-premise solutions are necessary.

Incidentally, cost efficiency can also be increased with a good selection of the right software. Because proprietary solutions are tied to different license models and can only be compared using application scenarios. Apart from that, there are also good open source solutions that can be used largely free of charge and can be used for many applications without compromises.

However, it is wrong to assess the cost of a BI only according to its hardware and software costs. A significant part of cost efficiency is complementary to the aspects for the performance of the BI system, because suboptimal architectures work wastefully and require more expensive hardware than neatly coordinated architectures. The production of the central data supply in adequate quality can save many unnecessary processes of data preparation and many flexible analysis options also make redundant systems unnecessary and lead to indirect savings.

In any case, a BI for companies with many operational processes is always cheaper than no BI. However, if you take a closer look with BI expertise, cost efficiency is often possible.