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Real DBA interview questions -2

Admin — Wed, 09 Mar 2022 09:04:55 +0000

Candidate has experience of 10 years in oracle dba and postgres. Below are the questions asked .

First round:

oracle dba question

What happens during hot backup?
Why hot backup generates lot of redo?
Different between small file tablespace and big file tablespace . Can pros and cons of both type of tablespace?
Cconfigure controlfile autobackup on- what is the use and is it mandatory?
Can I drop the controlfile of asm instance
How asm interacts with database
How I improve the i/o performance between asm and database instance
Different between expired and obsolete
What is partition pruning?
Can I restore a database from obsolete backup?
Difference between retention 7 days and recovery window 7 days
What it the role backgrond process LMON?
What is i/o fencing
How can u find the master nodes in oracle RAC
Between raw device and asm , whose performance is better
Can I have disks of different sizes in a diskgroup
What is the minimum number of diskgroups in rac and why ?
User is complaing that he is getting block sessoion in RAC, but when we checked by connecting to that instance, then you don’t see any blocking session. Even the sid is also not available, What could be the issue
What g stands in gv$sqll
Different paramters in Asm instance
What is hugepages and how it is related to RAC?
What is the default pagesize in linux
Where can you find the oratab entry in sun solaris.
Can I move the oratab entry to /etc/oratab
What is ACMS?
Are you aware of hangcheck?
How comfortable you are with shell scripting?
Yesterday RMAN backup ran for 10 min , But today it is taking more than 1 hour and it is still running. Note – databaese size is same, And load is normal.
Do you know what is hangcheck timer
What is load balancing advisory?

Postgres question:

What is ctid in postgres
I want to rebuild all the indexes in postgres, How can I do?
How can we reset the password in postgres?
How can u check the version in postgres
Explain datatypes in postgres
What type of querying language postgres support?
What is the latest postgres version. And which postgres version currently you are using?
Which tools you use to manager and monitor postgres
Compare postgres and oracle
While dropping a database in postgres, I am getting error and unable to drop. What could be the issue?

2nd round:

Candiate didn’t receive any confirmation regarding the 2nd round of techno-managerial interview. Most likely candidate got rejected by the panel in the 1st round.

NOTE – > Some of the answers you can find in our interview qa section.

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Real Interview questions for experienced DBAs – 1

Admin — Mon, 10 Jan 2022 15:19:44 +0000

Overview:

Below are the questions asked to a candidate with 10 years of experience in Oracle DBA and postgres . There were 2 rounds.

Round 1 :

What are your day to day activities. And what is your role in the Team?
Explain cluster startup sequence.
Suppose users are connected to node1 and Os team, want to do emergency maintenance and they need to reboot. What wil happens to the transactions on node1 , and can we move them to node 2.
What are the advantages of partitioning?
Can we convert non-partitioned table to partitioned table online( in production)?
What are the cloning methods. And what is the difference between duplicate method and restore method?
How can we open the standby database as read write for testing and Once testing is done need to revert to previous position. But without using snapshot command?
Explain how you did grid upgrade.
Which advanced security features you have used ?
What is audit purging?
Lets says a query was running fine for last few days , but today it is not performing well. How you will troubleshoot it?
What is oracle in memory ?
Explain what type of patches you applied on grid.
As per resume ,You have worked on ansible . So how good you are with ansible and what type of scripts you have wrote.
How can you troubleshoot a shell script?

2nd round:

Explain ASM architecture , means when ever user runs a query, how it gets the data from ASM.
Why ASM performance is better
Why VIP is used , Bcoz before 10g vip was not used. What benefits vip provide
What is Current block and CR block in RAC
What wait events are there in RAC??
What is gc buffer busy wait
What is gc 2 way current wait, gc 3 way current wait.
What is node eviction. In which cases it happens.
How you do load balancing using services in your project. Explain
What activities you did using goldengate
How you did upgrade/migration using goldengate.
What is goldengate instantiation.
What is bounded recovery in goldengate
What is the difference between CSN in goldengate vs SCN in database?
Which type of os tool/commands you have used for os monitoring/performance. And how you read it.
How you troubleshoot I/O issues in oracle
What type of sql performane tools you use.
How you migrate a plan from one db to another db
What is the dbms package for baseline and sql tuning?
Lets say, despite importing the baseline, query is not picking the plan, What can the be reason?
What is index fast full scan and index range scan?
What is the purpose of standby redolog.
Any automation tools you have used?
Did you worked on jenkins or gitlab?
What activities you did in postgres.
How you implement backup in postgres.
Is your postgres cluster active active or active passive?
Can we create a active active postgres cluster?
Do you remember any postgres extensions?
What type of scripts you have written on ansible?
Tell me some modules of ansible.
How can we encrypt the server credentials in ansible.

If you wish to share your interview experiences, then please drop a mail to support@dbaclass.com. We will happy to publish it with your permission.

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How to Choose the Right Mobile App Database for Your App

Harikrishna Kundariya — Tue, 24 Aug 2021 14:31:46 +0000

Have you ever wondered what is one of the most challenging tasks for mobile app developers? Well, it is to be able to choose the right app database. The mobile app market is full of a myriad of options and that’s what makes it critical for developers to choose the right app database. Without the right database, it would be difficult to develop and update the mobile app.

In general, databases are places that are used for storing data that can be retrieved later. A database also plays an important role in managing the data stored and helps to get rid of security issues.

Therefore, let’s look at what app databases are and how to choose the right mobile app database for building your mobile app.

What are app databases?

Data is stored as rows and columns in databases. Databases are collections of structured information kept in an organized manner as per the requirements of the application. Databases are modified, managed, and updated with the help of database management systems (DBMS). Databases are electronically stored on a PC and most developers take the help of the Structured Query Language to structure app databases.

Advantages of using a mobile app database

A mobile app database offers various benefits:

Helps to manage massive amounts of data.
App databases provide high data security.
DBMS offers DML, which is known as Data Manipulation Languages. This helps to update the app database easily.
Data Query Languages helps to search through app databases quickly.
App databases reduce data management costs.
DBMS is highly dependable and reduces errors and improves data consistency.

Popular mobile app databases in 2021

Some of the most popular databases used by Android & iOS app developers in 2021 for Mobile Apps are:

MySQL: MySQL is an open-source, multi-threaded SQL database.

PostgreSQL: Written in C language, PostgreSQL is an open-source, object-based, relational database.

SQLite: It is an embedded database used to provide local data storage ability to mobile apps.

MariaDB: This is another open-source relational database.

MongoDB: It is a document-oriented database that uses JSON and is known to offer a lot of flexibility.

Cassandra: This is a NoSQL database that can handle a large amount of unstructured data.

Realm DB: Realm DB is a relational DBMS that works like a conventional database storing data efficiently.

Types of mobile app databases

There are different types of databases for mobile apps that have been elaborated further to understand what type of database you should go with as per your requirement.

Centralized Database – A centralized database stores, locates, and maintains data in one location on a central computer.

Distributed Database – A distributed database consists of a sum of the data stored in common databases along with the information stored on each device.

Cloud Database – This database stores data in the cloud that can be accessed from anywhere and anytime.

Commercial Database – Enterprise-based database apps which are used to store employee information rely on such commercial databases.

End-User Database – Apps that deal with end-user data store such information in the end-user database.

NoSQL Database – This database functions differently compared to all other databases. It has a flexible schema that allows it to store data in numerous shapes and sizes instead of rows and columns.

Relational Database – Apps that are constantly using relational data need relational databases.

How to choose the right app database?

Different mobile apps might have different kinds of requirements. Hence it becomes crucial for the developer to choose the right kind of database for the app for its optimal function.

Below are some of the factors to consider that can serve as a guide as to which database a developer should choose.

Data Structure

The data structure refers to how data has to be stored and retrieved. There are several data formats for mobile apps and hence picking the database as per the data structure is essential.

If your app is to mainly function online, then data can be stored on servers and cloud whereas if it has to function offline, then data can be stored on the smartphone.

Data Size

If you are already aware that the app you are developing has to deal with a large amount of data, then it is recommended to go with a database that can handle huge amounts of data.

The type of data and the data structure affects the amount of data that a database can handle efficiently. Different databases offer a different capacity of data storage, so considering the limitations of every database is essential before deciding to go with one particular database. Overall, if the database has to deal with large amounts of data from different locations, then you can go with multiple databases.

Data Modelling

Data Modelling is the representation of the data structures that would be stored in the databases. Data Modelling is useful where the app has to offer a search function, location-based features, etc. Such apps can use multiple databases to support the wide array of features and handle data sizes from different locations.

Data Security

Mobile app databases are responsible for storing huge amounts of sensitive data. Databases are often susceptible to malware attacks. Therefore, security is another crucial point that needs to be considered when choosing a database. A database that offers an integrated authentication system and the use of third-party security service providers is the best choice to go with.

Speed & Scalability

When it comes to the speed and scalability of a database, then, on one hand, some databases would be capable of supporting read-heavy apps, whereas, on the other hand, some apps would be ready to support write-heavy solutions.

So, choosing a database that can optimize both reads and writes functions on your app is needed for apps that have to address such solutions.

Cross-Platform Support

If an app is meant to function on multiple platforms, then choosing a database that supports cross-platform development is essential. Such a database would help make the app scalable, adaptable, and expandable.

Conclusion

So, here is a complete roundabout on how to choose the right mobile app database while developing a new mobile app or while adding new features to an existing app. You can choose a database as per your requirement. The most popular databases in 2021 are MySQL, PostgreSQL, SQLite, MongoDB, MariaDB, Cassandra, Memcached, etc.

The post How to Choose the Right Mobile App Database for Your App appeared first on DBACLASS.

Oracle Data Guard vs. Oracle GoldenGate

Admin — Thu, 12 Aug 2021 12:50:36 +0000

Oracle Data Guard and Oracle GoldenGate are disaster recovery software used for data replication. The two software are mainly the top picks for disaster recovery. Other software like Dbvisit (https://dbvisit.com/ ) might also be a preference for most people. But in this article, we’ll compare the two popular data replication technologies.

Oracle Data Guard

Oracle Data Guard is one of the best data protection software out there for the oracle database. It works in a very simple manner by maintaining an exact physical replica of the production copy remotely. Oracle Data Guard works without any issue and performs active-passive data replication for high availability of data.

In Oracle Data Guard, data replication can happen only on homogenous data platforms that use identical database management systems (DBMS) and operating systems. Such systems are a network of two or more Oracle databases residing in one or more machines. The Data Guard completes one-way physical replication and these replications can be configured only between oracle to oracle.

The Oracle Data Guard uses Active Data Guard, known for its simplicity, data availability, best data protection, and high performance. As a result, it passes for the simplest and the fastest one-way replication of a complete Oracle database. Unlike GoldenGate, Data Guard is very simple to use and supports all applications and workloads. It has no data type restrictions and it’s very transparent to operate. There are no requirements for supplemental logging. Also, there are no performance implications for tables without a unique index or primary key with Data Guard. In addition, the need for performance tuning is also zero to none at the standby database.

Oracle Golden Gate

Oracle GoldenGate is more of an advanced logical replication product, which supports very flexible options for data replication, including multi-master replication, hub and spoke deployment, and data transformation. It runs with logical replication of the database that includes Active-Active HA, one to many, many to one, subset replication, and transformation. Data replication can only happen in heterogeneous data platforms where the database is distributed among dissimilar sites that run under different DBMSs.

Oracle GoldenGate is used mainly when a replica database needs to be open read-write. At the same time, replication is still active for advanced replications requirements that Active Data Guard can handle. In data replication, the GoldenGate supports Multimaster and bidirectional replication instead of one-way data replication.

The Oracle Goldengate is not the simplest software to use, but it offers rich functionality, flexibility, and additional deployment considerations. But one of its downsides is the lack of support for data types like XML and BLOB. You also don’t get transparency of backup and only replicated data are similar to each other.

Unlike the minimum downtime in Data Guard, you have zero downtime for maintenance and migrations in GoldenGate, but you need to configure a bi-directional replication. In Oracle GoldenGate, a minimum supplemental log should be enabled. You might also face some performance issues if the table doesn’t have any primary key.

Oracle Data Guard and GoldenGate are almost two opposite options for data replication. One is a simple option, while the other passes for an advanced data replication option. For people looking for software somewhere between simple and advanced, other software like Dbvisit are also available. With Dbvisit, you get a 10-day trial or a demo to let you decide which disaster recovery solution fits you the best.

Author – Zachary Danielson

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Automation Testing in CI/CD

K SRI — Sat, 28 Nov 2020 07:17:02 +0000

Automation testing focuses on continuous testing to identify bugs and defects early in the software development life cycle. It does this by using the tools that give priority to quality. One of the most persuasive features of the CI/CD pipeline is the scope to test the software code more frequently without overburdening the operators or developers with the manual work. In this article, we look at why automation testing is essential to the CI/CD pipeline.

What is Automation Testing

Automation testing is the implementation of the software tools for automating the human-driven manual process of validating and evaluating a software product. Nowadays, almost every software project includes automation testing from the starting phase of the SDLC. Automation testing brings massive benefits for team effectiveness and ROI of the quality assurance reams.

What are Continuous Delivery and Continuous Integration

Continuous Delivery

Continuous Delivery is also known as Continuous Deployment. Everything that is integrated by the software development team is continuously deployed to the real-time environment.

Continuous Integration

Continuous Integration is a process in which the developers integrate their code into a shared repository. This process helps maintain the quality of code and detect possible issues with the native version of the code at the starting stage.

Reasons for Implementing Automation in CI/CD Pipeline

Testing is an essential element of all release cycles. The integration of automation testing helps companies handle the challenges they face while delivering a quality software product. Unit testing, User Integration testing help in assuring that code meets the standard quality.

CI allows the software development teams to modify the code to fix the bugs and handle the business requirements, which get tested concurrently. At the same time, CD enables the users to obtain the new version of the software product at the earliest.

Following are the key factors that we should consider to use Automation testing in the CI/CD Pipeline.

1) Identifying Bugs at an early stage: One of the most significant advantages of automation testing is identifying the errors at an early stage of software development life cycle(SDLC). The bug found in the initial phase of SDLC needs fewer resources and costs to be dealt with, in comparison to the bug found in the later stages of the Software Development Life Cycle( SDLC).

2) Handling small changes: In the CI/CD Pipeline, almost every update and code integration is small. In comparison to Manual testing, Automation is more suitable to test those small updates. It reduces the manual testing tedium that takes place with the small updates and allows the testing team to continuously deliver a steady flow of small changes that have been completely tested.

3) Rapid Testing: Continuous Delivery needs rapid testing. Automation testing gives results much more rapidly than Manual testing. Simultaneous automation testing reduces the testing duration.

4) Consistency: An efficient CI/CD pipeline will have little abnormalities and deviations. Maintaining the process consistency assures that expectations are satisfied completely to release the product.

5) Agility: In a strong Pipeline, we must be able to adjust the frameworks, tools, and configurations as the new methodology becomes available. Working it out with manual testing makes it hard to be agile. It is useless when the team has to occasionally rewrite or reconfigure the test cases when the CI/CD pipeline requires an update. Through automation testing, we can do reconfiguration and rewrite automatically.
6) Product Quality: Executing automated parallel and regression tests will enhance test coverage, assuring your application is error-free and works throughout a broad range of environments.
7) Cost Reduction: Automated testing environment deploying will minimize the costs associated with maintaining your own testing infrastructure. Simultaneous(Parallel) testing will reduce the number of systems you require to execute your tests on.
8) Testing and Development go hand to hand: Automation testing optimizes the software delivery and makes the software development and testing team work together. It eases the coordination between the IT operations team and the development team.

Best Methods for the CI/CD Pipeline to get the best from the test automation

1) Progressive Changes: To implement automation testing, the CI/CD pipeline must adapt the feature-by-feature approach. When the feature is large, we can break it into smaller and quicker for testing the features. This approach is essential for automation testing because it is easy to identify the root cause if there is a problem.

2) Parallel Testing: In the CI/CD pipeline, we must execute the tests in parallel for making the tests effective and convenient. It minimizes the time taken for executing the tests, thereby produces the results much rapidly. But It is not enough to just run the tests parallely, it is also essential to scale the size of the server to make the tests run quicker.
3) Identifying what must be Automated: Generally, software testing teams dive fast, and they say, “Let us automate everything,” but this is a common blunder. First, we should know the objective of the automation and determine the test cases that we must automate.

What kind of tests must be automated

1) UnitTestingUnit testing covers the separate units of the code. We test the units of the code in the function definitions. Each unit test will handle a function. The unit testing tests the code that has essential computations. Unit tests are affordable, fast to implement, and gives a high ROI(Return-on-Investment). If the software testing team does not automate the unit tests, the probability of getting success is very little.
2) PerformanceTestingIn the context of software development, the “performance” term explains the responsiveness and speed at which the software project responds. Some performance measures are: “time for loading the page,” “search results response time.” Automated performance testing executes the test cases throughout these measures and, after that, alerts the software development team regarding any speed loss or regression.
3) Integrationtesting

Generally, a coding unit will do an external call to the extrinsic service. The main source code that we test will not have access to this extrinsic service. Integration testing will test these extrinsic dependencies and validates the accuracy of the software boundary. Integration testing is identical to unit testing in the way we develop it. It is an affordable alternative to the End-to-End testing,

4) APITesting

API testing tests the validity of the interoperability and logical layers among software systems and components. Instead of producing the mouse or keyboard input, API testing produces the calls to the API resources and checks the responses to those calls. The critical challenge to efficient API testing is the correct test environment setup; we can achieve it through more programming configuration and less visual interaction. This is one of the most complicated aspects of automation testing.

Conclusion

Automation testing is crucial in the successful deployment of software projects while maintaining standard quality. It assures that tests are run at every stage and provides good clarity on the code quality. Automation testing builds quality in the CI/CD pipeline and accelerates the software testing and deployment process.

Author Bio:

I’m Srija Kalavala a fascinated Technical Content writer currently working at Mindmajix. Interested to know about technology updates. I Can write an article on the following technologies Database Management, Cloud Computing, Business Intelligence and Analytics, Cyber Security and SIEM Tools, etc. Get connected with me on Linkedin.

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What is the Future Possibility of a Career in MS SQL Server?

sharafudhin Mangala — Wed, 03 Jun 2020 06:56:33 +0000

Ever before you are planning to start or change your career into one of the most popular database languages, MS SQL Server (Microsoft Structured Query Language), you need to know the future prospect of this language which is created to interact with a database. This blog will help you to know the future prospect of choosing a career in MS SQL Server.

What is SQL Server?

MS SQL is a software developed by Microsoft, which is a relational database management system (RDBMS) and also an Object-Relational Database Management System that supports a wide variety of transaction processing, analytics applications and business intelligence in corporate IT environments.

MS SQL is also a graphical user interface (GUI) and command based software. A GUI can display objects that convey information, and represent actions that can be taken by a user.

Where is MS SQL used?

MS SQL is used to create and maintain databases. Databases are part of every company with a website and SQL is used in every industry to deal with complex databases. Constant interaction happens in SQL which includes updating, deleting, and requesting information from the database. It is a relational web hosting database which is used to store website information like user information and blog posts. MS SQL is the most popular database type on Windows servers.

MS SQL is used to analyze the data through SQL Server Analysis Services (SSAS) and to generate reports through SQL Server Reporting Services (SSRS).

It can be used to carry out ETL (extract, transform, load data out of one database and place it into another database) operations through SQL Server Integration Services (SSIS). Although MS SQL is not a free language it has all the advanced features that make it suitable for businesses.

MS SQL Features

An MS SQL Server database is capable of storing any type of data you want. It will enable you to quickly store and retrieve information on servers. When multiple visitors come to your website they can use it at one time. The SQL statements you use help to accomplish all this. Speaking in technical terms, most MS SQL Server versions have the following features:

Full-text search service
Logging and Transaction
Concurrency and locking
Buffer management
Replication services
Notification services
Analysis services
Integration services
Stored procedures
Sub-SELECTs
Triggers
Views

Careers in SQL server

There are millions of SQL Server databases around the world on-premises and in the cloud such as Azure, Amazon Web Services etc. Careers in SQL Server are vast and have quite a lot of theories and concepts. If you’re an MS SQL aspirant who would like to make a career with SQL, then you should master all the important concepts and get a better understanding of creating queries. There are some of the most important skills that one aspirant needs to acquire before starting a career in SQL. Numerous technology professionals work with SQL Server on a daily basis.

Different Roles in MS SQL Server

There are different roles available in SQL Server and not everyone who works with SQL Server handles the same role. Anyone cannot really master everything the platform has to offer. There are database developers, DS or Data Scientist, Report writers, DBA or Database Administrator, and DA or Data Analyst, BI Admin or Business Intelligence Administrator and more other roles. Like any other technology jobs, these roles too fall high in terms of compensation.

Scope of MS SQL Career

Although there are numerous notable programming languages on the market, SQL is a specialized language rise in popularity in data-intensive fields like Big Data and machine learning. The demand for database technology is massive in the market as everything functions with the help of data. So, if you’re an aspirant, you must realize your strength and skills and act accordingly to choose a specific area of interest to be more productive in your career.

Now, you or the company you’re working have too many questions related to data such as previous year sales, average customer satisfaction rating, reduced expense rates of a certain period, all these can be answered using SQL.

Qualification to secure a career as a SQL Server Developer

Do you think you don’t have a technical background to get a job in the IT industry? Don’t underestimate yourself but understand the business aspect and propose the most creative solutions. If you know how to code and believe that you can perform and implement solutions, you can easily become a SQL Developer. It does not matter whether you belong to an IT or non-IT background, but getting certified in MS SQL Server will easily find you a job as a SQL Server Developer. You may earn certification by joining the online SQL classes and practice continuously for some time to become an expert. The thing you make yourself skilled and educate yourself to hit the right profile, it will help you to build a professional career as a MS SQL Developer.

To put more simply, SQL empowers you to answer your own questions. Therefore, you no longer have to rely on overly simplified, pre-built reports and emailing co-workers to track down data. SQL enables you to become a more self-sufficient employee in the IT industry.

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