Top 25 PostgreSQL Interview Questions and Answers in 2021


PostgreSQL Interview Questions and Answers

In this article, we take a look at some of the most common questions in PostgreSQL Interviews for beginners, intermediate and experienced job seekers to ensure that you have the upper hand in your interview and come off as experienced.

Therefore, take your time and go through our carefully crafted answers and think of unique responses where applicable. We will cover only 25 questions, but that does not mean that they are the only ones that you will be asked. Therefore, take some time and think about some additional questions that may pop up during your interview.

Let’s take a look at these:

1.    What Are Some of the Useful Features That PostgreSQL possesses?

PostgreSQL has several features that users find helpful. It allows users to build a fault-tolerant environment, thanks to its data integrity protection. It supports multi-version concurrency control and has high availability standby server.

It also supports the client-server network architecture and has a trigger and log-based replication SSL. Lastly, it is easily compatible with several platforms, languages and middleware.

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2.      In Your Experience, What Do You Consider Some of The Disadvantages of PostgreSQL?

Even though it is fully featured and compares well to a range of DBMS systems, PostgreSQL is still less famous since it is not owned by one organization. It is also slower than MYSQL when it comes to performance metrics.

Also, it is not as flexible as MySQL since it mainly focuses on compatibility and not changes for speed improvement. Lastly, several open-source apps that support its counterparts, such as MySQL, may not work with it, which is a huge disadvantage.

3.      When Would You Convince Someone To use PostgreSQL?

This open-source database comes in handy in many applications. It is fully ACID compliant and supports multi-version concurrency control. It, therefore, comes in handy when data integrity is critical. I would advise one to use it in projects that need integration with other tools as it is compatible with lots of programming languages and platforms.

The last instance is in complex operations as it supports query plans and uses several CPUs to answer queries faster.

4.      What Do You Understand by Sequence and Connector Libraries In Regards To PostgreSQL?

The sequence can be defined as a user-defined and schema-bound object that comes in handy in generating a sequence of integers. It can be built through a “CREATE SEQUENCE” statement. On the other hand, Connector libraries are a series of connectors that are easily downloaded and customized using any ProcessMaker, which manages and updates the connector public library.



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5.      What Are Some of The Instances Where One Should avoid PostgreSQL?

This open-source database system was mainly designed to be extensible and compatible. It does not, therefore, come in handy where speed is needed. It also has an extensive feature set and strongly adheres to standard SQL, making it a wrong choice in simple setups.

It does not also come in handy for complex replications, as MySQL does a better job.

6.      What Are Some of The Proven Advantages of PostgreSQL?

This database management system has its fair share of advantages. One does not have to train too hard when learning it as it is relatively easy to use. It further supports geographic objects and can be converted into a geospatial data store.

PostgreSQL has low administration costs be it for embedded or enterprise usage. Its source code is freely available through the open-source license, which enhances its ability to be used, modified or implemented based on the business needs.

7.      Can You Confirm That This DBMS Runs on The Cloud Like Other Existing Types?

Yes. It runs on the cloud, just like other open-source databases. It can be efficiently run in virtual containers, given its portability. It is also supported by several companies such as Heroku, Joyent and GoGrid when it comes to cloud hosting environments.

8.      Does This Open Database Have Possess Stored Procedures?

No. Not directly. It does not have a defined stored procedure as most database management systems. As opposed to other databases, PostgreSQL’s stored procedures are defined as FUNCTIONS and triggers. Therefore, this is usually a complicated feature depending on the return type.

 Even though these functions vary in features, they are all equal.

9.      How Can You Check Rows That Are Affected in The Previous Part of The Transaction in PostgreSQL?

Usually, the SQL standard is defined by four levels of transaction isolation based on three phenomena, which must be avoided between concurrent transactions. These will help check affected rows in the previous part of the transaction. They include the dirty reads, non-repeatable read and the phantom read. (You can further explain what these are. Just make sure that you get them right and relate them to the question)

10. What Do You Understand by Indexes in PostgreSQL?

Out of the means of performance enhancement in PostgreSQL, the index is one of the most common. This aids in the faster retrieval of specific rows by the data server. Well, this can happen without the index, just that it will be prolonged.

These must be implemented well as they also add costs to the database system. (an index can be easily defined as a pointer to specific data in a table. However, the more you appear knowledgeable, the more you boot your chances of landing the job)

11. What Do You Understand by Multi-Version Concurrency Control in PostgreSQL?

Also known as MVCC, this is an advanced method in PostgreSQL that improves the performance of the database in an environment of multiple users by fastening it. This makes PostgreSQL different from other databases since the locks acquired for data reading do not conflict with those obtained for data writing.

Multi-Version Concurrency Control, therefore, makes the process more compartmentalized and faster for improved performance, which makes it one of the most valuable features in this database.

12. What Do You Understand by Ctid and pgadmin is PostgreSQL?

The ctid is a field found in any PostgreSQL table. As common as it is, it is pretty unique for the records in these tables and shows the location of the tuple, which makes it applicable in the deletion of records. Users are advised to use only one ctid in situations where no other unique identifier exists.

pgadmin, on the other hand, is available under free software and forms a graphical front-end administration tool. It is released under artistic license to be used as an administration tool.

13. In Your Experience. What Do You Consider Some of The Advantages of Multi-version Control?

Multi-version concurrency control comes in handy when one wants to avoid unwarranted locking of a database. It removes the time lag (which occurs when another party is accessing given content), allowing the user to log into his/ her database.

This feature also keeps a record of all transactions.

14. What Do You Understand by Full Test Search, and Is It Supported by This Database?

Full-text search is a technique that allows users to locate a single or collection of computer-stored documents in full-text databases. This is normally different from regular searches as it is differentiated based on the metadata or parts found in the database.

It is available in PostgreSQL, but only as a feature. Other databases such as Elasticsearch and SOLR have excellent full-text search tools for more advanced usage or application.

15. Differentiate GiST and BRIN indexes in PostgreSQL

GiST exists as an extendable data structure where users can create indices to manipulate any data. It further supports lookup on the data by inserting an API to the index system of PostgreSQL.

On the other hand, BRIN empowers PostgreSQL to pick maximum and minimum values by reading the selected column for every 8K page of stored data. PostgreSQL will then store these values and the page number for the chosen columns in these indices.

16. Could You Please Explain What Functions Are in PostgreSQL?

These are some of the critical parts of PostgreSQL as they are needed to execute the code on the server. Functions can be programmed using several languages such as PL/pgSQL, several scripting languages such as Perl, Python and PHP, and a native PostgreSQL language. To increase their efficiency, one can use a statistical language, namely PL/R.

17. Could You Please Tell Us Some of The Functionalities of PostgreSQL?

There are five functionalities of PostgreSQL. These are object rational database, client-server and WAL, Extensibility and SQL support, DB validation and a flexible application program interface, and Procedural languages and Multi-Version Concurrency Control.

18. How Can One Perform Queries Using Multiple Databases?

It is impossible to query a database other than the existing database. PostgreSQL has database specific system catalogues, which makes it impossible to determine how a cross-database query will fair in regards to Postgres.

However, cross-database queries can be made possible using contrib or dblink with the help of function calls. It is also possible for a client to establish simultaneous connections to various databases and combine the acquired results on his/ her side. This, in fact, is the most familiar ways of performing multiple databases.

19. Can One Create a Shared Storage PostgreSQL Server Cluster?

There are several diverse clustering tools that one can leverage, given that no single type of clustering can meet all clustering needs. These tools offer user different clustering approaches and include open-source projects PostgresXC and Postgres-XL, open-source forks and proprietary tools. Some of the commonest include Greenplum Database and Citus Data.

This database is also supported by filesystem-based clustering systems. These are meant for failover and can be obtained from Red Hat, Microsoft, Oracle and Veritas.

20. What Do You Understand by The Triggers?

An SQL query allows you to trigger an event. These triggers are generally initiated through INSERT and UPDATE queries which you can attach to the tables. You can activate multiple triggers alphabetically. These also have the capacity to invoke commands or functions from other languages, which makes PostgreSQL a darling among many.

21. What Do You Know About String Constants, Given Your Time Dealing with PostgreSQL?

String constants have a sequence of characters, usually bound by single quotes. It is normally used when inserting a character or passing it to database objects. You can use single quotes with PostgreSQL even though you have to use a C style backlash.

22. From Your Experience, Could You Please Tell Us Some of The Enhancements to The Straights Relational Data Model by This Database? Also, Mention The Data Types Used in PostgreSQL

PostgreSQL provides a range of enhancements to its straight relational data model. These include multiple values, functions, inheritance and extensibility. Tables are generally referred to as classes. As for the data types, PostgreSQL supports Boolean, JSON, hstore, array, temporal, numeric, and character. Array consists of array string and number; temporal consists of date, time, timestamp and interval, whereas numeric entails the integer and floating-point. Lastly, character is made up of char, text and varchar.

23. How Can One Update Stats in PostgreSQL?

You have to make an explicit vacuum cell to update statistics in PostgreSQL. This is arrived at through a definite method, and only vacuum with the option Analyze is used. Its syntax is VACUUM ANALYZE.

24. What is a CTID?

A CTID identifies the specific physical rows by their blocks. They also offset positions within a table. These are usually used by index entries to identify the physical rows. However, this cannot be used as a long-term row identifier as the logical row’s CTID changes with every update.

 However, if not competing update is expected, you can freely identify a row within the transaction.

25. What Does the Error Memory Exhausted in Allocsetalloc()?

This error means that you have run out of virtual memory on your system or the kernel has a low limit for given resources.

Conclusion

These 25 questions sum up some of the commonest interview questions relating to PostgreSQL. Ensure that you have a good grasp of the subjects we have touched on before showing up for a related interview.

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