Hire the Top 3% of Freelance PostgreSQL Developers

The Expanding Demand for PostgreSQL Developers

The database management systems (DBMS) market is booming—it approached $80 billion in 2021, following a trend of consistent growth over the five preceding years. PostgreSQL, also known as Postgres, is a top choice for database management and is the preferred database technology among professional developers. As the DBMS market expands, the need for PostgreSQL engineers continues to increase.

Hiring PostgreSQL developers is not always straightforward: While other SQL engineers do have some skill overlap with PostgreSQL developers, only experienced PostgreSQL specialists know how to leverage PostgreSQL’s advanced features and how to be effective at performance tuning.

In this hiring guide, we outline the critical components of a PostgreSQL job description, interview questions, and assessments. We also define the difference between PostgreSQL and SQL developers from a hiring perspective and the complementary technical skills your role might require.

What attributes distinguish quality PostgreSQL Developers from others?

When looking to hire a PostgreSQL developer, it’s important to understand how PostgreSQL developers stand out in a broader context of database expertise (i.e., PostgreSQL versus SQL versus NoSQL skills). There are two basic types of databases:

• Relational (RDBMS) or SQL databases use tables with rows and columns, which is ideal for structured data; these databases facilitate complex queries and help developers enforce data consistency. Examples include PostgreSQL, MySQL, and Microsoft (MS) SQL Server.
  • With all of them, developers use Structured Query Language (SQL) to create and find data—but PostgreSQL extends the language with advanced features and customizations.
• Nonrelational or NoSQL databases use ad hoc, JSON-formatted “documents,” allowing for maximum flexibility amid changing requirements.

While most candidates should be savvy with relational databases, the best PostgreSQL developers will also identify which advanced PostgreSQL features are a good fit for your assignment.

You should require a high-level understanding of standard features and functionalities, such as:

To gauge a candidate’s depth of knowledge, ask them about specific PostgreSQL abilities and limitations, using its feature matrix for reference.

How can you identify the ideal PostgreSQL Developer for you?

Unless you are hiring junior-level engineers and have the flexibility for additional onboarding and training time, you should focus your efforts on finding developers with significant hands-on experience with PostgreSQL. When reviewing résumés, be wary of candidates who list only experience with SQL: SQL generalists will likely need to unlearn some habits specific to other SQL systems lest they risk implementing antipatterns that may cost your company—even before your app scales.

Ideally, candidates will have plenty of experience with the PostgreSQL subfeatures that are crucial to your project (e.g., JSON datatypes and functions for an app using a hybrid table/document architecture).

The mastery of PostgreSQL requires several complementary skills, but not all of them may be relevant to a given project.

Procedural languages allow PostgreSQL developers to reuse SQL-related code from directly within the database for performance and data consistency. There are four procedural languages in PostgreSQL’s core distribution:

• PL/pgSQL (similar to PL/SQL)
• PL/Python
• PL/Perl
• PL/Tcl

If your project already relies heavily on one or more of these, you may need to hire a developer with Python, Perl, or Tcl skills. However, that list has little to do with how developers interface with PostgreSQL from an app’s code. For example, if your app (or its back end) is written in Java, a Java developer will use PostgreSQL’s client libraries to run queries; a PostgreSQL developer can collaborate with them better if they also know Java, depending on team size and role overlap.

Certain database projects may also benefit from JSON-proficient developers. As mentioned, PostgreSQL is primarily a relational database, but PostgreSQL engineers can still harness the power of NoSQL functionality. Look to hire someone with strong JSON SQL experience and mastery of JSON datatype operators if you are considering a combined document/relational database model.

Finally, in rare cases, familiarity with C-family languages (C or C++) may be needed when hiring developers so they can create and maintain custom PostgreSQL extensions. However, many extensions exist as open-source projects and can be leveraged as is without C or C++ skills.

How to Write a PostgreSQL Job Description for Your Project

The next step in hiring a PostgreSQL developer is to customize role requirements based on your data and specific needs:

Regardless of their level of expertise in PostgreSQL, a solid candidate should have sufficient experience with databases and advanced knowledge of the SQL syntax as a foundation for additional PostgreSQL skills.

What are the most important PostgreSQL interview questions?

Effective interview questions are a critical piece in the hiring puzzle—and your ticket to top developers. You might ask standard SQL interview questions on topics like JOIN clauses and subqueries or more advanced questions on topics like window functions, CTEs, and recursive queries. The best interviews tailor questions based on project-specific factors.

After standard SQL questions, continue with more specific PostgreSQL interview questions, such as:

How would you handle deploying a database model change (e.g., an important column rename) with minimal downtime?

PostgreSQL supports transactional DDL, but even renaming a column can block a full table for reads and writes. This can cause downtime and deadlocks at the database level and may need nontrivial synchronization when deploying new application code that can work with both versions of the table. Splitting a model change into multiple steps that are safe to run at any time is the correct approach. Example action items might include:

• Notifying key stakeholders that production deployment may include possible downtime.
• Creating a backup copy of the table for later restoration, if required (i.e., when performing structural changes or bulk data updates in an important table).
• Running the column rename and subsequent possible data manipulation in the column.
• Committing changes (or rolling them back if unexpected issues occur).
• Verifying with stakeholders that the application works as expected after finishing deployment.

You should also test each candidate’s understanding of complex PostgreSQL features that are relevant to your project. For example:

When would you consider using a partial index?

Partial indexes are suitable for tables and queries in cases in which you are interested only in a subset of the data. A good example is indexing a status column that filters out most rows. This case might occur in the real world for a table that contains processed and unprocessed job data, where a business is only interested in quickly fetching unprocessed data using the status column.

When would you use table partitioning?

When large amounts of data are stored in databases, performance and scaling suffer. Partitioning helps by dividing big tables into smaller tables, which reduces memory swap problems and table scans. As a result, huge data sets become more accessible and manageable. Most of the operations on unpartitioned tables are applicable to partitioned ones.

Focusing on database administration tasks (e.g., optimization and monitoring) may also be useful when looking to hire seasoned PostgreSQL developers:

What are the key metrics in a PostgreSQL database, and which tools would you use to monitor them?

In terms of query performance, strategic logging is required for any nontrivial application. It is crucial to recognize long-running queries and optimize them (standard approaches include running EXPLAIN ANALYZE and checking query costs). On the application level, it is vital to have visibility into how many queries are issued for a single request to identify N+1 query problems. To handle scaling, it is a best practice to monitor the number of open connections and replication lags.

Services like Datadog and New Relic provide actionable insights regarding PostgreSQL performance and are easy to integrate into existing applications of various languages. pgAdmin is also an excellent open-source graphical tool for database administration; it can monitor database configuration and activity, track sessions and locks, catch long-running queries, and more, but much of this functionality can also be achieved by a PostgreSQL developer skilled with the psql command line.

What would you do if a client’s application (dependent on a database) is stuck and nonresponsive?

Cooperation with other application teams is crucial, as the root cause of the problem may be outside of the database layer (e.g., unresponsive application servers or network firewalls). If all other layers are functional, then engineers should use the performance optimization methods for debugging we’ve laid out here.

Finally, a case study approach may be useful while interviewing. The situation below assesses a candidate’s experience with at least one other relational database (e.g., MySQL, Oracle, MS SQL).

To determine each candidate’s ability to deal with real-world problems, ask them to create a relational database model that meets a set of business requirements that aligns with your project’s use cases.

Based on each candidate’s model, ask them:

• How would you query and manipulate data in the database?
• What trade-offs did you make in terms of performance, scalability, and maintenance?
• How would you run an EXPLAIN on a query? Please include a proposal to optimize the query plan.

All candidates should demonstrate a clear understanding of these relational database concepts.

While interviewing, consider other relevant developer strengths from the complementary technologies mentioned in the “How can you identify the ideal PostgreSQL Developer for you?” section, plus more general engineering topics:

• Dockerized and cloud technologies are prevalent in PostgreSQL application architectures. Ask candidates about their experience with cloud database configurations, including experience with dockerized environments (containers) and major cloud providers.
• No software engineering interview is complete without situational questions that assess problem-solving and debugging skills. These capabilities are essential for all developers, regardless of their technology or language specialization.

If you need support on high-level performance or architecture decisions, inquire directly about plans to assess your specific problem. Experts working at this level will have strong experience and referrals. They may suggest clear proposals for onboarding clients, defining the project’s next steps, and managing stakeholder expectations.

Why do companies hire PostgreSQL Developers?

PostgreSQL engineers can handle various data sets, whether serving small projects or global enterprises, and PostgreSQL is available for use with major cloud providers like Amazon Web Services, Microsoft Azure, and Google Cloud.

Common real-world use cases for PostgreSQL and other relational databases include transactional applications (e.g., customer relationship management systems) and other scenarios in which data does not change frequently (e.g., storing healthcare data, government data, electricity or mobile plan data, or financial data). An SQL generalist could be all that you need in such cases if there’s already enough PostgreSQL expertise on your team, but you’ll need a PostgreSQL specialist for your app to scale at an enterprise level.

PostgreSQL is an RDBMS first, but PostgreSQL developers can also harness the power of NoSQL functionality and work on projects with unstructured data using a combined document/relational data model. This approach is possible due to PostgreSQL’s rich JSON support, and it requires an engineer who has worked specifically with JSON datatypes in a production system.

While PostgreSQL is a versatile tool, it may not be suitable for every project. For example, other approaches offer better solutions when dealing with huge amounts of unstructured data or blob storage where you don’t need ACID compliance. But you still may benefit from PostgreSQL developers when using other technologies if you are migrating data from PostgreSQL.

As the DBMS market continues to grow, companies will increasingly look to expert PostgreSQL developers to harness the profits of large data sets and stay competitive. With the guidance offered here, you will be better prepared for every step of the hiring journey—from drafting your PostgreSQL job description to identifying the required advanced PostgreSQL skills for development. Zeroing in on the right PostgreSQL experts will drive your data—and your business—toward success.

The technical content presented in this article was reviewed by Tomislav Delas.