Fixing the PSQLException Relation Error in Spring Boot and Keycloak After PostgreSQL Migration

Common Challenges with Keycloak and PostgreSQL Migration

When migrating a Spring Boot application with Keycloak from MariaDB to PostgreSQL, developers often encounter unexpected issues related to database schema management. One such error is the "PSQLException: relation does not exist," which can cause significant frustration, especially when the table in question seems to be present.

This error typically surfaces when multiple connections or processes try to access Keycloak tables simultaneously, leading to confusion about PostgreSQL's handling of such interactions. It’s crucial to ensure that all components, including the database schema and table configurations, are properly aligned after migration.

In this case, the application can connect to the database, but errors still arise during runtime. Developers should be aware of PostgreSQL’s specific behavior with table access, schema handling, and its differences from MariaDB to diagnose and resolve these issues effectively.

By carefully verifying database credentials, schema presence, and PostgreSQL configurations, the underlying cause of the error can often be identified. This guide will explore potential solutions and troubleshooting steps to help resolve the "relation does not exist" error after migrating Keycloak and Spring Boot applications to PostgreSQL.

Understanding and Optimizing Solutions for PostgreSQL Relation Errors in Keycloak

In the provided scripts, the first solution revolves around verifying the existence of a table in PostgreSQL using a native query in Spring Boot. The command entityManager.createNativeQuery allows the execution of raw SQL, bypassing the traditional entity mapping system. This is particularly useful for troubleshooting schema issues like the one seen with the "relation does not exist" error. The query interacts directly with PostgreSQL’s system tables (specifically information_schema.tables) to check whether a required table, such as keycloak.user_entity, exists in the database schema. By binding parameters with query.setParameter, the solution ensures flexibility, allowing developers to test different tables dynamically.

The second script demonstrates how Flyway can be used to manage database migrations. By leveraging Flyway, you ensure that all database changes, including table creation and modification, are automated and versioned. The Flyway migration configuration ensures that the necessary schema is applied to PostgreSQL as soon as the application starts. For instance, the setting spring.flyway.baseline-on-migrate tells Flyway to baseline the schema if previous migrations exist, ensuring it doesn’t fail in production databases where tables like user_entity may already exist. This solution is ideal for avoiding manual schema inconsistencies during migrations between databases.

The third solution focuses on writing unit tests using JUnit to validate the presence of the schema. In the test, the command assertTrue is used to confirm that the table exists, ensuring schema validation occurs before the application tries to interact with it. This test provides a layer of security, ensuring the application's core functionality won’t fail due to missing database elements. By integrating such tests in the CI/CD pipeline, developers can proactively catch database issues like table misconfigurations before they cause runtime errors in production.

Each solution provided not only addresses the specific problem of schema verification but also emphasizes performance and security. The raw SQL query is optimized for direct table access, while Flyway ensures schema synchronization and migrations are automated. These solutions can be used in tandem, with Flyway managing schema updates and the native query or unit tests verifying table integrity post-migration. By combining these techniques, developers can robustly manage PostgreSQL databases within Spring Boot, ensuring smooth transitions from MariaDB while minimizing errors related to missing relations.

// Import necessary libraries
import javax.persistence.EntityManager;
import javax.persistence.Query;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

@Service
public class DatabaseService {
    @Autowired
    private EntityManager entityManager;

    // Method to verify the existence of a table
    @Transactional
    public boolean checkIfTableExists(String tableName) {
        try {
            String queryStr = "SELECT 1 FROM information_schema.tables WHERE table_schema = 'public' AND table_name = :tableName";
            Query query = entityManager.createNativeQuery(queryStr);
            query.setParameter("tableName", tableName);
            return !query.getResultList().isEmpty();
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }
}

// Add Flyway dependency in your pom.xml or build.gradle
// For Maven, include this in pom.xml
<dependency>
    <groupId>org.flywaydb</groupId>
    <artifactId>flyway-core</artifactId>
    <version>8.0.0</version>
</dependency>

// In application.properties or application.yml, configure Flyway
spring.flyway.enabled=true
spring.flyway.locations=classpath:db/migration
spring.flyway.baseline-on-migrate=true

// Create SQL migration file in the directory specified in Flyway
// For example: db/migration/V1__Create_keycloak_user_entity.sql
CREATE TABLE keycloak.user_entity (
    id UUID PRIMARY KEY,
    username VARCHAR(255) NOT 
);
// Flyway will automatically manage schema updates during application startup

// Import necessary testing libraries
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertTrue;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.transaction.annotation.Transactional;

@SpringBootTest
public class DatabaseServiceTest {
    @Autowired
    private DatabaseService databaseService;

    @Test
    @Transactional
    public void testTableExists() {
        boolean tableExists = databaseService.checkIfTableExists("user_entity");
        assertTrue(tableExists, "The table user_entity should exist in the schema.");
    }
}

Resolving Concurrent Access Issues in PostgreSQL with Keycloak

Another crucial aspect to consider when migrating from MariaDB to PostgreSQL is how PostgreSQL handles concurrent connections and table locking, especially with an application like Keycloak. PostgreSQL implements a multi-version concurrency control (MVCC) system, which means each process gets its own snapshot of the database. However, under certain circumstances, simultaneous access to the same table, particularly during transactions, can result in conflicts or errors if the schema is not optimized for such conditions.

One effective approach to avoid these issues is to review the transaction isolation levels and ensure they are correctly set. By default, PostgreSQL uses the “Read Committed” isolation level, but for applications that perform heavy, concurrent table access (like Keycloak’s user_entity table), developers might need to consider higher isolation levels like "Serializable." This can prevent conflicts but comes with the trade-off of potentially reduced performance. Optimizing database indices is also essential in ensuring efficient data retrieval and reducing contention.

Another aspect that is often overlooked is how the PostgreSQL database is configured to handle high volumes of concurrent requests. Tuning parameters such as max_connections and work_mem in the PostgreSQL configuration can drastically improve performance and reduce errors related to database connection limits. These adjustments ensure that Keycloak can manage user sessions and authentication without causing database bottlenecks or errors due to process collisions.