apache/druid · critical · RE

Failed to find the DB Driver

Error message

Failed to find the DB Driver

What it means

After driver resolution, createConnectionFactory asserts that a Driver was actually obtained; if driverToUse is still null it throws RuntimeException('Failed to find the DB Driver'). This is an internal fallback indicating neither DriverManager resolution nor reflective instantiation produced a usable driver.

Source

Thrown at server/src/main/java/org/apache/druid/metadata/BasicDataSourceExt.java:165

          // respect the ContextClassLoader
          // N.B. This cast may cause ClassCastException which is handled below
          driverToUse = (Driver) driverFromCCL.newInstance();
          if (!driverToUse.acceptsURL(getUrl())) {
            throw new SQLException("No suitable driver", "08001");
          }
        }
      }
      catch (Exception t) {
        String message = "Cannot create JDBC driver of class '" +
                         (getDriverClassName() != null ? getDriverClassName() : "") +
                         "' for connect URL '" + getUrl() + "'";
        LOGGER.error(t, message);
        throw new SQLException(message, t);
      }
    }

    if (driverToUse == null) {
      throw new RE("Failed to find the DB Driver");
    }

    final Driver finalDriverToUse = driverToUse;

    return () -> {
      String user = connectorConfig.getUser();
      if (user != null) {
        connectionProperties.put("user", user);
      } else {
        log("DBCP DataSource configured without a 'username'");
      }

      // Note: This is the main point of this class where we are getting fresh password before setting up
      // every new connection.
      String password = connectorConfig.getPassword();
      if (password != null) {
        connectionProperties.put("password", password);
      } else {

View on GitHub (pinned to 9b90983fd2)

Solutions

1. Configure druid.metadata.storage.connector.driverClassName explicitly so the reflective path resolves the driver
2. Ensure the JDBC URL is valid and its driver is on the classpath
3. Inspect connector config construction so getDriverClassName()/getUrl() return real values

Example fix

// before
druid.metadata.storage.connector.connectURI=jdbc:postgresql://localhost:5432/druid
// (no driverClassName set)
// after
druid.metadata.storage.connector.connectURI=jdbc:postgresql://localhost:5432/druid
druid.metadata.storage.connector.driverClassName=org.postgresql.Driver

if (driverClassName == null || driverClassName.isEmpty()) { throw new IllegalArgumentException("driverClassName must be configured"); }

When it happens

Trigger: createConnectionFactory completing both driver-resolution paths without assigning driverToUse — e.g. no driverClassName configured and DriverManager.getDriver(getUrl()) did not throw but also no driver was captured, or unusual config combinations that bypass both branches.

Common situations: Incomplete metadata storage connector config missing both driverClassName and a resolvable URL; misconfigured custom connector config object where getters return null unexpectedly.

Understand the failure class

Background: "is required", "must be set", "missing required field": configuration validation errors across open-source libraries — this error's family across 36 libraries.

Related errors

• 08001
• Cannot create JDBC driver of class '<driverClassName>' for c
• Failed to parse metric dimensions and types
• JDBC driver JAR files missing from extensions/druid-lookups-
• JDBC driver JAR files missing in the classpath

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/78d592816850c698. Report an issue: GitHub.