pentaho/pentaho-kettle · error · KettleException

Truncate table is not supported!

Error message

Truncate table is not supported!

What it means

MonetDBBulkLoader.truncate builds its statement from the database meta's getTruncateTableStatement(). When that returns null — the configured dialect does not support TRUNCATE for this target — a KettleException is thrown. It protects the step from executing an invalid or fallback statement.

Solutions

  1. Verify the connection's database type is MonetDB (or a dialect implementing getTruncateTableStatement)
  2. If the dialect doesn't support truncate, disable truncate and run a separate Execute SQL DELETE step instead
  3. Upgrade PDI/database plugin versions so the dialect supports truncate statements
  4. Confirm the schemaTable name resolved correctly (bad table resolution can short-circuit statement generation)

Example fix

// before: truncate enabled on an unsupported-dialect connection
Truncate table = true   (connection: Generic DB)
// after
Truncate table = false; use an 'Execute SQL' step: DELETE FROM schema.table
Defensive patterns

Strategy: fallback

Validate before calling

// Detect truncate support before enabling the option
String stmt = meta.getDatabaseMeta().getTruncateTableStatement(null, "schema.table");
if (stmt == null) {
  System.out.println("Dialect " + meta.getDatabaseMeta().getPluginId()
      + " does not support TRUNCATE; disable truncate or use DELETE");
}

Type guard

null

Try / catch

try {
  step.run();
} catch (KettleException e) {
  if (e.getMessage().contains("Truncate table is not supported")) {
    logError("Switch to a DELETE-based clear step or fix the connection dialect");
  }
}

Prevention

When it happens

Trigger: execute() sees the truncate option enabled and calls truncate(); the configured DatabaseMeta dialect returns null from getTruncateTableStatement (unsupported dialect).

Common situations: Pointing the bulk loader connection at a non-MonetDB or unsupported database dialect; custom/modified connection type; older database plugin lacking truncate support for the dialect.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of pentaho/pentaho-kettle@f3058517a1 (2026-09-13). Data as JSON: /api/errors/f0130ee7cef49ed4. Report an issue: GitHub.

Appendix: source

Thrown at plugins/monet-db-bulk-loader/impl/src/main/java/org/pentaho/di/trans/steps/monetdbbulkloader/MonetDBBulkLoader.java:387

      //
      line.append( data.newline );

      // Now that we have the line, grab the content and store it in the buffer...
      //
      data.rowBuffer[data.bufferIndex] = line.toString(); // line.toByteArray();
      data.bufferIndex++;
    } catch ( Exception e ) {
      throw new KettleException( "Error serializing rows of data to the MonetDB API (MAPI).", e );
    }

  }

  public void truncate() throws KettleException {
    String cmd;
    String table = data.schemaTable;
    String truncateStatement = meta.getDatabaseMeta().getTruncateTableStatement( null, table );
    if ( truncateStatement == null ) {
      throw new KettleException( "Truncate table is not supported!" );
    }
    cmd = truncateStatement + ";";

    try {
      executeSql( cmd );
    } catch ( Exception e ) {
      throw new KettleException( "Error while truncating table " + table, e );
    }

    // try to update the metadata registry
    util.updateMetadata( meta, -1 );
    if ( log.isDetailed() ) {
      logDetailed( "Successfull: " + cmd );
    }

  }

  public void drop() throws KettleException {

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