pentaho/pentaho-kettle · error · KettleException

An error occurred writing data to the MonetDB API (MAPI)…

Error message

An error occurred writing data to the MonetDB API (MAPI) process

What it means

Catch-all wrapper for the entire writeBufferToMonetDB() body: any exception thrown while streaming buffered rows to the MAPI mserver process (I/O errors on the socket streams, process died, or the nested KettleExceptions above) is rethrown as this KettleException with the original as cause. It means the pipe to the MonetDB bulk-loader process broke during a write.

Solutions

1. Inspect the wrapped cause (e.g. IOException/broken pipe) to see if the mserver process died
2. Check MonetDB server logs around the failure time for crashes or fatal errors
3. Verify the connection stays alive (timeouts, firewall idle disconnects) during long loads
4. Re-run the transformation; if a bad row killed the session, fix the data or enable compatibility mode

// before writing, confirm the mserver process/socket is alive
if ( !data.mserverAlive() ) reopenConnection();

if ( data == null || data.out == null || data.in == null ) throw new KettleException( "MAPI streams not initialized" );

try { writeBuffer(); } catch ( KettleException e ) { if ( e.getCause() instanceof IOException ) { reconnect and retry the batch once; } else rethrow; }

When it happens

Trigger: data.out.writeLine() fails because the mserver subprocess has exited (server crash, killed process, socket closed); waitForPrompt() throws; or any other Exception during buffer flushing is caught by the outer catch block.

Common situations: MonetDB server restarted or crashed mid-load; mserver terminated due to a previous fatal COPY error closing stdin; network/pipe interruption; misconfigured MAPI connection dropped during the transaction.

Related errors

• Error loading data:
• Error serializing rows of data to the fifo file
• Error while closing output
• Error while creating table
• Error while dropping table

AI-assisted analysis of pentaho/pentaho-kettle@f3058517a1 (2026-09-13). Data as JSON: /api/errors/aa2be5f6bc4d8e04. 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:521

        // write an empty line, forces the flush of the stream
        data.out.writeLine( "" );

        // again...
        error = data.in.waitForPrompt();
        if ( error != null ) {
          throw new KettleException( "Error loading data: " + error );
        }
      }

      if ( log.isRowLevel() ) {
        logRowlevel( Const.CR );
      }

      // reset the buffer pointer...
      //
      data.bufferIndex = 0;
    } catch ( Exception e ) {
      throw new KettleException( "An error occurred writing data to the MonetDB API (MAPI) process", e );
    }
  }

  protected void verifyDatabaseConnection() throws KettleException {
    // Confirming Database Connection is defined.
    if ( meta.getDatabaseMeta() == null ) {
      throw new KettleException( BaseMessages.getString( PKG, "MonetDBBulkLoaderMeta.GetSQL.NoConnectionDefined" ) );
    }
  }

  @Override
  public boolean init( StepMetaInterface smi, StepDataInterface sdi ) {
    meta = (MonetDBBulkLoaderMeta) smi;
    data = (MonetDBBulkLoaderData) sdi;

    if ( super.init( smi, sdi ) ) {

      try {

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