prestodb/presto · error · QueryPreprocessorException

Query preprocessor exited

Error message

Query preprocessor exited 

What it means

QueryPreprocessorException thrown when the external preprocessor process terminates with a non-zero exit code. The CLI waits for the process, reads its stderr (with a 100ms timeout), and appends any captured stderr to the message to explain why the process failed.

Source

Thrown at presto-cli/src/main/java/com/facebook/presto/cli/QueryPreprocessor.java:174

                }
            }
            catch (QueryPreprocessorException e) {
                throw e;
            }
            catch (InterruptedException e) {
                Thread.currentThread().interrupt();
                throw new QueryPreprocessorException("Interrupted while preprocessing query");
            }
            catch (Throwable e) {
                throw new QueryPreprocessorException("Error preprocessing query: " + e.getMessage(), e);
            }

            // check we got a valid exit code
            if (exitCode != 0) {
                Optional<String> errorMessage = tryGetFutureValue(readStderr, 100, MILLISECONDS)
                        .flatMap(value -> Optional.ofNullable(emptyToNull(value.trim())));

                throw new QueryPreprocessorException("Query preprocessor exited " + exitCode +
                        errorMessage.map(message1 -> "\n===\n" + message1 + "\n===").orElse(""));
            }
            return result;
        });

        try {
            return task.get(timeout.toMillis(), MILLISECONDS);
        }
        catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            throw new QueryPreprocessorException("Interrupted while preprocessing query");
        }
        catch (ExecutionException e) {
            Throwable cause = e.getCause();
            propagateIfPossible(cause, QueryPreprocessorException.class);
            throw new QueryPreprocessorException("Error preprocessing query: " + cause.getMessage(), cause);
        }
        catch (TimeoutException e) {

View on GitHub (pinned to 55bb57d202)

Solutions

1. Read the stderr block (=== ... ===) appended to the message; it usually states the process failure.
2. Run the preprocessor command manually against the same SQL to see the error.
3. Fix the script's bugs/missing dependencies and ensure it exits 0 on success.
4. Check the shebang line and PATH inside the environment the CLI runs in.
5. If the preprocessor intentionally rejects queries, adjust its exit/protocol handling to match the expected contract.

Example fix

// before (script exits non-zero on heredoc quoting bug)
#!/usr/bin/env python3
main(sys.argv[1:])
// after
#!/usr/bin/env python3
if __name__ == "__main__":
    sys.exit(main(sys.argv[1:]) or 0)

// dry-run the preprocessor and check its exit code
your-preprocessor.sh < sample.sql >/dev/null; echo $?  # must be 0

try {
    preprocessQuery(query);
} catch (QueryPreprocessorException e) {
    if (e.getMessage().startsWith("Query preprocessor exited")) {
        log.error("preprocessor process failed; stderr captured in message: {}", e.getMessage());
    }
    throw e;
}

When it happens

Trigger: The command given via --preprocessor-command exits with a status != 0; any crash, shell error, or explicit exit failure in the preprocessor script while preprocessing a query.

Common situations: Preprocessor script references a missing interpreter (bad shebang); script hits an error on specific SQL syntax; missing dependencies in the preprocessor environment; preprocessor rejects the query text by design.

Related errors

• Error preprocessing query:
• Timed out waiting for query preprocessor after
• both --execute and --file specified
• Error reading from file %s: %s
• No console from which to read password

AI-assisted analysis of prestodb/presto@55bb57d202 (2026-09-04). Data as JSON: /api/errors/5bb3d72990569487. Report an issue: GitHub.