What causes "Error creating/updating event handler: %s/%s" in conductor-oss/conductor?

Verify Cassandra is reachable and the session is healthy.

conductor-oss/conductor · error · TransientException

Error creating/updating event handler: %s/%s

Error message

Error creating/updating event handler: %s/%s

What it means

Thrown by CassandraEventHandlerDAO.insertOrUpdateEventHandler when inserting/updating an event handler row fails. DriverException during session.execute(insertEventHandlerStatement.bind(...)) is wrapped in TransientException. Triggered by addEventHandler and updateEventHandler paths.

Source

Thrown at cassandra-persistence/src/main/java/com/netflix/conductor/cassandra/dao/CassandraEventHandlerDAO.java:145

            LOGGER.error(errorMsg, e);
            throw new TransientException(errorMsg, e);
        }
    }

    private void insertOrUpdateEventHandler(EventHandler eventHandler) {
        try {
            String handler = toJson(eventHandler);
            session.execute(insertEventHandlerStatement.bind(eventHandler.getName(), handler));
            recordCassandraDaoRequests("storeEventHandler");
            recordCassandraDaoPayloadSize("storeEventHandler", handler.length(), "n/a", "n/a");
        } catch (DriverException e) {
            Monitors.error(CLASS_NAME, "insertOrUpdateEventHandler");
            String errorMsg =
                    String.format(
                            "Error creating/updating event handler: %s/%s",
                            eventHandler.getName(), eventHandler.getEvent());
            LOGGER.error(errorMsg, e);
            throw new TransientException(errorMsg, e);
        }
    }
}

View on GitHub (pinned to cf7c3e4a8a)

Solutions

Verify Cassandra is reachable and the session is healthy.
Confirm the event_handler table and its columns match the prepared statement (re-run init if schema drifted).
Retry the write — TransientException is retryable.
If the handler JSON is large, check it is within Cassandra's text column / row size limits.

Defensive patterns

Strategy: validation

Validate before calling

// Validate the handler before persisting
if (eventHandler == null || isBlank(eventHandler.getName()) || isBlank(eventHandler.getEvent())) {
    throw new IllegalArgumentException("event handler name and event required");
}

Try / catch

try {
    dao.addEventHandler(eventHandler);
} catch (TransientException e) {
    log.warn("Transient failure storing handler {}; retrying", eventHandler.getName());
    throw e;

Prevention

Validate handler name/event are non-blank before insert.
Retry TransientException with exponential backoff.
Keep handler payloads small to avoid column-size limits.

When it happens

Trigger: Calling addEventHandler/updateEventHandler with a handler whose JSON is too large for the column, when Cassandra is unavailable, or when the write times out / exceeds consistency.

Common situations: Cassandra connectivity loss. Write timeout under load. Schema mismatch (table/columns missing). A very large EventHandler payload exceeding column limits.

Related errors

AI-assisted analysis of conductor-oss/conductor@cf7c3e4a8a (2026-08-14). Data as JSON: /api/errors/a3e3bb940f1de2fd. Report an issue: GitHub.