What causes "Conditional statements are not supported" in apache/cassandra?

Remove the conditional clause (IF NOT EXISTS / IF ) from the statement used with CQLSSTableWriter

apache/cassandra · error · java.lang.IllegalArgumentException

Conditional statements are not supported

Error message

Conditional statements are not supported

What it means

CQLSSTableWriter is a bulk-loading API that translates an INSERT/UPDATE bind into direct SSTable writes; it bypasses the normal write path, so Lightweight Transaction (LWT) conditions (IF ... EXISTS etc.) cannot be honored. When preparing the user-supplied modification statement, if preparedModificationStatement.hasConditions() the Builder throws IllegalArgumentException to reject conditional statements up front.

Solutions

Remove the conditional clause (IF NOT EXISTS / IF <condition>) from the statement used with CQLSSTableWriter
Ensure uniqueness out-of-band: check for existing keys beforehand or deduplicate the input data before loading
Use the regular driver/LWT path instead of CQLSSTableWriter if conditional semantics are required

Example fix

// before
String cql = "INSERT INTO ks.t (k, v) VALUES (?, ?) IF NOT EXISTS";
// after
String cql = "INSERT INTO ks.t (k, v) VALUES (?, ?)";

Defensive patterns

Strategy: validation

Validate before calling

if (cql.toUpperCase().matches(".*\\bIF\\s+(NOT\\s+EXISTS|.*=).*"))
    throw new IllegalArgumentException("CQLSSTableWriter does not support conditional statements");

Try / catch

try { builder.build(); }
catch (IllegalArgumentException e) {
    if (e.getMessage().equals("Conditional statements are not supported"))
        // strip IF clause and rebuild
}

Prevention

Keep bulk-load CQL in separate templates without LWT clauses
Validate statements for IF conditions before handing them to the builder
Use regular driver sessions when conditional writes are required

When it happens

Trigger: Passing a statement containing conditions to CQLSSTableWriter.builder().withPreparedStatement / RawStatement-based builders — e.g. 'INSERT INTO t ... IF NOT EXISTS' or 'UPDATE t ... IF col = x' — then calling build().

Common situations: Reusing application CQL strings that use LWT for idempotency inside a bulk-load script; copying statements from a coordinator path into an offline SSTable writer.

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 apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/4b9aaf7413a9214a. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/io/sstable/CQLSSTableWriter.java:917

            if (partitioner != null)
                builder.partitioner(partitioner);

            return builder.build();
        }

        /**
         * Prepares modification statement for writing data to SSTable
         *
         * @return prepared modification statement and it's bound names
         */
        private ModificationStatement prepareModificationStatement()
        {
            ClientState state = ClientState.forInternalCalls();
            ModificationStatement preparedModificationStatement = modificationStatement.prepare(state);
            preparedModificationStatement.validate(state);

            if (preparedModificationStatement.hasConditions())
                throw new IllegalArgumentException("Conditional statements are not supported");
            if (preparedModificationStatement.isCounter())
                throw new IllegalArgumentException("Counter modification statements are not supported");
            if (preparedModificationStatement.getBindVariables().isEmpty())
                throw new IllegalArgumentException("Provided preparedModificationStatement statement has no bind variables");

            return preparedModificationStatement;
        }
    }
}

View on GitHub (pinned to 88fd0f6a0e)