apache/cassandra · error · InvalidRequestException

Write operation require a read but consistency %s is not sup

Error message

Write operation require a read but consistency %s is not supported on reads

What it means

ModificationStatement.readRequiredLists() is used when a write (e.g. UPDATE with a list add/remove) must first read existing data. Before issuing those reads it validates the statement's consistency level via cl.validateForRead(); if the level is invalid for reads (e.g. SOME variants of serial write levels), this InvalidRequestException is thrown naming the offending level.

Source

Thrown at src/java/org/apache/cassandra/cql3/statements/ModificationStatement.java:652

    private <F> Map<DecoratedKey, Partition> readRequiredLists(Collection<ByteBuffer> partitionKeys,
                                                           java.util.function.Function<F, ClusteringIndexFilter> filterBuilder,
                                                           F filterArg,
                                                           DataLimits limits,
                                                           boolean local,
                                                           ConsistencyLevel cl,
                                                           long nowInSeconds,
                                                           Dispatcher.RequestTime requestTime)
    {
        if (!requiresRead())
            return null;

        try
        {
            cl.validateForRead();
        }
        catch (InvalidRequestException e)
        {
            throw new InvalidRequestException(String.format("Write operation require a read but consistency %s is not supported on reads", cl));
        }

        List<SinglePartitionReadCommand> commands = new ArrayList<>(partitionKeys.size());
        for (ByteBuffer key : partitionKeys)
            commands.add(SinglePartitionReadCommand.create(metadata(),
                                                           nowInSeconds,
                                                           ColumnFilter.selection(this.requiresRead),
                                                           RowFilter.none(),
                                                           limits,
                                                           metadata().partitioner.decorateKey(key),
                                                           filterBuilder.apply(filterArg)));

        SinglePartitionReadCommand.Group group = SinglePartitionReadCommand.Group.create(commands, DataLimits.NONE);

        if (local)
        {
            try (ReadExecutionController executionController = group.executionController();
                 PartitionIterator iter = group.executeInternal(executionController))

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Check the consistency level being sent with the list-modifying statement and switch to a level valid for reads (e.g. ONE/QUORUM).
2. Verify client-side CL configuration; set per-statement CL instead of a global invalid one.
3. Ensure the driver/tool is not sending serial-only levels as regular consistency.

Example fix

// before
stmt.setConsistencyLevel(ConsistencyLevel.LOCAL_SERIAL); // invalid for the read phase
// after
stmt.setConsistencyLevel(ConsistencyLevel.QUORUM);

if (stmtTouchingLists && !isReadValidConsistency(cl)) { cl = ConsistencyLevel.QUORUM; }

try { session.execute(stmt); } catch (InvalidRequestException e) { if (e.getMessage().contains("not supported on reads")) { /* fix CL and retry */ } else throw e; }

When it happens

Trigger: Executing an UPDATE or DELETE that touches list columns (read-before-write) with a consistency level that fails validateForRead(), e.g. passing an inappropriate CL to the driver for such a statement.

Common situations: Application configures a custom consistency level globally, then runs list mutations; scripts generated for normal writes reused for list writes.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• Invalid empty consistency level
• Invalid null value of timestamp
• A TTL must be greater or equal to 0, but was <ttl>
• ttl is too large. requested (%d) maximum (%d)
• Counter and non-counter mutations cannot exist in the same b

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/ab6e1847bb78c790. Report an issue: GitHub.