apache/cassandra · error · ConfigurationException

Invalid value for segment_write_buffer_size. Value must be…

Error message

Invalid value for segment_write_buffer_size. Value must be a positive integer less than 32768MiB

What it means

StorageAttachedIndexOptions.validate() enforces that segment_write_buffer_size does not exceed MAXIMUM_SEGMENT_BUFFER_MB (32768 MiB) for storage-attached indexes, throwing ConfigurationException otherwise. It guards against allocating an unreasonably large SAI segment write buffer.

Solutions

Lower segment_write_buffer_size to at most 32768MiB
Express the value with explicit units, e.g. 512MiB, to avoid unit confusion
Leave the default if unsure

Example fix

# before
segment_write_buffer_size: 64GiB
# after
segment_write_buffer_size: 512MiB

Defensive patterns

Strategy: validation

Validate before calling

if (config.storage_attached_indexes != null
    && config.storage_attached_indexes.segment_write_buffer_size.toMebibytes() > 32768)
    throw new IllegalArgumentException("segment_write_buffer_size must be <= 32768MiB");

Type guard

static boolean isValidSegmentBuffer(DataStorage.LongBytesProp v) {
    return v != null && v.toMebibytes() <= 32768;
}

Try / catch

try { saiOptions.validate(); }
catch (ConfigurationException e) { log.error("Fix segment_write_buffer_size: {}", e.getMessage()); throw e; }

Prevention

Write sizes with explicit units (e.g. 512MiB) to avoid unit confusion
Keep buffer sizes within documented maximums
Validate configs with cassandra config tooling before rollout

When it happens

Trigger: Setting segment_write_buffer_size in cassandra.yaml (or via a Config object) to a value above 32768MiB, then triggering validation at startup or config load.

Common situations: Very large buffers configured hoping to speed up SAI builds; unit mistakes (GiB vs MiB) producing oversized values; copied configs from environments with different limits.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/c50d5021c86070c2. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/config/StorageAttachedIndexOptions.java:43

{
    public static final int DEFAULT_SEGMENT_BUFFER_MB = 1024;

    @VisibleForTesting
    public static final int MAXIMUM_SEGMENT_BUFFER_MB = 32768;

    @VisibleForTesting
    public static final String INVALID_BUFFER_SIZE_ERROR = "Invalid value for segment_write_buffer_size. " +
                                                           "Value must be a positive integer less than " + MAXIMUM_SEGMENT_BUFFER_MB + "MiB";

    public DataStorageSpec.IntMebibytesBound segment_write_buffer_size = new DataStorageSpec.IntMebibytesBound(DEFAULT_SEGMENT_BUFFER_MB);
    
    public volatile boolean prioritize_over_legacy_index = false;

    public void validate()
    {
        if (segment_write_buffer_size.toMebibytes() > MAXIMUM_SEGMENT_BUFFER_MB)
        {
            throw new ConfigurationException(INVALID_BUFFER_SIZE_ERROR);
        }
    }
}

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