apache/cassandra · error · ConfigurationException

compressed_read_ahead_buffer_size must be at least 256KiB (s

Error message

compressed_read_ahead_buffer_size must be at least 256KiB (set to 0 to disable), but was <value>

What it means

When compression read-ahead is enabled, the buffer used to read ahead of the compression offset must be either disabled (0) or at least 256 KiB, matching the compression chunk minimum. DatabaseDescriptor throws this ConfigurationException with the actual value when the size is strictly between 0 and 256 KiB.

Source

Thrown at src/java/org/apache/cassandra/config/DatabaseDescriptor.java:1189

        if (conf.max_value_size.toMebibytes() == 0)
            throw new ConfigurationException("max_value_size must be positive", false);
        else if (conf.max_value_size.toMebibytes() >= 2048)
            throw new ConfigurationException("max_value_size must be smaller than 2048, but was "
                                             + conf.max_value_size.toString(), false);

        switch (conf.disk_optimization_strategy)
        {
            case ssd:
                diskOptimizationStrategy = new SsdDiskOptimizationStrategy(conf.disk_optimization_page_cross_chance);
                break;
            case spinning:
                diskOptimizationStrategy = new SpinningDiskOptimizationStrategy();
                break;
        }

        if (conf.compressed_read_ahead_buffer_size.toKibibytes() > 0 && conf.compressed_read_ahead_buffer_size.toKibibytes() < 256)
            throw new ConfigurationException("compressed_read_ahead_buffer_size must be at least 256KiB (set to 0 to disable), but was " + conf.compressed_read_ahead_buffer_size, false);

        if (conf.server_encryption_options != null)
        {
            conf.server_encryption_options.applyConfig();

            if (conf.server_encryption_options.legacy_ssl_storage_port_enabled &&
                conf.server_encryption_options.tlsEncryptionPolicy() == EncryptionOptions.TlsEncryptionPolicy.UNENCRYPTED)
            {
                throw new ConfigurationException("legacy_ssl_storage_port_enabled is true (enabled) with internode encryption disabled (none). Enable encryption or disable the legacy ssl storage port.");
            }
        }

        if (conf.internode_max_message_size != null)
        {
            long maxMessageSize = conf.internode_max_message_size.toBytes();

            if (maxMessageSize > conf.internode_application_receive_queue_reserve_endpoint_capacity.toBytes())
                throw new ConfigurationException("internode_max_message_size must no exceed internode_application_receive_queue_reserve_endpoint_capacity", false);

View on GitHub (pinned to 88fd0f6a0e)

Solutions

Set compressed_read_ahead_buffer_size_in_kb to 256 or larger
Set it to 0 to explicitly disable compressed read-ahead
Remove the override to use the default (64 MiB)

Example fix

# before (cassandra.yaml)
compressed_read_ahead_buffer_size_in_kb: 100
# after
compressed_read_ahead_buffer_size_in_kb: 0

Defensive patterns

Strategy: validation

Validate before calling

long kib = conf.compressed_read_ahead_buffer_size.toKibibytes();
if (kib > 0 && kib < 256) throw new IllegalArgumentException("compressed_read_ahead_buffer_size must be 0 or >= 256 KiB");

Try / catch

try { DatabaseDescriptor.applyConfig(conf); } catch (ConfigurationException e) { if (e.getMessage().contains("compressed_read_ahead_buffer_size")) { /* set to 0 or >= 256KiB */ } }

Prevention

Only tune read-ahead in multiples of the 256 KiB compression chunk floor
Use 0 to disable rather than a small positive buffer
Confirm units (KiB) when copying tuning values

When it happens

Trigger: cassandra.yaml sets compressed_read_ahead_buffer_size_in_kb to a positive value below 256 (e.g. 64) and DatabaseDescriptor.applySimpleConfig runs at startup.

Common situations: Misunderstanding the unit (setting 100 meaning 100 KiB but expecting bytes-scale tolerance); tuning down memory usage below the minimum; stale configs from older versions with different minimums.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/3d2eed9b80c8169d. Report an issue: GitHub.