apache/cassandra · error · ConfigurationException

concurrent_materialized_view_builders should be strictly…

Error message

concurrent_materialized_view_builders should be strictly greater than 0, but was ${conf.concurrent_materialized_view_builders}

What it means

concurrent_materialized_view_builders sets how many materialized view build tasks may run concurrently; applySimpleConfig requires it to be strictly positive at startup and throws ConfigurationException otherwise.

Solutions

Set concurrent_materialized_view_builders to a positive integer (default 1) in cassandra.yaml
Remove the key to accept the default
To pause view building use nodetool viewbuildstatus / disable materialized views rather than an invalid 0
Restart the node

Example fix

// before (cassandra.yaml)
concurrent_materialized_view_builders: 0
// after
concurrent_materialized_view_builders: 1

Defensive patterns

Strategy: validation

Validate before calling

if (conf.concurrentMaterializedViewBuilders != null && conf.concurrentMaterializedViewBuilders <= 0)
    throw new IllegalArgumentException("concurrent_materialized_view_builders must be > 0");

Try / catch

try { DatabaseDescriptor.daemonInitialization(); }
catch (ConfigurationException e) { LOG.fatal(e.getMessage()); System.exit(1); }

Prevention

Keep the default (1) unless deliberately tuned
Use proper mechanisms (dropping views) instead of 0 to stop view building
Lint templated cassandra.yaml output for empty/zero numerics

When it happens

Trigger: Node startup with concurrent_materialized_view_builders: 0 or a negative value in cassandra.yaml.

Common situations: Operator attempting to stop view building by zeroing the setting; template default rendering 0; accidental comment splitting the value from a digit.

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/9543c2ff02695dc5. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/config/DatabaseDescriptor.java:973

        if (conf.memtable_cleanup_threshold < 0.01f)
            throw new ConfigurationException("memtable_cleanup_threshold must be >= 0.01, but was " + conf.memtable_cleanup_threshold, false);
        if (conf.memtable_cleanup_threshold > 0.99f)
            throw new ConfigurationException("memtable_cleanup_threshold must be <= 0.99, but was " + conf.memtable_cleanup_threshold, false);
        if (conf.memtable_cleanup_threshold < 0.1f)
            logger.warn("memtable_cleanup_threshold is set very low [{}], which may cause performance degradation", conf.memtable_cleanup_threshold);

        if (conf.concurrent_compactors == null)
            conf.concurrent_compactors = Math.min(8, Math.max(2, Math.min(FBUtilities.getAvailableProcessors(), conf.data_file_directories.length)));

        if (conf.concurrent_compactors <= 0)
            throw new ConfigurationException("concurrent_compactors should be strictly greater than 0, but was " + conf.concurrent_compactors, false);

        applyConcurrentValidations(conf);
        applyRepairCommandPoolSize(conf);
        applyThresholdsValidations(conf);

        if (conf.concurrent_materialized_view_builders <= 0)
            throw new ConfigurationException("concurrent_materialized_view_builders should be strictly greater than 0, but was " + conf.concurrent_materialized_view_builders, false);

        if (conf.num_tokens != null && conf.num_tokens > MAX_NUM_TOKENS)
            throw new ConfigurationException(String.format("A maximum number of %d tokens per node is supported", MAX_NUM_TOKENS), false);

        try
        {
            // if prepared_statements_cache_size option was set to "auto" then size of the cache should be "max(1/256 of Heap (in MiB), 10MiB)"
            preparedStatementsCacheSizeInMiB = (conf.prepared_statements_cache_size == null)
                                               ? Math.max(10, (int) (Runtime.getRuntime().maxMemory() / 1024 / 1024 / 256))
                                               : conf.prepared_statements_cache_size.toMebibytes();

            if (preparedStatementsCacheSizeInMiB == 0)
                throw new NumberFormatException(); // to escape duplicating error message

            // we need this assignment for the Settings virtual table - CASSANDRA-17734
            conf.prepared_statements_cache_size = new DataStorageSpec.LongMebibytesBound(preparedStatementsCacheSizeInMiB);
        }
        catch (NumberFormatException e)

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