apache/cassandra · critical · IllegalArgumentException

Unknown commitlog service type: <commitLogSync>

Error message

Unknown commitlog service type: <commitLogSync>

What it means

CommitLog's constructor creates a CommitLogExecutorService based on the configured commitlog_sync mode (periodic, batch, group). If DatabaseDescriptor.getCommitLogSync() returns a value with no matching case, it throws IllegalArgumentException "Unknown commitlog service type". This guards against unhandled enum values, e.g. from a newer config parsed by an older binary.

Source

Thrown at src/java/org/apache/cassandra/db/commitlog/CommitLog.java:129

                                               DatabaseDescriptor.getCommitLogWriteDiskAccessMode());
        DatabaseDescriptor.createAllDirectories();

        this.archiver = archiver;
        metrics = new CommitLogMetrics();

        switch (DatabaseDescriptor.getCommitLogSync())
        {
            case periodic:
                executor = new PeriodicCommitLogService(this);
                break;
            case batch:
                executor = new BatchCommitLogService(this);
                break;
            case group:
                executor = new GroupCommitLogService(this);
                break;
            default:
                throw new IllegalArgumentException("Unknown commitlog service type: " + DatabaseDescriptor.getCommitLogSync());
        }

        segmentManager = segmentManagerProvider.apply(this);

        // register metrics
        metrics.attach(executor, segmentManager);
    }

    /**
     * Tries to start the CommitLog if not already started.
     */
    synchronized public CommitLog start()
    {
        if (started)
            return this;

        try
        {

View on GitHub (pinned to 88fd0f6a0e)

Solutions

1. Set commitlog_sync in cassandra.yaml to one of: periodic, batch, or group (matching your Cassandra version's supported values)
2. Check the exact spelling/case of the value; compare against Config.CommitLogSync in your binary's version
3. Remove config values inherited from a newer Cassandra version if you downgraded, or upgrade the binary instead
4. Validate config with the target version's documentation before deployment

Example fix

// before (cassandra.yaml)
commitlog_sync: twync
// after
commitlog_sync: periodic

Set<String> valid = Set.of("periodic", "batch", "group");
String mode = yaml.get("commitlog_sync");
if (!valid.contains(mode)) throw new IllegalArgumentException("Unsupported commitlog_sync: " + mode);

null

try { startCassandra(); } catch (IllegalArgumentException e) { if (e.getMessage().contains("Unknown commitlog service type")) { /* correct commitlog_sync value and restart */ } else throw e; }

When it happens

Trigger: Setting an invalid or unsupported commitlog_sync value in cassandra.yaml, or a config from a newer Cassandra version whose new sync mode is not understood by the running binary.

Common situations: Typo like commitlog_sync: Periodic (case-sensitive enum parse) or an unknown mode name; rolling back a version downgrade where the new mode persisted in config is unsupported; hand-edited yaml with an invented value.

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

• commitlog_directory must be specified
• Commit log flush interval must be positive: %fms
• Unable to parse precision of value
• %s has authorization enabled which requires %s to enable aut
• %s requires %s

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/2b5344208c3f2312. Report an issue: GitHub.