Unable to open hint directory using Native library…

Error message

Unable to open hint directory using Native library. Skipping sync.

What it means

HintsCatalog.fsyncDirectory tries to fsync the hints directory using the native library (JNA) to open a directory file descriptor. If the native library is enabled but the code runs in a client (dtest/tooling) context where DatabaseDescriptor client initialization is used, the native open is unavailable, so it logs this warning and skips the directory sync. Durability of the directory entry update is not guaranteed in that path.

Solutions

Ignore in test/client contexts — the sync skip is expected there
In production server startup, verify JNA is available (libjna on the classpath / nativelib extraction) so the real fsync path is used
Check that no 'cassandra.client' style initialization is accidentally used for a server process

Defensive patterns

Strategy: validation

Validate before calling

// caller-side: skip sync expectations in client mode
boolean canNativeSync = NativeLibrary.isEnabled() && !DatabaseDescriptor.isClientInitialized();

Prevention

In production, ensure JNA and native libs are available so directory fsync works
Treat the warning as expected in dtests/tools
Verify hints directory durability requirements for your deployment

When it happens

Trigger: fsyncDirectory called with NativeLibrary.isEnabled() true but DatabaseDescriptor.isClientInitialized() true — i.e. client mode (dtests, tools) where the server-side native directory open cannot be used.

Common situations: Running in-JVM distributed tests or offline tools that touch HintsCatalog; container images missing the JNA native bindings for server startup.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/20afe48b474c3fb3. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/hints/HintsCatalog.java:188

        {
            try
            {
                SyncUtil.trySync(fd);
                NativeLibrary.tryCloseFD(fd);
            }
            catch (FSError e) // trySync failed
            {
                logger.error("Unable to sync directory {}", hintsDirectory.absolutePath(), e);
                FileUtils.handleFSErrorAndPropagate(e);
            }
        }
        else if (!NativeLibrary.isEnabled())
        {
            return;
        }
        else if (DatabaseDescriptor.isClientInitialized())
        {
            logger.warn("Unable to open hint directory using Native library. Skipping sync.");
        }
        else
        {
            if (SyncUtil.SKIP_SYNC)
                return;
            logger.error("Unable to open directory {}", hintsDirectory.absolutePath());
            FileUtils.handleFSErrorAndPropagate(new FSWriteError(new IOException(String.format("Unable to open hint directory %s", hintsDirectory.absolutePath())), hintsDirectory.absolutePath()));
        }
    }

    ImmutableMap<String, Object> getWriterParams()
    {
        return writerParams;
    }
}

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