Cassandra Driver Best Practices

This page consolidates production configuration recommendations for Cassandra drivers.

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Session Management

Single Session per Application

Create one session and reuse it throughout the application lifecycle:

// CORRECT: Single session, created once
public class CassandraConfig {
    private static CqlSession session;

    public static synchronized CqlSession getSession() {
        if (session == null) {
            session = CqlSession.builder()
                .withLocalDatacenter("dc1")
                .build();
        }
        return session;
    }

    public static void shutdown() {
        if (session != null) {
            session.close();
        }
    }
}

// WRONG: Session per request
public User getUser(UUID id) {
    try (CqlSession session = CqlSession.builder().build()) {  // Expensive!
        return session.execute(...);
    }
}

Aspect	Single Session	Session per Request
Connection overhead	Once at startup	Every request
Metadata discovery	Once	Every request
Prepared statement cache	Shared	Rebuilt each time
Resource usage	Predictable	Unbounded

Graceful Shutdown

Close the session cleanly on application shutdown:

Runtime.getRuntime().addShutdownHook(new Thread(() -> {
    session.close();  // Waits for in-flight requests
}));

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Connection Configuration

Contact Points

Provide multiple contact points for initial connection:

CqlSession session = CqlSession.builder()
    .addContactPoint(new InetSocketAddress("10.0.1.1", 9042))
    .addContactPoint(new InetSocketAddress("10.0.1.2", 9042))
    .addContactPoint(new InetSocketAddress("10.0.1.3", 9042))
    .withLocalDatacenter("dc1")
    .build();

The driver only needs one successful connection to discover the full cluster topology, but multiple contact points provide redundancy during startup.

Local Datacenter

In Java driver 4.x, local datacenter configuration is mandatory regardless of cluster topology. Session creation fails with IllegalStateException if omitted:

// REQUIRED (driver 4.x, any topology)
.withLocalDatacenter("dc1")

In multi-DC deployments, this setting also ensures the driver routes queries to the correct datacenter.

Connection Pool Sizing

Default pool settings work for most workloads. Adjust only when:

• Measured stream exhaustion occurs
• Throughput exceeds tens of thousands requests/second per node
• Monitoring shows pool-related bottlenecks

In driver 4.x, pool sizing is configured via application.conf:

datastax-java-driver {
  advanced.connection.pool {
    local.size = 2   // connections per local node (default: 1)
    remote.size = 1  // connections per remote node (default: 1)
  }
}

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Query Execution

Use Prepared Statements

Prepare all production queries:

// Prepare once at startup
private final PreparedStatement selectUser = session.prepare(
    "SELECT * FROM users WHERE user_id = ?");

// Execute with bound values
public User getUser(UUID userId) {
    Row row = session.execute(selectUser.bind(userId)).one();
    return mapToUser(row);
}

Benefits:

• Reduced parsing overhead
• Enables token-aware routing (via routing key metadata bound to the statement)
• Protection against CQL injection

Set Appropriate Consistency Levels

Choose consistency level based on requirements:

Statement statement = selectUser.bind(userId)
    .setConsistencyLevel(ConsistencyLevel.LOCAL_QUORUM);  // Explicit

Use Case	Recommended CL
Strong consistency reads	LOCAL_QUORUM
Strong consistency writes	LOCAL_QUORUM
Eventually consistent reads	LOCAL_ONE
Analytics/reporting	ONE
Cross-DC consistency	QUORUM or EACH_QUORUM

Set Query Timeouts

Configure appropriate timeouts:

Statement statement = selectUser.bind(userId)
    .setTimeout(Duration.ofSeconds(5));  // Query-specific timeout

Timeout Type	Typical Range	Notes
Read timeout	5-10 seconds	Should exceed expected P99; align with server-side read_request_timeout
Write timeout	10-30 seconds	Should align with server-side write_request_timeout; varies by workload
Connection timeout	5 seconds	Adjust for network conditions

Client-side timeouts should be set relative to server-side timeouts and application SLA requirements.

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Error Handling

Handle Specific Exceptions

try {
    session.execute(statement);
} catch (NoNodeAvailableException e) {
    // All nodes down - circuit breaker or fail
    log.error("Cluster unavailable", e);
    throw new ServiceUnavailableException();

} catch (QueryExecutionException e) {
    if (e instanceof ReadTimeoutException) {
        // Replica(s) didn't respond - may retry
        ReadTimeoutException rte = (ReadTimeoutException) e;
        log.warn("Read timeout: received {}/{} required",
            rte.getReceived(), rte.getRequired());

    } else if (e instanceof WriteTimeoutException) {
        // Write may or may not have succeeded
        WriteTimeoutException wte = (WriteTimeoutException) e;
        log.error("Write timeout for {}: received {}/{}",
            wte.getWriteType(), wte.getReceived(), wte.getRequired());
        // DO NOT retry non-idempotent writes automatically

    } else if (e instanceof UnavailableException) {
        // Not enough replicas alive
        UnavailableException ue = (UnavailableException) e;
        log.warn("Unavailable: alive {}/{} required",
            ue.getAlive(), ue.getRequired());
    }
}

Idempotency Marking

Mark idempotent operations explicitly:

// Safe to retry
Statement readStatement = selectUser.bind(userId)
    .setIdempotent(true);

// NOT safe to retry
Statement counterStatement = updateCounter.bind(pageId)
    .setIdempotent(false);

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Policy Configuration

Production Policy Template

CqlSession session = CqlSession.builder()
    .addContactPoints(contactPoints)
    .withLocalDatacenter("dc1")

    // Load balancing: configured via application.conf
    // basic.load-balancing-policy.local-datacenter = "dc1"

    // Retry: conservative, respects idempotency
    .withRetryPolicy(DefaultRetryPolicy.INSTANCE)

    // Reconnection: exponential backoff
    .withReconnectionPolicy(
        ExponentialReconnectionPolicy.builder()
            .withBaseDelay(Duration.ofSeconds(1))
            .withMaxDelay(Duration.ofMinutes(5))
            .build())

    // Speculative execution: disabled by default
    // Enable only for idempotent, latency-sensitive queries
    // .withSpeculativeExecutionPolicy(...)

    .build();

Per-Query Policy Override

Override policies for specific query types:

// Latency-sensitive read with speculative execution
Statement fastRead = selectUser.bind(userId)
    .setIdempotent(true)
    .setSpeculativeExecutionPolicy(speculativePolicy);

// Non-idempotent write with no retry
Statement counterUpdate = incrementCounter.bind(pageId)
    .setIdempotent(false)
    .setRetryPolicy(FallthroughRetryPolicy.INSTANCE);

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Monitoring

Essential Metrics

Monitor these driver metrics:

Metric Category	Key Metrics
Latency	Request latency percentiles (P50, P95, P99)
Throughput	Requests per second
Errors	Error rate by type (timeout, unavailable, etc.)
Connections	Open connections per node
Pool	In-flight requests, available streams
Retries	Retry rate, retry success rate
Speculative	Trigger rate, win rate

Health Checks

Implement application health checks:

public boolean isHealthy() {
    try {
        // Simple query to verify connectivity
        session.execute("SELECT now() FROM system.local");
        return true;
    } catch (Exception e) {
        return false;
    }
}

Logging

Configure appropriate driver logging:

<!-- Log connection events -->
<logger name="com.datastax.oss.driver.internal.core.pool" level="INFO"/>

<!-- Log retries and speculative execution -->
<logger name="com.datastax.oss.driver.internal.core.retry" level="DEBUG"/>

<!-- Reduce noise from metadata refresh -->
<logger name="com.datastax.oss.driver.internal.core.metadata" level="WARN"/>

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Common Anti-Patterns

Anti-Pattern	Problem	Solution
Session per request	Massive overhead	Single shared session
Unprepared statements in loops	Parsing overhead, no token-aware	Prepare and reuse
Ignoring local datacenter	Cross-DC latency	Configure explicitly
Retrying non-idempotent writes	Data corruption	Mark idempotency, custom retry
Unbounded IN clauses	Prepared statement cache churn	Fixed sizes or pagination
Synchronous calls in async context	Thread pool exhaustion	Use async API consistently
No timeout configuration	Requests hang indefinitely	Set explicit timeouts
Catching generic Exception	Hides specific error handling	Catch specific exceptions

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Checklist

Before deploying to production:

• Single session instance shared across application
• Local datacenter configured explicitly
• All queries use prepared statements
• Consistency levels set explicitly
• Timeouts configured appropriately
• Idempotent operations marked
• Error handling for specific exception types
• Driver metrics exported to monitoring
• Health check endpoint implemented
• Graceful shutdown configured
• Connection pool sized appropriately (if non-default)
• Retry policy reviewed for workload
• Speculative execution evaluated (if latency-sensitive)

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Related Documentation

• Connection Management — Connection pooling details
• Policies — Policy configuration reference
• Prepared Statements — Statement preparation and caching