How to fix StaleShardVersion: shard version mismatch in MongoDB

// Example in Node.js MongoDB driver
const client = new MongoClient(uri, {
  retryWrites: true,
  retryReads: true,
  maxPoolSize: 10,
  minPoolSize: 5,
});

// Or implement custom retry logic
async function executeWithRetry(operation, maxRetries = 3) {
  for (let i = 0; i < maxRetries; i++) {
    try {
      return await operation();
    } catch (error) {
      if (error.code === 63 || error.codeName === 'StaleShardVersion') {
        // Wait before retrying (exponential backoff)
        await new Promise(resolve =>
          setTimeout(resolve, Math.pow(2, i) * 100)
        );
        continue;
      }
      throw error;
    }
  }
  throw new Error('Max retries exceeded');
}

// Check balancer status
use config
db.locks.find({ _id: "balancer" })

// Check chunk distribution
db.getSiblingDB("config").chunks.find().count()

// Monitor active migrations
db.currentOp().inprog.forEach(op => {
  if (op.desc && op.desc.includes("migrate")) {
    printjson(op);
  }
})

# Check mongos logs
tail -f /var/log/mongodb/mongos.log | grep -i "balancer|migrate"

# Check config server logs
tail -f /var/log/mongodb/mongod-config.log

// For MongoDB Node.js driver, you can:
// 1. Reconnect the client
await client.close();
await client.connect();

// 2. Clear operation-specific caches (if available)
// Some drivers allow clearing session or metadata caches

// 3. Ensure you're using the latest driver version
// Older drivers may have bugs in metadata handling

// Check chunk size settings
use config
db.settings.findOne({ _id: "chunksize" })

// View chunk distribution per shard
db.getSiblingDB("config").chunks.aggregate([
  { $group: { _id: "$shard", count: { $sum: 1 } } }
])

// Check for jumbo chunks (too large to migrate)
db.getSiblingDB("config").chunks.find({ jumbo: true })

// Check network connectivity
// From each mongos to each shard and config server
const hosts = ['shard1:27017', 'shard2:27017', 'config1:27019'];
for (const host of hosts) {
  try {
    const testClient = new MongoClient(`mongodb://${host}/test`, {
      serverSelectionTimeoutMS: 5000,
      connectTimeoutMS: 10000,
      socketTimeoutMS: 30000
    });
    await testClient.connect();
    console.log(`✓ ${host} reachable`);
    await testClient.close();
  } catch (error) {
    console.error(`✗ ${host} unreachable:`, error.message);
  }
}

// Bad: Query without shard key (scatter-gather)
db.orders.find({ status: "pending" }) // If status is not shard key

// Good: Query with shard key prefix
db.orders.find({ customerId: "123", status: "pending" }) // If customerId is shard key

// Check query patterns
db.currentOp().inprog.forEach(op => {
  if (op.ns === "mydb.orders") {
    print(`Query: ${JSON.stringify(op.query)}`);
    print(`Shard key: ${op.shardKey}`);
  }
})