1. Diagnostic Check:

   
# Check current file descriptor limits
ulimit -n
cat /proc/sys/fs/file-max

2. Temporary Immediate Fix:

   
# Increase file descriptor limit for current session
sudo ulimit -n 102400

3. Permanent System Configuration:

   Edit `/etc/security/limits.conf`:
   sudo nano /etc/security/limits.conf
   Then, add the following lines:

   
* soft nofile 102400
* hard nofile 102400

4. Systemd Service Configuration:

   Edit MongoDB service file:

   sudo nano /etc/systemd/system/mongodb.service

   Then, add the following under `[Service]`:

   
LimitNOFILE=infinity
LimitNPROC=infinity


   After that, reload and restart MongoDB:

   
sudo systemctl daemon-reload
sudo systemctl restart mongodb


1. Optimize queries by breaking large pipelines into smaller stages.
2. Use indexing to speed up query execution.
3. Reduce query complexity and scope.

Here are some optimization techniques:

• Query Redesign
  1. Use `$match` early in the pipeline to minimize dataset size.
  2. Implement pagination to reduce the dataset per query.
• Indexing Strategy

  
// Create compound indexes
db.collection.createIndex({ field1: 1, field2: -1 })

• Query Performance Monitoring
  1. Use `explain()` to analyze query execution plans.
  2. Set query timeouts to prevent resource exhaustion.

1. Implement proper connection pooling.
2. Explicitly close database connections after use.

   
# Connection Pooling Example (Python)
```python
from pymongo import MongoClient
client = MongoClient(
host='localhost',
port=27017,
maxPoolSize=100, # Maximum connection pool size
minPoolSize=10, # Minimum maintained connections
maxIdleTimeMS=30000 # Connection idle timeout
)


   Best Practices:

   1. Always close database connections explicitly.
   2. Use connection retry mechanisms.
   3. Configure appropriate timeouts.

1. Increase `net.maxIncomingConnections` in MongoDB.
2. Properly configure WiredTiger’s cache size.

We can adjust MongoDB Configuration by editing `mongod.conf`:


storage:
wiredTiger:
engineConfig:
cacheSizeGB: 4
statisticsLogDelaySecs: 0
net:
maxIncomingConnections: 65536


We can finetune performance with these steps:

• Monitor cache hit rates.
• Use SSD storage for better I/O performance.

• Use sequential backups to minimize open file count.
• Configure backup agents with proper file limits.

Here is a backup strategy:

• Sequential backup approach:

  mongodump --db=myDatabase --out=/backup/path –numParallelCollections=4
• Backup Optimization
  • Implement incremental backups.
  • Use compression to reduce storage space.
  • Schedule backups during low-traffic periods.

• Increase file descriptor limits for replica set nodes.
• Optimize initial sync configurations.

• Replica Set Configuration

  Edit `mongodb.conf`:

  replication:
oplogSizeMB: 10240
syncPeriodSecs: 60

• Performance Monitoring
  • Use MongoDB monitoring tools to track replication lag.
  • Implement error handling for failed synchronizations.

• Upgrade hardware to meet database demands.
• Optimize system-level configurations.

Recommended Hardware:

• Enterprise-grade SSDs for fast I/O.
• Minimum 16GB RAM for large workloads.
• Multi-core CPU for parallel query execution.

System Configuration Optimization:


# Increase max open files
sudo sysctl -w fs.file-max=2097152
# Reduce swap usage for better performance
sudo sysctl -w vm.swappiness=10